Globally ~422 million people live with diabetes and prevalence of the condition has been increasing steadily over recent decades (1). In Europe, there are approximately 60 million people with the condition, about 10.3% of men and 9.6% of women aged 25 years and over (2). In Spain, the incidence of diabetes, adjusted for age and gender has been reported to be 11.6 cases/1,000 person-years (95%CI = 11.1-12.1) (3).

Diabetes is associated with multiple health complications. One complication is visual impairment with cataract being a key cause (4). Indeed, people with diabetes are up to five times more likely to develop cataracts compared to those without diabetes (5, 6). Both visual impairment and diabetes separately have been linked to higher levels of depression and anxiety than in the general population. For example, one meta-analysis of seven studies concluded that diabetes is associated with an increased risk of depression (7), and another showed significant positive associations with anxiety disorders (1.20; 95% CI = 1.10-1.31) and elevated anxiety symptoms (1.48; 95%CI = 1.02-1.93), with a pooled OR for all anxiety studies (1.25; 95% CI = 1.10-1.39) (8). Furthermore, another systematic review (9) and a 16-year nationwide population-based longitudinal study (10) suggested that a strong link exists between cataracts and depression. Higher levels of anxiety in people with cataracts have also been suggested (11).

Bener et al. reported that significantly more women with diabetes had depression (63.3 vs. 50.4%) and anxiety (70.1 vs. 61.6%) compared to men (12). With regards to the prevalence of depression in people with cataracts by gender, Liu et al. (13) found that there was a similar prevalence of depression in women (24.2%) and men (23.6%).

Given that diabetes and cataracts are both associated with higher risk for mental health problems, it is possible that people with co-existing diabetes and cataracts would have higher risk of depression and anxiety. In addition, although gender differences have been previously found in prevalence studies for depression and anxiety, it is not known whether gender differences exist in mental health in people who have both diabetes and cataract. Therefore, in accordance with the international recommendations about gender in public health research (14, 15), the aim of the present study was to explore gender differences in the associations between cataracts and self-reported depression and chronic anxiety in Spanish adults with diabetes.

In this self-weighting sample of 2,266 adults with diabetes residing in Spain (50.2% women; average age 69.7 ± 12.7 years, males 67.9 ± 11.9 and females 71.4 ± 13.2; age range 15-98 years, males 15-97 and females 26-98), the overall prevalence of depression was 18.4% and the prevalence of chronic anxiety was 12.3 %. The prevalence of depression among those with cataract was significantly higher than in those without cataract (24.7 vs. 15.2%). Bivariate analysis showed that the groups with the following characteristics had the highest levels of depression: women, ≥65 years, people not married, people not living as a couple, ≤ primary education, people who never smoked, non-alcohol drinkers, obesity, <600 MET-min/week of physical activity. For chronic anxiety groups the following characteristics had the highest levels of chronic anxiety: women, <65 years, not married or not living as a couple, secondary education, current smokers, non-alcohol drinkers, obesity, <600 MET-min/week of physical activity (Table 1).

Multivariable logistic regression showed that, overall, the presence of cataract was associated with significantly higher odds for depression (OR = 1.655; 95% CI = 1.295-2.115). In the gender-stratified analyses, cataracts were significantly associated, only in women, with higher odds for depression (OR = 1.762; 95% CI = 1.307-2.374) and for chronic anxiety (OR = 1.519; 95% CI = 1.067-2.163) (Tables 2, 3).

The suitability of the regression models was assessed. The final model for predicting depression was a significant improvement in fit over the null model [χ²₍₁₄₎ = 160.016, p < 0.001], Pearson's chi-square test indicated that the model fitted the data well [χ²₍₃₅₃₎ = 350.802, p = 0.523] and the deviance chi-square indicated a good fit [χ²₍₃₅₃₎ = 378.894, p = 0.164]. The model for predicting chronic anxiety showed a significant improvement in fit over the null model [χ²₍₁₃₎ = 99.045, p < 0.001], Pearson's chi-square test indicated that the model fitted the data well [χ²₍₂₃₅₎ = 235.049, p = 0.487] and the deviance chi-square indicated good fit [χ²₍₂₃₅₎ = 251.149, p = 0.224].

In this large representative sample of Spanish adults with diabetes, we find, for the first time, that women suffering from diabetes and cataracts show significantly higher odds for depression and for chronic anxiety compared to those women who had diabetes but no cataracts.

While the present findings support previous studies showing higher levels of depression and chronic anxiety in people with diabetes (7, 42), it adds to literature by demonstrating that women who have both diabetes and cataract are at much greater risk of mental health complications compared to women with diabetes but no cataract. Also, women who have both diabetes and cataract are at greater risk of mental health complications compared to men with the same conditions, as the association between cataract and mental health was not significant in men with diabetes. The increased risk of depression and chronic anxiety in women with diabetes who have cataracts is of concern as this dual impairment is likely to continue to increase owing to an aging population which leads to both increased prevalence of diabetes and cataracts (43, 44).

There are several plausible mechanisms that may explain the higher risk of depression in people with diabetes who also have cataracts. First, having more than one condition will amplify depression, as multiple conditions require more adjustments for activities of daily living and managing diabetes in the presence of blurred vision (caused by cataracts). Second, managing diabetes and cataracts may need additional medical interventions, and literature suggests that medical intervention is linked to discomfort and uncertainty (45) and is a stressor for depression. Third, if depression is managed through anti-depression medication, this may actually worsen the status-quo as these have been shown to be a risk factor for cataracts (46). Fourth, people with diabetes who also have cataracts experience reduced vision-related changes in quality of life, which might contribute to the development of depression (47).

Possible reasons for cataracts to be significantly associated with higher odds for depression and anxiety in women with diabetes but not in men could be explained by some biological and genetic differences between men and women. Recent evidence suggests that biological factors such variations in ovarian hormone levels and particularly decreases in estrogen may contribute to the increased prevalence of depression and anxiety in women (48). Women with cataracts are more affected than men with regards to the cataract-related medical interventions that may be required (45) and about the vision-related changes in the Quality of Life caused by cataract (47). Previous research suggests that women also have a lower tolerance for stress than men (49). Future studies should explore these reasons in detail.

The large representative sample of the Spanish population and the novel associations investigated are clear strengths of this study. Findings, however, must be interpreted in light of the study limitations. First, the study is cross-sectional in nature thus it is not known whether those with diabetes and anxiety or depression develop cataracts or those with diabetes and cataracts develop anxiety or depression. It is likely bidirectional. A longitudinal study would further explore the identified associations. Second, participants were asked “have you ever been diagnosed with cataracts,” “have you ever been diagnosed with anxiety (or depression),” and “have you ever been diagnosed with diabetes.” It is therefore possible that those participants who reported affirmatively to all questions did not have all conditions at the same time. Also, it is possible that people who responded affirmatively to having cataracts might have had their cataract removed. If that was the case, then we should in fact see higher odds ratios in people who have not had the operation, and it is possible that what we have shown may be underestimate. Also, all questions were self-reported, introducing self-reporting and recall bias into the findings. Finally, there was information about the chronic conditions studied in the present study (diabetes, cataract, depression and chronic anxiety) that were not included in the survey, such as duration of the disease, treatment and type or severity, being recommendable that future studies consider also these aspects.

In conclusion, cataracts are a significant risk factor for depression and chronic anxiety in Spanish women with diabetes, but not in men. It would be important for healthcare practitioners to take this into account, and manage both cataract and diabetes with appropriate and timely interventions to reduce the risk of further mental health complications, especially in women.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethical review and approval was not required for the study on human participants in accordance with the local legislation and institutional requirements. Written informed consent to participate in this study was provided by the participants' legal guardian/next of kin.

All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

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.

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