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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Nutr.</journal-id>
<journal-title>Frontiers in Nutrition</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Nutr.</abbrev-journal-title>
<issn pub-type="epub">2296-861X</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fnut.2023.1103330</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Nutrition</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Increased selenium and decreased iron levels in relation to risk of coronary artery disease in patients with diabetes</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author" equal-contrib="no">
<name>
<surname>Tian</surname>
<given-names>Mengyun</given-names>
</name>
<xref rid="aff1" ref-type="aff"><sup>1</sup></xref>
<xref rid="fn0001" ref-type="author-notes"><sup>&#x2020;</sup></xref>
<uri xlink:href="https://loop.frontiersin.org/people/2250035/overview"/>
</contrib>
<contrib contrib-type="author" equal-contrib="no">
<name>
<surname>Hu</surname>
<given-names>Teng</given-names>
</name>
<xref rid="aff1" ref-type="aff"><sup>1</sup></xref>
<xref rid="aff2" ref-type="aff"><sup>2</sup></xref>
<xref rid="fn0001" ref-type="author-notes"><sup>&#x2020;</sup></xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Ying</surname>
<given-names>Jiajun</given-names>
</name>
<xref rid="aff3" ref-type="aff"><sup>3</sup></xref>
<xref rid="aff4" ref-type="aff"><sup>4</sup></xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Cui</surname>
<given-names>Hanbin</given-names>
</name>
<xref rid="aff1" ref-type="aff"><sup>1</sup></xref>
<xref rid="aff2" ref-type="aff"><sup>2</sup></xref>
<xref rid="aff4" ref-type="aff"><sup>4</sup></xref>
<uri xlink:href="https://loop.frontiersin.org/people/1437129/overview"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Huangfu</surname>
<given-names>Ning</given-names>
</name>
<xref rid="aff1" ref-type="aff"><sup>1</sup></xref>
<xref rid="aff2" ref-type="aff"><sup>2</sup></xref>
<xref rid="aff4" ref-type="aff"><sup>4</sup></xref>
<xref rid="c001" ref-type="corresp"><sup>&#x002A;</sup></xref>
</contrib>
</contrib-group>
<aff id="aff1"><sup>1</sup><institution>Department of Cardiology, The First Affiliated Hospital of Ningbo University, School of Medicine, Ningbo University</institution>, <addr-line>Ningbo</addr-line>, <country>China</country></aff>
<aff id="aff2"><sup>2</sup><institution>Cardiovascular Disease Clinical Medical Research Center of Ningbo</institution>, <addr-line>Ningbo</addr-line>, <country>China</country></aff>
<aff id="aff3"><sup>3</sup><institution>Department of Cardiology, Ningbo First Hospital</institution>, <addr-line>Ningbo</addr-line>, <country>China</country></aff>
<aff id="aff4"><sup>4</sup><institution>Key Laboratory of Precision Medicine for Atherosclerotic Diseases of Zhejiang Province</institution>, <addr-line>Ningbo</addr-line>, <country>China</country></aff>
<author-notes>
<fn id="fn0002" fn-type="edited-by"><p>Edited by: Xiaohua Liang, Children&#x2018;s Hospital of Chongqing Medical University, China</p></fn>
<fn id="fn0003" fn-type="edited-by"><p>Reviewed by: Bojana B. Vidovic, University of Belgrade, Serbia; Jong Sung Kim, The University of Iowa, United States</p></fn>
<corresp id="c001">&#x002A;Correspondence: Ning Huangfu, <email>ninghuangfu@126.com</email></corresp>
<fn id="fn0001" fn-type="equal"><p><sup>&#x2020;</sup>These authors have contributed equally to this work</p></fn>
</author-notes>
<pub-date pub-type="epub">
<day>18</day>
<month>05</month>
<year>2023</year>
</pub-date>
<pub-date pub-type="collection">
<year>2023</year>
</pub-date>
<volume>10</volume>
<elocation-id>1103330</elocation-id>
<history>
<date date-type="received">
<day>29</day>
<month>11</month>
<year>2022</year>
</date>
<date date-type="accepted">
<day>03</day>
<month>05</month>
<year>2023</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#x00A9; 2023 Tian, Hu, Ying, Cui and Huangfu.</copyright-statement>
<copyright-year>2023</copyright-year>
<copyright-holder>Tian, Hu, Ying, Cui and Huangfu</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<sec>
<title>Background</title>
<p>Observational studies have reported inconsistent associations between micronutrient levels and the risk of coronary artery disease (CAD) in diabetic patients. We aim to explore the causal association between genetically predicted concentrations of micronutrients (phosphorus, magnesium, selenium, iron, zinc, and copper) and CAD in patients with diabetes.</p>
</sec>
<sec>
<title>Methods</title>
<p>Single nucleotide polymorphisms (SNPs) connected to serum micronutrient levels were extracted from the corresponding published genome-wide association studies (GWASs). Summary-level statistics for CAD in diabetic patients were obtained from a GWAS of 15,666 patients with diabetes. The primary analysis was carried out with the inverse variance weighted approach, and sensitivity analyses using other statistical methods were further employed to assess the robustness of the results.</p>
</sec>
<sec>
<title>Results</title>
<p>Genetically predicted selenium level was causally associated with a higher risk of CAD in diabetic patients (odds ratio [OR]: 1.25; 95% confidence interval [CI]: 1.10&#x2013;1.42; <italic>p</italic>&#x2009;=&#x2009;5.01&#x2009;&#x00D7;&#x2009;10<sup>&#x2212;4</sup>). While, genetically predicted iron concentrations in patients with diabetes were inversely associated with the risk of CAD (OR: 0.82; 95% CI: 0.75&#x2013;0.90; <italic>p</italic>&#x2009;=&#x2009;2.16&#x2009;&#x00D7;&#x2009;10<sup>&#x2212;5</sup>). The association pattern kept robust in most sensitivity analyses. Nominally significant associations were observed for magnesium and copper with the risk of CAD in patients with diabetes. No consistent evidence was found for the causal associations between phosphorus and zinc levels, and the risk of CAD in patients with diabetes.</p>
</sec>
<sec>
<title>Conclusion</title>
<p>We provide consistent evidence for the causal effect of increased selenium and decreased iron levels on CAD in patients with diabetes, highlighting the necessity of micronutrient monitoring and application in these patients.</p>
</sec>
</abstract>
<kwd-group>
<kwd>micronutrient</kwd>
<kwd>coronary artery disease</kwd>
<kwd>diabetes</kwd>
<kwd>causal association</kwd>
<kwd>selenium</kwd>
<kwd>iron</kwd>
</kwd-group>
<contract-num rid="cn1">2022E10026</contract-num>
<contract-num rid="cn2">82200489</contract-num>
<contract-num rid="cn3">2021Z134</contract-num>
<contract-num rid="cn4">2021C03096</contract-num>
<contract-num rid="cn5">202002N3175</contract-num>
<contract-sponsor id="cn1">Key Laboratory of Precision Medicine for Atherosclerotic Diseases of Zhejiang Province, China</contract-sponsor>
<contract-sponsor id="cn2">National Natural Science Foundation of China<named-content content-type="fundref-id">10.13039/501100001809</named-content></contract-sponsor>
<contract-sponsor id="cn3">Major Project of Science and Technology Innovation 2025 in Ningbo, China</contract-sponsor>
<contract-sponsor id="cn4">Zhejiang Province, China</contract-sponsor>
<contract-sponsor id="cn5">Public Science and Technology Projects of Ningbo</contract-sponsor>
<counts>
<fig-count count="2"/>
<table-count count="2"/>
<equation-count count="0"/>
<ref-count count="58"/>
<page-count count="8"/>
<word-count count="6123"/>
</counts>
<custom-meta-wrap>
<custom-meta>
<meta-name>section-at-acceptance</meta-name>
<meta-value>Nutritional Epidemiology</meta-value>
</custom-meta>
</custom-meta-wrap>
</article-meta>
</front>
<body>
<sec id="sec5" sec-type="intro">
<title>Introduction</title>
<p>Coronary artery disease (CAD) remains the leading cause of death worldwide, especially in patients with diabetes (<xref ref-type="bibr" rid="ref1">1</xref>, <xref ref-type="bibr" rid="ref2">2</xref>). Since CAD is responsible for more than 50% of diabetes-related mortality, it dictates the prognosis for diabetic patients (<xref ref-type="bibr" rid="ref3">3</xref>). Therefore, the 2019 European Society of Cardiology (ESC) guidelines have clarified the importance of preventing CAD in patients with diabetes (<xref ref-type="bibr" rid="ref4">4</xref>).</p>
<p>Growing evidence from observational studies and randomized controlled trials (RCTs) indicated that essential micronutrients may play a critical role in the development of CAD in people with diabetes, but the results were inconsistent (<xref ref-type="bibr" rid="ref5 ref6 ref7">5&#x2013;7</xref>). For example, a meta-analysis including 40 prospective cohort studies with over 1 million individuals has shown that increasing dietary magnesium intake was associated with a reduced risk of diabetes and all-cause mortality, but not CAD or total cardiovascular diseases (CVDs) (<xref ref-type="bibr" rid="ref8">8</xref>). Observational studies found the negative or no association between selenium biomarkers and CAD (<xref ref-type="bibr" rid="ref9">9</xref>, <xref ref-type="bibr" rid="ref10">10</xref>), however, the RCTs revealed that decreased heart disease mortality among individuals with diabetes was related to increased selenium concentration (<xref ref-type="bibr" rid="ref11">11</xref>). On the one hand, as observational studies based on reports of participants were subjected to confounding factors, which might be inaccurate leading to biased results (<xref ref-type="bibr" rid="ref12">12</xref>). On the other hand, due to the limits of the sample size, the evidence from RCTs may not be powerful enough to evaluate the causal effect of micronutrients on the risk of CAD in diabetic patients (<xref ref-type="bibr" rid="ref13">13</xref>).</p>
<p>Mendelian randomization (MR) approach can be applied to explore the potential causal association between exposure and disease by using genetic variants as instrumental variables (IVs) (<xref ref-type="bibr" rid="ref14">14</xref>). The constraints of observational studies are successfully resolved by the random assignment of genotype at conception and the non-influence of genetic variations by potential confounding variables (<xref ref-type="bibr" rid="ref15">15</xref>). In the current study, a two-sample MR analysis was conducted to investigate the causal associations between the risk of CAD in diabetic patients and circulating concentrations of six systematically selected micronutrients, including phosphorus, magnesium, selenium, iron, zinc, and copper.</p>
</sec>
<sec id="sec6" sec-type="methods">
<title>Methods</title>
<sec id="sec7">
<title>Study design</title>
<p>A two-sample MR analysis was designed to estimate the causal relationship between genetically determined circulating micronutrient concentrations and the risk of CAD in diabetic patients (<xref rid="fig1" ref-type="fig">Figure 1</xref>). The following three core assumptions should be met by the single nucleotide polymorphisms (SNPs) chosen as IVs for circulating concentrations of micronutrients: (1) IVs should be closely related to the circulating concentrations of micronutrients, (2) IVs should be independent of any potential confounders, and (3) IVs should be associated with the risk of CAD in patients with diabetes only through the concentrations of micronutrients.</p>
<fig position="float" id="fig1">
<label>Figure 1</label>
<caption>
<p>Design of the current two-sample Mendelian randomization study. Three core assumptions were as follows: (&#x03B1;) Relevance assumption; (&#x03B2;) Independence assumption; (&#x03B3;) Exclusion restriction. IVs, instrumental variables; CAD, coronary artery disease.</p>
</caption>
<graphic xlink:href="fnut-10-1103330-g001.tif"/>
</fig>
</sec>
<sec id="sec8">
<title>Genetic instrument selection</title>
<p>First, SNPs were obtained from recently published genome-wide association studies (GWASs) that independently affect these nutrient concentrations at the genome-wide significance level (<italic>p</italic>&#x2009;&#x003C;&#x2009;5&#x2009;&#x00D7;&#x2009;10<sup>&#x2212;8</sup>). Then, the linkage disequilibrium tests were performed based on the European 1000 Genomes Project reference panel (<italic>r</italic><sup>2</sup>&#x2009;&#x003C;&#x2009;0.01). If two SNPs were in linkage disequilibrium, the one with smaller value of <italic>p</italic> would be kept. Considering palindromic SNPs, those with minor allele frequency larger than 0.42 were regarded as not inferable and removed. Specifically, SNPs linked to serum phosphorus levels were extracted from a large GWAS meta-analysis including 16,264 participants of European ancestry (<xref ref-type="bibr" rid="ref16">16</xref>). Six SNPs that achieved genome-wide significance in the joint analysis of the discovery (<italic>n</italic>&#x2009;=&#x2009;15,366 participants) and replication (<italic>n</italic>&#x2009;=&#x2009;8,463 participants) cohorts from European descent were utilized as genetic IVs for serum magnesium concentration (<xref ref-type="bibr" rid="ref17">17</xref>). The GWAS meta-analysis of log-transformed toenail selenium concentrations and standardized residuals of log-transformed blood selenium concentrations, which included up to 4,162 individuals in four United States studies, provided the genetic summary data for serum selenium levels (<xref ref-type="bibr" rid="ref18">18</xref>). The genetic association with serum iron levels was derived from the Genetics of Iron Status consortium, with up to 48,972 participants (<xref ref-type="bibr" rid="ref19">19</xref>). The GWAS meta-analysis employing two cohorts from Australia and the United Kingdom yielded the SNPs chosen as genetic IVs for zinc and copper concentrations (<xref ref-type="bibr" rid="ref20">20</xref>).</p>
</sec>
<sec id="sec9">
<title>Data for outcome</title>
<p>The summary statistics for CAD in patients with diabetes were extracted from the recently published GWAS, including 15,666 patients of European ancestry with diabetes (3,968 CAD cases and 11,696 controls) from the United Kingdom Biobank (<xref ref-type="bibr" rid="ref21">21</xref>). The average age at diabetes diagnosis was 52.4&#x2009;&#x00B1;&#x2009;12.2 for CAD cases (Male: 2,936; 74.0%) and it was 51.2&#x2009;&#x00B1;&#x2009;12.6 for controls (Male: 7,037; 60.2%). The average age at visit was 62.7&#x2009;&#x00B1;&#x2009;5.6 and 60.2&#x2009;&#x00B1;&#x2009;7.0 for individuals with or without CAD, respectively.</p>
<p>All of the studies in our analyses have obtained relevant ethics review approvals, and all the participants included in the original studies provided written informed permission. All the data used in the current study had been publicly available.</p>
</sec>
<sec id="sec10">
<title>Statistical analysis</title>
<p>The multiplicative random-effects inverse-variance weighted (IVW) method was employed as the primary analysis to evaluate the effect of genetically predicted micronutrient concentrations on the risk of CAD in diabetic individuals. Specifically, the causal estimate for each SNP was generated using the Wald estimator, and the corresponding standard error was calculated using the Delta method. Subsequently, the overall estimate was calculated by meta-analyzing all the estimates by the IVW method (<xref ref-type="bibr" rid="ref22">22</xref>).</p>
<p>To further validate the accuracy of the findings, the Maximum likelihood (<xref ref-type="bibr" rid="ref22">22</xref>), Weighted median (<xref ref-type="bibr" rid="ref23">23</xref>), MR-Egger regression (<xref ref-type="bibr" rid="ref24">24</xref>), and Mendelian Randomization Pleiotropy Residual Sum and Outlier (MR-PRESSO) methods were applied in follow-up sensitivity analyses (<xref ref-type="bibr" rid="ref25">25</xref>). For instance, the Maximum likelihood method could provide a greater empirical power of estimates as it assumed that the genetic association between risk factors and outcomes follows a bivariate normal distribution (<xref ref-type="bibr" rid="ref22">22</xref>). The Weighted median method could still produce reliable estimates even if &#x2264;50% of the weight comes from the ineffective SNPs (<xref ref-type="bibr" rid="ref23">23</xref>). Intercept tests could be used in the MR-Egger regression to assess the potential horizontal pleiotropy (<xref ref-type="bibr" rid="ref24">24</xref>). The MR-PRESSO method was conducted to identify potential outliers and, after eliminating them, to provide relatively unbiased causal estimates (<xref ref-type="bibr" rid="ref25">25</xref>). In addition, scatter plots and leave-one-out analyses were performed to depict the associations of genetically determined micronutrient levels with CAD in patients with diabetes. However, sensitivity analyses and leave-one-out analyses could not be performed as the number of SNPs for zinc and copper was less than three. Cochran&#x2019;s <italic>Q</italic> statistics and corresponding value of <italic>p</italic> were calculated to assess the degree of heterogeneity in the IVW analyses (<xref ref-type="bibr" rid="ref26">26</xref>). Considering the Bonferroni adjustment for multiple tests, a value of <italic>p</italic> of &#x003C;0.008 (0.05/6 exposures) was deemed statistically significant. The value of <italic>p</italic>s between 0.008 and 0.05 were considered to indicate suggested associations. All the statistical analyses were conducted by R Software (version 4.1.1.; R Foundation for Statistical Computing, Vienna, Austria), the R package TwoSampleMR,<xref rid="fn0004" ref-type="fn"><sup>1</sup></xref> and MR-PRESSO.<xref rid="fn0005" ref-type="fn"><sup>2</sup></xref></p>
</sec>
</sec>
<sec id="sec11" sec-type="results">
<title>Results</title>
<p>Two to seven SNPs genetically determining the serum phosphorus levels were identified as IVs for serum phosphorus, magnesium, selenium, iron, zinc, and copper levels, respectively (<xref rid="tab1" ref-type="table">Table 1</xref>). In the MR analysis, all <italic>F</italic>-statistic values of the genetic tools were above the suggested threshold of 10 (<xref rid="tab1" ref-type="table">Table 1</xref>).</p>
<table-wrap position="float" id="tab1">
<label>Table 1</label>
<caption>
<p>Characteristics of the single-nucleotide polymorphisms associated with serum micronutrients levels and coronary artery disease in patients with diabetes.</p>
</caption>
<table frame="hsides" rules="groups">
<thead>
<tr>
<th align="left" valign="top" rowspan="2">Exposure</th>
<th align="center" valign="top" rowspan="2">SNP</th>
<th align="center" valign="top" rowspan="2">Chr</th>
<th align="center" valign="top" rowspan="2">Pos</th>
<th align="center" valign="top" rowspan="2">EA</th>
<th align="center" valign="top" rowspan="2">OA</th>
<th align="center" valign="top" rowspan="2">EAF</th>
<th align="center" valign="top" rowspan="2"><italic>F</italic></th>
<th align="center" valign="top" colspan="3">Micronutrients</th>
<th align="center" valign="top" colspan="3">CAD in patients with diabetes</th>
</tr>
<tr>
<th align="center" valign="top">Beta</th>
<th align="center" valign="top">SE</th>
<th align="center" valign="top"><italic>p</italic> value</th>
<th align="center" valign="top">Beta</th>
<th align="center" valign="top">SE</th>
<th align="center" valign="top"><italic>p</italic> value</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" valign="middle">Phosphorus</td>
<td align="center" valign="middle">rs1697421</td>
<td align="center" valign="middle">1</td>
<td align="center" valign="middle">21,823,292</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">0.49</td>
<td align="center" valign="middle">100</td>
<td align="center" valign="middle">0.050</td>
<td align="center" valign="middle">0.005</td>
<td align="center" valign="middle">1.14E&#x2212;27</td>
<td align="center" valign="middle">0.033</td>
<td align="center" valign="middle">0.027</td>
<td align="center" valign="middle">0.217</td>
</tr>
<tr>
<td align="left" valign="middle">Phosphorus</td>
<td align="center" valign="middle">rs17265703</td>
<td align="center" valign="middle">3</td>
<td align="center" valign="middle">122,048,644</td>
<td align="center" valign="middle">G</td>
<td align="center" valign="middle">A</td>
<td align="center" valign="middle">0.85</td>
<td align="center" valign="middle">36</td>
<td align="center" valign="middle">0.036</td>
<td align="center" valign="middle">0.006</td>
<td align="center" valign="middle">4.32E&#x2212;09</td>
<td align="center" valign="middle">0.042</td>
<td align="center" valign="middle">0.038</td>
<td align="center" valign="middle">0.259</td>
</tr>
<tr>
<td align="left" valign="middle">Phosphorus</td>
<td align="center" valign="middle">rs9469578</td>
<td align="center" valign="middle">6</td>
<td align="center" valign="middle">33,706,479</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">0.92</td>
<td align="center" valign="middle">43</td>
<td align="center" valign="middle">0.059</td>
<td align="center" valign="middle">0.009</td>
<td align="center" valign="middle">1.11E&#x2212;11</td>
<td align="center" valign="middle">&#x2212;0.021</td>
<td align="center" valign="middle">0.052</td>
<td align="center" valign="middle">0.684</td>
</tr>
<tr>
<td align="left" valign="middle">Phosphorus</td>
<td align="center" valign="middle">rs947583</td>
<td align="center" valign="middle">6</td>
<td align="center" valign="middle">136,133,659</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">0.29</td>
<td align="center" valign="middle">49</td>
<td align="center" valign="middle">0.035</td>
<td align="center" valign="middle">0.005</td>
<td align="center" valign="middle">3.45E&#x2212;12</td>
<td align="center" valign="middle">0.036</td>
<td align="center" valign="middle">0.030</td>
<td align="center" valign="middle">0.224</td>
</tr>
<tr>
<td align="left" valign="middle">Phosphorus</td>
<td align="center" valign="middle">rs2970818</td>
<td align="center" valign="middle">12</td>
<td align="center" valign="middle">4,606,168</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">A</td>
<td align="center" valign="middle">0.09</td>
<td align="center" valign="middle">35</td>
<td align="center" valign="middle">0.047</td>
<td align="center" valign="middle">0.008</td>
<td align="center" valign="middle">4.38E&#x2212;09</td>
<td align="center" valign="middle">&#x2212;0.029</td>
<td align="center" valign="middle">0.044</td>
<td align="center" valign="middle">0.510</td>
</tr>
<tr>
<td align="left" valign="middle">Magnesium</td>
<td align="center" valign="middle">rs11144134</td>
<td align="center" valign="middle">9</td>
<td align="center" valign="middle">77,499,796</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">0.08</td>
<td align="center" valign="middle">121</td>
<td align="center" valign="middle">0.011</td>
<td align="center" valign="middle">0.001</td>
<td align="center" valign="middle">8.20E&#x2212;15</td>
<td align="center" valign="middle">0.062</td>
<td align="center" valign="middle">0.048</td>
<td align="center" valign="middle">0.191</td>
</tr>
<tr>
<td align="left" valign="middle">Magnesium</td>
<td align="center" valign="middle">rs13146355</td>
<td align="center" valign="middle">4</td>
<td align="center" valign="middle">77,412,140</td>
<td align="center" valign="middle">A</td>
<td align="center" valign="middle">G</td>
<td align="center" valign="middle">0.44</td>
<td align="center" valign="middle">25</td>
<td align="center" valign="middle">0.005</td>
<td align="center" valign="middle">0.001</td>
<td align="center" valign="middle">6.30E&#x2212;13</td>
<td align="center" valign="middle">0.033</td>
<td align="center" valign="middle">0.027</td>
<td align="center" valign="middle">0.220</td>
</tr>
<tr>
<td align="left" valign="middle">Magnesium</td>
<td align="center" valign="middle">rs3925584</td>
<td align="center" valign="middle">11</td>
<td align="center" valign="middle">30,760,335</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">0.55</td>
<td align="center" valign="middle">36</td>
<td align="center" valign="middle">0.006</td>
<td align="center" valign="middle">0.001</td>
<td align="center" valign="middle">5.20E&#x2212;16</td>
<td align="center" valign="middle">0.007</td>
<td align="center" valign="middle">0.027</td>
<td align="center" valign="middle">0.791</td>
</tr>
<tr>
<td align="left" valign="middle">Magnesium</td>
<td align="center" valign="middle">rs4072037</td>
<td align="center" valign="middle">1</td>
<td align="center" valign="middle">155,162,067</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">0.54</td>
<td align="center" valign="middle">100</td>
<td align="center" valign="middle">0.010</td>
<td align="center" valign="middle">0.001</td>
<td align="center" valign="middle">2.00E&#x2212;36</td>
<td align="center" valign="middle">0.012</td>
<td align="center" valign="middle">0.027</td>
<td align="center" valign="middle">0.640</td>
</tr>
<tr>
<td align="left" valign="middle">Magnesium</td>
<td align="center" valign="middle">rs448378</td>
<td align="center" valign="middle">3</td>
<td align="center" valign="middle">169,100,899</td>
<td align="center" valign="middle">A</td>
<td align="center" valign="middle">G</td>
<td align="center" valign="middle">0.53</td>
<td align="center" valign="middle">16</td>
<td align="center" valign="middle">0.004</td>
<td align="center" valign="middle">0.001</td>
<td align="center" valign="middle">1.30E&#x2212;08</td>
<td align="center" valign="middle">0.019</td>
<td align="center" valign="middle">0.027</td>
<td align="center" valign="middle">0.471</td>
</tr>
<tr>
<td align="left" valign="middle">Selenium</td>
<td align="center" valign="middle">rs921943</td>
<td align="center" valign="middle">5</td>
<td align="center" valign="middle">79,020,653</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">0.29</td>
<td align="center" valign="middle">119</td>
<td align="center" valign="middle">0.250</td>
<td align="center" valign="middle">0.020</td>
<td align="center" valign="middle">1.90E&#x2212;39</td>
<td align="center" valign="middle">0.069</td>
<td align="center" valign="middle">0.029</td>
<td align="center" valign="middle">0.019</td>
</tr>
<tr>
<td align="left" valign="middle">Selenium</td>
<td align="center" valign="middle">rs567754</td>
<td align="center" valign="middle">5</td>
<td align="center" valign="middle">79,120,593</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">0.67</td>
<td align="center" valign="middle">67</td>
<td align="center" valign="middle">0.170</td>
<td align="center" valign="middle">0.020</td>
<td align="center" valign="middle">8.40E&#x2212;20</td>
<td align="center" valign="middle">0.056</td>
<td align="center" valign="middle">0.028</td>
<td align="center" valign="middle">0.048</td>
</tr>
<tr>
<td align="left" valign="middle">Selenium</td>
<td align="center" valign="middle">rs3797535</td>
<td align="center" valign="middle">5</td>
<td align="center" valign="middle">79,004,574</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">0.10</td>
<td align="center" valign="middle">36</td>
<td align="center" valign="middle">0.210</td>
<td align="center" valign="middle">0.040</td>
<td align="center" valign="middle">2.10E&#x2212;15</td>
<td align="center" valign="middle">&#x2212;0.011</td>
<td align="center" valign="middle">0.049</td>
<td align="center" valign="middle">0.816</td>
</tr>
<tr>
<td align="left" valign="middle">Selenium</td>
<td align="center" valign="middle">rs11951068</td>
<td align="center" valign="middle">5</td>
<td align="center" valign="middle">79,008,491</td>
<td align="center" valign="middle">A</td>
<td align="center" valign="middle">G</td>
<td align="center" valign="middle">0.06</td>
<td align="center" valign="middle">31</td>
<td align="center" valign="middle">0.210</td>
<td align="center" valign="middle">0.040</td>
<td align="center" valign="middle">1.90E&#x2212;11</td>
<td align="center" valign="middle">0.076</td>
<td align="center" valign="middle">0.051</td>
<td align="center" valign="middle">0.137</td>
</tr>
<tr>
<td align="left" valign="middle">Selenium</td>
<td align="center" valign="middle">rs705415</td>
<td align="center" valign="middle">5</td>
<td align="center" valign="middle">78,996,137</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">0.88</td>
<td align="center" valign="middle">39</td>
<td align="center" valign="middle">0.230</td>
<td align="center" valign="middle">0.040</td>
<td align="center" valign="middle">4.60E&#x2212;10</td>
<td align="center" valign="middle">&#x2212;0.008</td>
<td align="center" valign="middle">0.042</td>
<td align="center" valign="middle">0.841</td>
</tr>
<tr>
<td align="left" valign="middle">Selenium</td>
<td align="center" valign="middle">rs6586282</td>
<td align="center" valign="middle">21</td>
<td align="center" valign="middle">43,058,387</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">0.85</td>
<td align="center" valign="middle">21</td>
<td align="center" valign="middle">0.120</td>
<td align="center" valign="middle">0.030</td>
<td align="center" valign="middle">4.00E&#x2212;09</td>
<td align="center" valign="middle">&#x2212;0.046</td>
<td align="center" valign="middle">0.035</td>
<td align="center" valign="middle">0.194</td>
</tr>
<tr>
<td align="left" valign="middle">Selenium</td>
<td align="center" valign="middle">rs1789953</td>
<td align="center" valign="middle">21</td>
<td align="center" valign="middle">43,062,826</td>
<td align="center" valign="middle">T</td>
<td align="center" valign="middle">C</td>
<td align="center" valign="middle">0.16</td>
<td align="center" valign="middle">17</td>
<td align="center" valign="middle">0.120</td>
<td align="center" valign="middle">0.030</td>
<td align="center" valign="middle">3.40E&#x2212;08</td>
<td align="center" valign="middle">0.041</td>
<td align="center" valign="middle">0.040</td>
<td align="center" valign="middle">0.301</td>
</tr>
<tr>
<td align="left" valign="middle">Iron</td>
<td align="center" valign="middle">rs1800562</td>
<td align="center" valign="top">6</td>
<td align="center" valign="top">26,093,141</td>
<td align="center" valign="top">A</td>
<td align="center" valign="top">G</td>
<td align="center" valign="top">0.07</td>
<td align="center" valign="top">696</td>
<td align="center" valign="top">0.328</td>
<td align="center" valign="top">0.016</td>
<td align="center" valign="top">2.70E&#x2212;97</td>
<td align="center" valign="top">&#x2212;0.054</td>
<td align="center" valign="top">0.049</td>
<td align="center" valign="top">0.268</td>
</tr>
<tr>
<td align="left" valign="top">Iron</td>
<td align="center" valign="top">rs1799945</td>
<td align="center" valign="top">6</td>
<td align="center" valign="top">26,091,179</td>
<td align="center" valign="top">C</td>
<td align="center" valign="top">G</td>
<td align="center" valign="top">0.15</td>
<td align="center" valign="top">450</td>
<td align="center" valign="top">&#x2212;0.189</td>
<td align="center" valign="top">0.010</td>
<td align="center" valign="top">1.10E&#x2212;81</td>
<td align="center" valign="top">0.069</td>
<td align="center" valign="top">0.038</td>
<td align="center" valign="top">0.067</td>
</tr>
<tr>
<td align="left" valign="top">Iron</td>
<td align="center" valign="top">rs855791</td>
<td align="center" valign="top">22</td>
<td align="center" valign="top">37,462,936</td>
<td align="center" valign="top">A</td>
<td align="center" valign="top">G</td>
<td align="center" valign="top">0.55</td>
<td align="center" valign="top">807</td>
<td align="center" valign="top">&#x2212;0.181</td>
<td align="center" valign="top">0.007</td>
<td align="center" valign="top">1.30E&#x2212;139</td>
<td align="center" valign="top">0.028</td>
<td align="center" valign="top">0.027</td>
<td align="center" valign="top">0.299</td>
</tr>
<tr>
<td align="left" valign="top">Iron</td>
<td align="center" valign="top">rs8177240</td>
<td align="center" valign="top">3</td>
<td align="center" valign="top">133,477,701</td>
<td align="center" valign="top">T</td>
<td align="center" valign="top">G</td>
<td align="center" valign="top">0.67</td>
<td align="center" valign="top">95</td>
<td align="center" valign="top">&#x2212;0.066</td>
<td align="center" valign="top">0.007</td>
<td align="center" valign="top">6.70E&#x2212;20</td>
<td align="center" valign="top">0.005</td>
<td align="center" valign="top">0.028</td>
<td align="center" valign="top">0.860</td>
</tr>
<tr>
<td align="left" valign="top">Iron</td>
<td align="center" valign="top">rs7385804</td>
<td align="center" valign="top">7</td>
<td align="center" valign="top">100,235,970</td>
<td align="center" valign="top">A</td>
<td align="center" valign="top">C</td>
<td align="center" valign="top">0.62</td>
<td align="center" valign="top">95</td>
<td align="center" valign="top">0.064</td>
<td align="center" valign="top">0.007</td>
<td align="center" valign="top">1.40E&#x2212;18</td>
<td align="center" valign="top">&#x2212;0.003</td>
<td align="center" valign="top">0.028</td>
<td align="center" valign="top">0.918</td>
</tr>
<tr>
<td align="left" valign="top">Zinc</td>
<td align="center" valign="top">rs2120019</td>
<td align="center" valign="top">15</td>
<td align="center" valign="top">75,334,184</td>
<td align="center" valign="top">T</td>
<td align="center" valign="top">C</td>
<td align="center" valign="top">0.79</td>
<td align="center" valign="top">75</td>
<td align="center" valign="top">0.287</td>
<td align="center" valign="top">0.033</td>
<td align="center" valign="top">1.60E&#x2212;18</td>
<td align="center" valign="top">0.021</td>
<td align="center" valign="top">0.034</td>
<td align="center" valign="top">0.537</td>
</tr>
<tr>
<td align="left" valign="top">Zinc</td>
<td align="center" valign="top">rs1532423</td>
<td align="center" valign="top">8</td>
<td align="center" valign="top">86,268,313</td>
<td align="center" valign="top">A</td>
<td align="center" valign="top">G</td>
<td align="center" valign="top">0.37</td>
<td align="center" valign="top">47</td>
<td align="center" valign="top">0.178</td>
<td align="center" valign="top">0.026</td>
<td align="center" valign="top">6.40E&#x2212;12</td>
<td align="center" valign="top">&#x2212;0.006</td>
<td align="center" valign="top">0.027</td>
<td align="center" valign="top">0.811</td>
</tr>
<tr>
<td align="left" valign="top">Copper</td>
<td align="center" valign="top">rs1175550</td>
<td align="center" valign="top">1</td>
<td align="center" valign="top">3,691,528</td>
<td align="center" valign="top">G</td>
<td align="center" valign="top">A</td>
<td align="center" valign="top">0.22</td>
<td align="center" valign="top">38</td>
<td align="center" valign="top">0.198</td>
<td align="center" valign="top">0.032</td>
<td align="center" valign="top">5.00E&#x2212;10</td>
<td align="center" valign="top">0.003</td>
<td align="center" valign="top">0.032</td>
<td align="center" valign="top">0.922</td>
</tr>
<tr>
<td align="left" valign="top">Copper</td>
<td align="center" valign="top">rs2769264</td>
<td align="center" valign="top">1</td>
<td align="center" valign="top">151,344,741</td>
<td align="center" valign="top">G</td>
<td align="center" valign="top">T</td>
<td align="center" valign="top">0.16</td>
<td align="center" valign="top">85</td>
<td align="center" valign="top">0.313</td>
<td align="center" valign="top">0.034</td>
<td align="center" valign="top">2.60E&#x2212;20</td>
<td align="center" valign="top">0.006</td>
<td align="center" valign="top">0.034</td>
<td align="center" valign="top">0.866</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<p>SNP, single-nucleotide polymorphism; Chr, chromosome; Pos, position; EA, effect allele; OA, other allele; EAF, frequency of effect allele; F, F-statistics; SE, standard error; and CAD, coronary artery disease.</p>
</table-wrap-foot>
</table-wrap>
<p>The primary findings of MR studies of genetically predicted circulation concentrations of micronutrients with the risk of CAD in individuals with diabetes were displayed in <xref rid="fig2" ref-type="fig">Figure 2</xref>. The random-effects IVW results indicated that genetically predisposition to one standard deviation increase in concentrations of serum copper, selenium, and magnesium was linked to 2% (odds ratio [OR], 1.02; 95% CI, 1.02&#x2013;1.02 <italic>p</italic>&#x2009;=&#x2009;3.75&#x2009;&#x00D7;&#x2009;10<sup>&#x2212;49</sup>), 25% (OR, 1.25; 95% CI, 1.10&#x2013;1.42; <italic>p</italic>&#x2009;=&#x2009;5.01&#x2009;&#x00D7;&#x2009;10<sup>&#x2212;4</sup>), and 41% (OR, 1.41; 95% CI, 1.14&#x2013;1.73; <italic>p</italic>&#x2009;=&#x2009;1.25&#x2009;&#x00D7;&#x2009;10<sup>&#x2212;3</sup>) higher risk of CAD in diabetic patients, respectively (<xref rid="fig2" ref-type="fig">Figure 2</xref>). An 18% (OR, 0.82; 95% CI, 0.75&#x2013;0.90, <italic>p</italic>&#x2009;=&#x2009;2.16&#x2009;&#x00D7;&#x2009;10<sup>&#x2212;5</sup>) reduced risk of CAD was observed in patients with diabetes when the genetically predicted serum iron content increase by one standard deviation (<xref rid="fig2" ref-type="fig">Figure 2</xref>). There was minimal proof that circulating concentrations of phosphorus and zinc were associated with the risk of CAD in patients with diabetes (<xref rid="fig2" ref-type="fig">Figure 2</xref>). The scatter plots also visually depicted the associations between micronutrients and CAD in diabetic patients (<xref ref-type="supplementary-material" rid="SM1">Supplementary Figures 1</xref>&#x2013;<xref ref-type="supplementary-material" rid="SM1">6</xref>).</p>
<fig position="float" id="fig2">
<label>Figure 2</label>
<caption>
<p>Mendelian randomization association of genetically predicted serum micronutrients levels with coronary artery disease in patients with diabetes using different statistical models. OR, odds ratio; CI, confidence interval; IVW, inverse-variance weighted method; MR, Mendelian randomization; and MR-PRESSO, MR-pleiotropy residual sum and outlier.</p>
</caption>
<graphic xlink:href="fnut-10-1103330-g002.tif"/>
</fig>
<p>The association patterns of phosphorus, selenium, and iron based on sensitivity analyses were consistent with the IVW MR analyses, but not magnesium (<xref rid="fig2" ref-type="fig">Figure 2</xref>). In addition, stable correlations were found in the MR-PRESSO analysis of serum phosphorus (OR, 1.56; 95% CI, 0.84&#x2013;2.90; <italic>p</italic>&#x2009;=&#x2009;0.23), serum magnesium (OR, 1.34; 95% CI, 1.08&#x2013;1.66; <italic>p</italic>&#x2009;=&#x2009;0.05), serum selenium (OR, 1.25; 95% CI, 1.10&#x2013;1.42; <italic>p</italic>&#x2009;=&#x2009;0.01), and serum iron (OR, 0.82; 95% CI, 0.75&#x2013;0.90; <italic>p</italic>&#x2009;=&#x2009;0.01) with no outliers were revealed (<xref rid="fig2" ref-type="fig">Figure 2</xref>). Between the estimates of chosen SNPs, no evidence of heterogeneity for the relationships between micronutrients and CAD in diabetic patients was observed, and neither the MR-Egger intercept test nor the Cochrane&#x2019;s <italic>Q</italic> test indicated any possible directional pleiotropy (all <italic>p</italic>&#x2009;&#x003E;&#x2009;0.05; <xref rid="tab2" ref-type="table">Table 2</xref>). Leave-one-out analyses suggested that no single SNP significantly influenced the effect of serum micronutrient levels on CAD in diabetic patients (<xref ref-type="supplementary-material" rid="SM1">Supplementary Figures 7</xref>&#x2013;<xref ref-type="supplementary-material" rid="SM1">10</xref>).</p>
<table-wrap position="float" id="tab2">
<label>Table 2</label>
<caption>
<p>Heterogeneity and pleiotropy tests for the associations of micronutrients with coronary artery disease in patients with diabetes.</p>
</caption>
<table frame="hsides" rules="groups">
<thead>
<tr>
<th align="left" valign="top">Micronutrients</th>
<th align="center" valign="top">Q value</th>
<th align="center" valign="top"><italic>p</italic><sub>Q</sub></th>
<th align="center" valign="top">MR-Egger intercept</th>
<th align="center" valign="top"><italic>p</italic><sub>intercept</sub></th>
</tr>
</thead>
<tbody>
<tr>
<td align="left" valign="middle">Phosphorus</td>
<td align="center" valign="middle">3.26</td>
<td align="center" valign="middle">0.516</td>
<td align="center" valign="middle">0.100</td>
<td align="center" valign="middle">0.324</td>
</tr>
<tr>
<td align="left" valign="middle">Magnesium</td>
<td align="center" valign="middle">1.48</td>
<td align="center" valign="middle">0.830</td>
<td align="center" valign="middle">0.016</td>
<td align="center" valign="middle">0.691</td>
</tr>
<tr>
<td align="left" valign="middle">Selenium</td>
<td align="center" valign="middle">4.78</td>
<td align="center" valign="middle">0.572</td>
<td align="center" valign="middle">0.044</td>
<td align="center" valign="middle">0.454</td>
</tr>
<tr>
<td align="left" valign="middle">Iron</td>
<td align="center" valign="middle">1.03</td>
<td align="center" valign="middle">0.905</td>
<td align="center" valign="middle">0.009</td>
<td align="center" valign="middle">0.761</td>
</tr>
<tr>
<td align="left" valign="middle">Zinc</td>
<td align="center" valign="middle">0.32</td>
<td align="center" valign="middle">0.570</td>
<td align="center" valign="middle">NA</td>
<td align="center" valign="middle">NA</td>
</tr>
<tr>
<td align="left" valign="middle">Copper</td>
<td align="center" valign="middle">1.76E-04</td>
<td align="center" valign="middle">0.989</td>
<td align="center" valign="middle">NA</td>
<td align="center" valign="middle">NA</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<p>MR, Mendelian randomization; NA, not available.</p>
</table-wrap-foot>
</table-wrap>
</sec>
<sec id="sec12" sec-type="discussions">
<title>Discussion</title>
<p>In this comprehensive MR analysis, genetic data from the largest published GWAS were leveraged to evaluate the relationship between genetic susceptibility to six micronutrients and the risk of CAD in diabetic patients. We provided consistent evidence that circulating selenium concentrations were genetically expected to be related with a higher risk of CAD, whereas iron concentrations were associated with a lower risk of CAD in patients with diabetes. The association pattern remained consistent when repeated in the majority of supplementary analyses. However, there was limited evidence to link the risk of CAD in diabetic patients with circulating levels of magnesium, phosphorus, zinc, and copper.</p>
<sec id="sec13">
<title>Selenium and CAD in patients with diabetes</title>
<p>According to the previous observational studies and RCTs, the association between selenium and CAD in patients with diabetes was inconsistent (<xref ref-type="bibr" rid="ref11">11</xref>, <xref ref-type="bibr" rid="ref27">27</xref>, <xref ref-type="bibr" rid="ref28">28</xref>). A prospective study involving 3,897 diabetes in the Dongfeng-Tongji cohort suggested an inverse association between plasma levels of selenium and risk of cardiovascular diseases (CVDs) in patients with diabetes (<xref ref-type="bibr" rid="ref29">29</xref>). Selenium supplementation was not sufficient however, to reduce CAD mortality, according to the findings from a meta-analysis that included 16 RCTs (<xref ref-type="bibr" rid="ref30">30</xref>). Additionally, previous observational studies have reported no difference in circulating selenium concentrations between diabetic patients with and without CAD (<xref ref-type="bibr" rid="ref27">27</xref>). A positive association of selenium with diabetes was found in previous observational studies (<xref ref-type="bibr" rid="ref31 ref32 ref33">31&#x2013;33</xref>), several RCTs (<xref ref-type="bibr" rid="ref34 ref35 ref36">34&#x2013;36</xref>), and a MR study (<xref ref-type="bibr" rid="ref37">37</xref>). Numerous <italic>in vitro</italic> and animal investigations have revealed the mechanism for how selenium increases the risk of diabetes and CAD. As a member of the glutathione peroxidase (GPx) family, selenium serves as the center of redox (<xref ref-type="bibr" rid="ref38">38</xref>). Transgenic animal models have found increased GPx1 expression interferes with insulin signaling by removing hydrogen peroxide, leading to the development of insulin resistance, hyperglycemia, and obesity (<xref ref-type="bibr" rid="ref39">39</xref>, <xref ref-type="bibr" rid="ref40">40</xref>). Selenoprotein P (SelP), a selenium-supply protein, is hypothesized to raise the risk of diabetes by promoting insulin resistance and dysregulating glucose metabolism (<xref ref-type="bibr" rid="ref41">41</xref>). In addition, Selk, a selenoprotein of the endoplasmic reticulum membrane, contribute to foam cell formation and atherogenesis by stabilizing expression of CD36 in macrophages during inflammation (<xref ref-type="bibr" rid="ref42">42</xref>, <xref ref-type="bibr" rid="ref43">43</xref>). According to the results of our MR investigation, selenium may be associated in a directionally consistent manner with CAD in patients with diabetes. Given that diabetes is a known risk factor for CAD, this conclusion might seem intuitive. However, considering the majority of the individuals covered with this research were of European origin, the generalizability of our findings to other groups needs to be further investigated. The inverse association between levels of selenium and CVDs risk in Asian diabetic may due to the difference of dietary structure, lifestyle and genetic predisposition.</p>
</sec>
<sec id="sec14">
<title>Iron and CAD in patients with diabetes</title>
<p>An inverse association between iron concentration and CAD in diabetic patients was observed in our MR analysis. A two-sample MR approach examining serum iron status for CAD risk in the general population revealed that serum iron concentration was linked to a lower chance of developing CAD (OR, 0.94; 95%CI, 0.88&#x2013;1.00; <italic>p</italic>&#x2009;=&#x2009;0.039), which is consistent with our findings in the diabetic population (<xref ref-type="bibr" rid="ref44">44</xref>). In addition, a recent two-sample MR study based on the data from United Kingdom Biobank discovered that high levels of iron status were protective against coronary atherosclerosis in the male population (<xref ref-type="bibr" rid="ref45">45</xref>). Furthermore, a meta-analysis of prospective studies involving 156,427 participants showed a negative association between serum iron and risk of coronary heart disease after excluding the study by Morrisson et al. (risk ratio [RR], 0.80; 95%CI, 0.73&#x2013;0.87) (<xref ref-type="bibr" rid="ref46">46</xref>). Numerous observational studies have also demonstrated the protective effect of iron on CAD in diabetic individuals (<xref ref-type="bibr" rid="ref47">47</xref>, <xref ref-type="bibr" rid="ref48">48</xref>). An inverse correlation between iron reserves and cardiovascular disease in patients with diabetes was reported by a cross-sectional and prospective observational study encompassing 38,671 people and 821 diabetes patients (OR, 0.81; 95%CI, 0.68&#x2013;0.96; <italic>p</italic>&#x2009;=&#x2009;0.018) (<xref ref-type="bibr" rid="ref48">48</xref>). Similarly, the results of an observational study including 424 consecutive men with type 2 diabetes mellitus showed high ferritin levels may reduce cardiovascular risk in men with diabetes (<xref ref-type="bibr" rid="ref49">49</xref>). Several plausible mechanisms have been hypothesized to elucidate the protective effect of high iron load on CAD. For instance, an animal study found that a high-iron diet attenuates atherosclerosis in mice lacking apolipoprotein E (<xref ref-type="bibr" rid="ref50">50</xref>). Similar, another recent animal study suggested that iron overload could diminish atherosclerosis in apolipoprotein E knockout mice by interfering with hepatic CD36 and fatty acid binding proteins-mediated fatty acid uptake and transport (<xref ref-type="bibr" rid="ref51">51</xref>). Furthermore, it has been proven that ferritin, a natural antioxidant, may reduce the risk of CAD in patients with diabetes by compensating for chronic systemic inflammation in diabetes (<xref ref-type="bibr" rid="ref52">52</xref>, <xref ref-type="bibr" rid="ref53">53</xref>).</p>
</sec>
<sec id="sec15">
<title>Other micronutrients and CAD in patients with diabetes</title>
<p>In the current MR study, we observed a nominally significant association between genetically predicted concentrations of magnesium and the risk of CAD in patients with diabetes, but the other four statistical models were not statistically significant. As a result, we preclude the presence of a stable causal association between serum magnesium concentration and outcome. We also observed a significant correlation between genetically predicted concentrations of copper and the risk of CAD in patients with diabetes in the main analysis; however, because there are only two genetic instruments for copper, we are unable to perform sensitivity analysis to assess the stability of the results. Meanwhile, the results of IVW (fixed effects) suggested no causal connection between copper and CAD in patients with diabetes. Thus, we are unable to tell whether there is a possible causal relationship between copper and the outcome. The results of the current MR study showed that little evidence approved the causal effects of genetically predicted concentrations of phosphorus and zinc on CAD risk in diabetic patients. There is a scarcity of observational epidemiology research on these micronutrient concentrations and the incidence of CAD in diabetic patients, and the results from the few available observational studies of the general population are inconclusive (<xref ref-type="bibr" rid="ref12">12</xref>, <xref ref-type="bibr" rid="ref54 ref55 ref56 ref57">54&#x2013;57</xref>). Thus, our results from the current MR study may imply that serum phosphorus and zinc levels should not be regarded as independent risk factors for CAD in patients with diabetes.</p>
</sec>
<sec id="sec16">
<title>Strengths and limitations</title>
<p>The design of MR study, which avoids biases frequently seen in standard observational studies and provides the non-biased causal connection between exposure and outcome, is the main merit (<xref ref-type="bibr" rid="ref58">58</xref>). Besides, our MR study uses summary-level data from the large genetic consortium to date, which allows us to more accurately formulate our study hypothesis. Meanwhile, the statistical power in the current investigation is ensured by the estimated effects (<italic>F</italic>-statistics) of each instrumental variable exceeding the threshold. Moreover, sensitivity analyses based on multiple statistical models combined with leave-one-out analyses were employed to detect the stability of the main results, which offered additional reliable evidence.</p>
<p>It is crucial to acknowledge several potential limitations when interpreting our results. First, although MR-PRESSO analysis and MR-Egger intercept tests did not reveal any evidence of pleiotropy that might have influenced our results, potential horizontal pleiotropy cannot be completely excluded. Second, the current study was based on summary-level data and lacked subgroup-specific analyses, as there are no corresponding sex- or age-specific data sets in the consortium. Third, the majority of the individuals in our MR research were of European origin, which may restrict the generalizability of the primary findings to other groups. Therefore, the corresponding results should be cautious to make the conclusion.</p>
</sec>
</sec>
<sec id="sec17" sec-type="conclusions">
<title>Conclusion</title>
<p>The current study provides genetic evidence for the possible causal effects of increased selenium and decreased iron levels on the increased risk of CAD in patients with diabetes. Diet, supplements, or other methods to modify circulating selenium and iron concentrations may be effective strategies to prevent CAD in patients with diabetes.</p>
</sec>
<sec id="sec18" sec-type="data-availability">
<title>Data availability statement</title>
<p>The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found in the article/<xref ref-type="supplementary-material" rid="SM1">Supplementary material</xref>.</p>
</sec>
<sec id="sec19">
<title>Ethics statement</title>
<p>Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. The patients/participants provided their written informed consent to participate in this study.</p>
</sec>
<sec id="sec20">
<title>Author contributions</title>
<p>MT, NH, TH, and HC designed the study and wrote the analysis plan. NH and TH undertook analyses. MT and TH wrote the first draft of the manuscript with critical revisions from NH, JY, and HC. MT, TH, JY, HC, and NH interpreted the results in the study and gave final approval of the version to be published. All authors contributed to the article and approved the submitted version.</p>
</sec>
<sec id="sec21" sec-type="funding-information">
<title>Funding</title>
<p>This work was supported by grants from the Key Laboratory of Precision Medicine for Atherosclerotic Diseases of Zhejiang Province, China (Grant No. 2022E10026), National Natural Science Foundation of China (82200489), the Major Project of Science and Technology Innovation 2025 in Ningbo, China (Grant No. 2021Z134), the Key research and development project of Zhejiang Province, China (Grant No. 2021C03096), and Public Science and Technology Projects of Ningbo (202002N3175).</p>
</sec>
<sec id="conf1" sec-type="COI-statement">
<title>Conflict of interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec id="sec100" sec-type="disclaimer">
<title>Publisher&#x2019;s note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
</body>
<back>
<ack>
<p>The authors thank all the investigators of CHARGE Consortium, GEFOS consortium, United Kingdom Biobank study, MAGIC, and GISC for providing the data publicly.</p>
</ack>
<sec id="sec23" sec-type="supplementary-material">
<title>Supplementary material</title>
<p>The Supplementary material for this article can be found online at: <ext-link xlink:href="https://www.frontiersin.org/articles/10.3389/fnut.2023.1103330/full#supplementary-material" ext-link-type="uri">https://www.frontiersin.org/articles/10.3389/fnut.2023.1103330/full#supplementary-material</ext-link></p>
<supplementary-material xlink:href="Data_Sheet_1.PDF" id="SM1" mimetype="application/pdf" xmlns:xlink="http://www.w3.org/1999/xlink"/>
</sec>
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<fn-group><fn id="fn0004"><p><sup>1</sup><ext-link xlink:href="https://github.com/MRCIEU/TwoSampleMR" ext-link-type="uri">https://github.com/MRCIEU/TwoSampleMR</ext-link></p></fn>
<fn id="fn0005"><p><sup>2</sup><ext-link xlink:href="https://github.com/rondolab/MR-PRESSO" ext-link-type="uri">https://github.com/rondolab/MR-PRESSO</ext-link></p></fn></fn-group>
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