Single people carry a 42% higher risk than married couples of developing dementia, a meta-analysis by US researchers has found.
The analysis – which covered 15 separate studies comprising 812,000 participants – also found that being widowed increased dementia risk by 20%. Being divorced, however, did not seem to affect the risk at all.
The scientists, led by psychiatrist Andrew Summerlad of University College, London, based their analysis on earlier research that found being married was associated with over all healthier lifestyle behaviours and lower all-cause mortality. They asked whether the benefits also included lower dementia risk.
Combing through the results of studies from Europe, North and South America they found that marriage was linked to a lesser incidence of dementia – a finding that remained robust after corrections for factors such as age, health, economic and educational status.
Dementia risks associated with being single or with widowhood (for males and females) varied according to how the candidate studies had been constructed, but were evident throughout.
Summerlad and his colleagues offer a range of possible explanations to accommodate the findings.
“First, being married may change individuals’ exposure to other protective and risk factors throughout their subsequent lifespan,” they write in the Journal of Neurology, Neurosurgery and Psychiatry.
They note, too, that models of social interaction often differ between married and single people, with the former “building cognitive reserve”. They argue that better outcomes for married people aren’t simply because they enjoy better health, but because “there may a direct cognitive benefit [to] being married”.
The increased dementia risk for single people might also be a function of a wider issue, in which they are more likely to be under-diagnosed for conditions across the board. This possibility was bolstered, the scientists reported, by the fact that the relative risk tended to decrease in more recent studies – indicating more attentive testing by doctors.
In general, single people had higher rates of contributing factors such as reduced physical inactivity, less education, and higher rates of smoking and hypertension. People who lived alone were also less likely to report key symptoms, such as memory loss.
The increased dementia risks arising from widowhood, the team notes, is supported by earlier studies that show bereavement creates a “detrimental effect of stress on hippocampal neurons or cognition”. This could explain why divorce – where the pain of a loved one’s death is absent – was not found to change the risk profile.
Summerlad and colleagues conclude with a call for more research into the relationship between marital status and dementia risk, particularly in the effects of health behaviours and social contact.