In the current study, we demonstrated that non-married status was significant associated with the lower MMSE score and lower MMSE subscore in five major cognitive domains. Moreover, sex was significant effect modifier: non-married people have lower MMSE scores in old men but not in women.
Previous studies have shown that married people are in better health than non-married people, which means they also tend to live longer [7, 10]. Being single or long-term in a bad marriage has many negative consequences, including mental and physical harm, such as depression , suicide , high blood pressure , and the risk of cardiovascular disease and all-cause mortality . There have been some studies on the relationship between marital status and cognitive impairment in the past. Similar to our research, some of these studies have shown that widowed may be a social risk factor for cognitive impairment [8, 9, 26], but not all studies [27, 28]. Research evidence from the United States suggests that widowhood may be a risk factor for cognitive decline, and the cognitive decline of widowed elderly people will accelerate over time [8, 9]. A longitudinal study from South Korea did not come to a completely consistent conclusion. They believed that widowhood increased the risk of cognitive decline regardless of the length of widowhood . The following mechanism could possibly account for the association. Having a spouse usually means that they can get more care in their daily life. Spouses are often an important reason why people can get more understanding and support and participate in more social activities in daily life to increase their cognitive reserve and reduce the risk of dementia, which enhances the ability to deal with neuropathic damage [29, 30]. Living alone and widowhood have been demonstrated to affect health and increase stress, both of which may increase the risk of disease and be associated with cognitive function decline [31, 32]. It is reported that psychological stress activates the hypothalamic– pituitary–adrenal axis activity and increases the levels of glucocorticoid hormones, cause damage to the hippocampal structure and function , affect learning and memory process , increase the deposition in the brain of β-amyloid peptid and τ-protein  and increase the incidence of cardiovascular disease  and hypertension . All of these factors are associated with dementia . In a society where marriage and childbirth are expectations, people who have never married are a very vulnerable group psychologically , which may be one of the reasons why they become the group with the lowest MMSE score. Nevertheless, some longitudinal studies have come to different conclusions that widowhood does not lead to the decline of cognitive ability [27, 28]. The reasons for this different conclusion are still unclear.
Recently, a cross-sectional study involving 1,376 participants in China showed that single men had more severe cognitive impairment than married people, while no similar results were observed in single women . Our results further confirm that gender may be a potential regulatory factor between marital status and cognitive function. Generally speaking, women are more sociable and take better care of themselves when they are alone. What’s more, women tend to take more responsibility for taking care of their spouses in the family, which also means that men will get more health benefits in marriage than women . A study from the United States provided a different view. They did not find gender differences in the relationship between marital status and cognitive impairment . Cultural differences may be the reason for this different result. In China, due to the influence of traditional ideas, divorce is considered a disgraceful thing, especially for women. Therefore, women usually choose to swallow their anger even in the face of marital dissatisfaction. This also means that they may benefit less from a marriage. In the west, men and women are more equal in marriage, which makes their benefits in a marriage closer.
One study related to cognitive function suggests that education is an important protective factor for cognitive decline in later life . Higher levels of education may increase the ability to recover from neurological effects, meaning that people with higher levels of education may need to endure greater impairments to exhibit corresponding cognitive deficits . This may be one reason why male patients with illiterate and primary school education have lower score of MMSE than middle school and above in our study.
Two new insights were provided in our research. First of all, this is the only study in hypertensive patients to investigate the correlation between different marital status and cognitive function. The fact is, the global prevalence of hypertension is very high. In 2010, a total of 1.39 billion people worldwide suffer from hypertension . Hypertension has emerged as a leading cause of cognitive impairment [14, 15], it is necessary for us to increase our attention to this special population. Second, our study focuses on the adults throughout a broad age range and demonstrate that there was a stronger link between cognitive decline and marital status in older men instead of solely focusing on elderly population like Previous studies. These findings will help health policy makers and practitioners identify subgroups that need more attention and to design more effective intervention strategies to reduce the risk of dementia.
We made some efforts to make our research conclusions more convincing. In the subgroup analysis, we observed that MMSE scores were worse in males than in females. For better clarity observation the differences by sex, we re-divide the study population by gender and finally came to this conclusion: Compared with married, non-married people has been associated with greater cognitive impairment in Chinese hypertensive men, especially among older men, but not women. In addition, We use some blood biochemical indicators as confounding factors, which are rarely considered in previous studies. In order to make our research conclusions more representative, our research population comes from various places in Jiangxi Province, and we believe that our research population can represent the Chinese population.
Several potential limitations of our study should be noted. First, as a cross-sectional design, our analysis focused on recording and finding general associations rather than determining causality. we cannot draw any causal relationship between different marital status and cognitive function from this data. Second, we have not recorded the quality of people's marriage and the specific time of the death of their spouse, which may affect people's physical and mental health. Third, when we collect the marital status of the surveyed population, we only focus on their current marital status, without recording their previous marital status. That is to say, we don’t know whether the currently married population has divorced before. In addition, we do not know whether cohabiting partners exist in the people who have never been married at present recorded in our study. These may be Interference to our research conclusions to a certain extent. Fourth, the Chinese version of MMSE test was used in our study can only make a rough assessment of cognitive function . Thus, this tool may not be able to detect subtle changes in cognitive function.