Dementia is a major cause of disability and death among people over the age of 65 globally (Li et al., 2015; GBD, 2019). Currently, more than 50 million people are living with dementia worldwide and this number is expected to exceed 150 million by 2050 (GBD, 2022), imposing a heavy burden on society and families. However, very limited treatment options are available for dementia, highlighting the importance of identifying modifiable risk factors and protective factors to reduce the incidence of this disease.

Hypertension is now recognized as one of the most common modifiable risk factors for dementia. Strong evidence suggests that the risk of all-cause dementia is increased by about 60% in middle-aged hypertension (Livingston et al., 2020). However, research on elderly populations yielded controversial results regarding the relationship between systolic blood pressure (SBP), diastolic blood pressure (DBP) and dementia. Some studies reported no association (Hebert et al., 2004; Gottesman et al., 2014; van Middelaar et al., 2018), while others found U-shaped (Lv et al., 2017) or Hockey-stick-shaped associations (Yuan et al., 2019). These inconsistent findings may be due to various factors influencing the relationship between blood pressure and dementia, such as age, sex, genetics, regional lifestyle and antihypertensive drugs (Hanon et al., 2004; Kern et al., 2017; Levine et al., 2022; Omboni et al., 2023).

As people age, SBP gradually increases and DBP gradually decreases due to decreased elastic function of large arteries and atherosclerosis (Omboni et al., 2023). Additionally, low DBP can reduce brain perfusion, increasing the risk of dementia (Lee et al., 2020; Suri et al., 2020). A prospective cohort study reported a decline in DBP in the years preceding dementia onset (Skoog et al., 1996).

Non-invasive arterial stiffness measurements, such as pulse pressure (PP) and mean arterial pressure (MAP), have long been used to assess the risk of cardiovascular events in elderly individuals (Assmann et al., 2005; Zheng et al., 2008; Hadaegh et al., 2012). Recent studies have shown that high PP increases the risk of dementia (Jung et al., 2020; Li et al., 2022), although not all studies agree (Lv et al., 2017). Other studies have suggested that MAP may be a better blood pressure predictor of dementia (Lv et al., 2017; Santillo et al., 2024). Nonetheless, further studies are required to clarify their relationship with dementia.

Following research on blood pressure, a new indicator called the blood pressure index (BPI) was developed (Ates et al., 2017a,b). One study showed that older adults with a high BPI were more likely to develop cognitive decline (Naharci and Katipoglu, 2021). The primary mechanism may be a decrease in cerebral blood flow due to a decrease in cardiac ejection volume, leading to an increased risk of cognitive impairment (Kresge et al., 2020). However, there is a relatively limited amount of data regarding the relationship between BPI and dementia among Chinese community-dwelling older adults.

In summary, this study aimed to investigate the relationship between various blood pressure indicators (SBP, DBP, MAP, PP and BPI) and dementia in older adults aged 65 and above.

In a cross-sectional study of 3,599 Chinese community-dwelling older adults aged 65 years and older, this study revealed a U-shaped relationship between DBP and dementia, which was particularly significant for male and older adults aged 70 years and older. In addition, there was a linear relationship between BPI and dementia.

The effect of blood pressure on dementia in older adults is controversial (Hebert et al., 2004; Lv et al., 2017; Ou et al., 2020; Badji et al., 2021) and most studies have focused primarily on SBP, with less attention to DBP. The present study revealed a U-shaped correlation between DBP and dementia, consistent with several previous studies (Lee et al., 2022; van Dalen et al., 2022). In this study, with dementia risk being lowest at 85 mmHg DBP, the findings align with those of Lv et al. (2017). Moreover, the optimal range for DBP control in older adults is 80–99 mmHg, which is similar to the conclusion of 90–100 mmHg from a prospective systematic review (Ou et al., 2020). However, the study by Kumar B. Rajan et al. reported that each 5 mmHg increase in DBP above 76 mmHg was linked to a 57% greater risk of developing Alzheimer’s disease (AD) (Rajan et al., 2018). Specific optimal protective DBP values require further longitudinal studies. Nonetheless, it is undeniable that DBP plays an important role in controlling blood pressure in elderly people, and lower blood pressure does not necessarily equate to improved health. The U-shaped relationship between DBP and dementia identified in this study was more pronounced in adults aged 70 years and older. A prospective study in the Bronx Ageing Study reached a similar conclusion, suggesting that low DBP was associated with the risk of dementia in people aged 75 and older (Verghese et al., 2003). Therefore, in older adults (>70 years) with isolated systolic hypertension who already have a low DBP, antihypertensive therapy may be administered with more caution (Angeli et al., 2020; Rivasi et al., 2023).

Our findings also revealed a sex difference in the U-shaped relationship between DBP and dementia, showing a significant association only in males. This finding is in agreement with the conclusions of several previous studies (Gao et al., 2021; Gong et al., 2021). Possible reasons for this result are the differences in sex chromosomes, sex hormones, environmental factors, and lifestyle habits between males and females, which contribute to differences in the physiological and pathological processes that regulate blood pressure in males and females (Gerdts et al., 2022). Little attention has been given to sex differences in the relationship between DPB and dementia in previous studies. Therefore, further investigations are required to confirm these possible sex differences and to identify the underlying mechanisms.

BPI is a new index obtained by dividing SBP by DBP, which is mainly used to reflect heart failure and right heart insufficiency in clinical practice (Ates et al., 2017a,b). Less attention has been paid to the relationship between this parameter and dementia among Chinese community-dwelling older adults. In the present study, BPI was found to be associated with dementia in older adults. The main mechanism may be attributed to reduced cerebral blood flow due to decreased cardiac ejection, causing an increased risk of dementia (Kresge et al., 2020). In addition, a high BPI indicates a severe degree of arterial stiffness and atherosclerosis, thus increasing the risk of dementia (van Popele et al., 2001). Previous studies have reported that dementia and its two main subtypes, AD and vascular dementia, are both associated with atherosclerosis, with the etiology of AD involving the interaction between ApoE and atherosclerosis (Hofman et al., 1997; van Oijen et al., 2007). Thus, from a biological point of view, SBP increases with age, while DBP decreases, resulting in an increase in BPI, which can be linked to dementia in later life through pathologic changes (van Popele et al., 2001; Kresge et al., 2020; Omboni et al., 2023). In addition, the relationship between BPI and dementia found in this study may help to understand the association between cardiovascular risk factors and dementia in later life.

Some studies have shown that MAP is associated with an increased risk of dementia (Lv et al., 2017; Santillo et al., 2024). However, a study by Cui et al. with a 15-year follow-up revealed that MAP was not associated with an increased risk of dementia (Cui et al., 2018). In the present study, a U-shaped relationship was found between MAP and dementia in GAMs and segmented regression model; nonetheless, additional logistic regressions did not support this. In addition, a cohort study found that older adults with higher levels of SBP had a lower risk of dementia and a more pronounced U-shaped relationship was observed between SBP and the risk of dementia in older adults over the age of 75 (van Dalen et al., 2022). Moreover, high PP was found to increase the risk of dementia (Jung et al., 2020; Li et al., 2022). However, in our study, a nonlinear trend was found between SBP and PP and dementia, although the findings were not statistically significant. These inconsistencies may result from different study designs, assessment methods, sample sizes, adjustments for potential confounders, and participant characteristics such as age, sex, and ethnicity (Hanon et al., 2004; Levine et al., 2022; Omboni et al., 2023). Therefore, further research is still required.

At present, the mechanisms underlying dementia due to hypertension or hypotension are incompletely understood and may include the following. First, chronic hypertension can cause atherosclerosis, which leads to vascular remodeling, small vessel occlusion and microvascular damage, resulting in white matter lesions, perivascular gap enlargement, cerebral microhemorrhage and lacunar cerebral infarction (Connelly et al., 2005; Santisteban et al., 2023). Second, hypertension impairs the ability of vascular endothelial cells to regulate cerebral blood flow, with sudden falls in blood pressure resulting in insufficient cerebral perfusion (Iadecola and Gottesman, 2019); in addition, hypertension damages vascular endothelial cells, which leads to blood–brain barrier dysfunction under the combined effect of perivascular macrophages (Santisteban et al., 2020). Furthermore, high blood pressure can affect neurodegenerative disease by impairing vascular integrity, which can result in cerebral amyloid angiopathy, reduced brain clearance of Aβ (Shah et al., 2012) and increased levels of phosphorylated tau protein (Hu et al., 2022). Finally, hypertension can cause abnormalities in the renin-angiotensin-aldosterone system, leading to dementia (Hajjar et al., 2015).

The mechanisms of hypotension may involve inadequate cerebral perfusion, impaired nutrient delivery, impaired waste removal (Suri et al., 2020), and slowed circulation. Distal microvascular ischemia may further lead to neural tissue damage and increase the risk of dementia (Lee et al., 2020). Additionally, the interaction between the APOEε4 allele and low DBP can further elevate the risk of developing AD (Qiu et al., 2003). In late life, low DBP may result in insufficient cerebral perfusion, leading to a chronic hypoperfusion state. This condition may induce or exacerbate abnormal tau protein phosphorylation. Persistent hypoperfusion can cause inadequate oxygen and nutrient supply to brain tissue, promoting neuroinflammation and oxidative stress. These processes may further lead to the abnormal accumulation of tau protein and the formation of neurofibrillary tangles, impairing neuronal function and synaptic connectivity, ultimately leading to the development of dementia (Hu et al., 2022). Furthermore, low DBP often indicates arterial stiffness and loss of elasticity, which are typically manifestations of atherosclerosis. Vascular stiffness caused by atherosclerosis may restrict blood flow to the brain, particularly during diastole when the heart is at rest, limiting the brain’s ability to receive blood through hardened arteries. This reduction in blood flow may lead to chronic cerebral ischemia, especially in vulnerable regions of the brain, such as those involved in memory and cognitive function. These regions, when subjected to prolonged hypoxia and nutrient deprivation, may experience progressive neuronal loss, ultimately leading to the development of dementia (Bots et al., 1996).

The strengths of this study are as follows. First, a large-scale survey of Chinese community members aged 65 years or older was performed. The nonlinear relationship between various blood pressure indicators and dementia was assessed, with a focus on DBP and the new index of blood pressure, BPI. Finally, differences in sex and age were explored.

Nevertheless, the limitations of the present study should be acknowledged. First, since the study was cross-sectional, a causal link between DBP and dementia could not be established. Second, in the blood pressure measurements, 24-h ambulatory blood pressure monitoring was not performed and possible daily changes (circadian rhythms, general physiologic variability, etc) could not be examined. Third, even after adjusting for possible confounders, other factors, such as the APOE-epsilon4 allele, psychological stress, diet and other changes may impact the results. Finally, the participants included in this study were all elderly people in the Tianjin community, so caution is needed when generalizing the results to the entire elderly population.

The present study demonstrated a U-shaped association between DBP and dementia in older adults, particularly pronounced in males and those aged 70 and above. Additionally, a linear association was observed between BPI and dementia in this population. These findings suggest that DBP and BPI are critical factors to consider when counseling older adults on blood pressure management, as they may play a key role in preventing or delaying the onset of dementia. Future prospective cohort studies are needed to confirm these associations.