Being married, or ever having been married, comes with a much lower risk of developing dementia compared to being a lifelong bachelor or bachelorette, a new analysis of previous studies suggests.
Researchers found that people who never married were 42 percent more likely than those who were married at midlife to ever be diagnosed with dementia. Being divorced, though, was not tied to higher dementia risk compared with the folks who stayed married.
"Our findings, from large populations across numerous countries and time periods, are the strongest evidence yet that married people are less likely to develop dementia. We can be fairly certain of this considering that we have looked at close to a million people," said lead author Dr. Andrew Sommerlad of University College, London.
"What we can't be certain of in this study is what the explanation for this is," he said in a phone interview.
Sommerlad and his team analyzed 15 studies published up to the end of 2016 that looked at the potential role of marital status on dementia risk. The new analysis included more than 812,000 participants in those studies, half of whom were 65 years of age or older. The studies were done in Europe, North and South America and Asia.
Although one study from Sweden contributed the vast majority of participants, the other studies were also broadly in agreement with the results of that one, the authors note in the Journal of Neurology, Neurosurgery & Psychiatry.
"There's a huge literature showing that marriage is beneficial for health in lots of different ways," said Joan Monin of the Yale School of Public Health in New Haven, Connecticut, who wasn't involved in the study. "Spouses share specific healthy behaviors for wellbeing like engaging in physical activities, watching their diet and limiting substance abuse," she said in a phone interview.
The widowed have a 20 percent increased risk of developing dementia compared with married individuals, Sommerlad noted. He speculates that this may be due to the stress of bereavement, or a longer-term effect.
As for the lack of difference between married people and those who divorced, Sommerlad attributes it to the possibility that a lot of divorced people continue to keep in contact with each other, especially if they have children together.
Social isolation is one of the nine risk factors for dementia identified by the Lancet Commission on Dementia, Prevention, Intervention and Care in July.
Worldwide there are nearly 47 million people living with dementia, or a loss of brain function, including memory, thinking and behavior, according to the World Health Organization. Alzheimer's disease is the most common cause of dementia.
Sommerlad emphasized that no cause-and-effect conclusions can be drawn from his team's analysis because it's not known what underpins the results. Another limitation is that the included studies lacked information about the duration of widowhood and divorce as well as the nature of the marriages.
"The institution of marriage is undergoing rapid changes with the acceptance of same-sex marriages and alternatives to marriage, such as cohabitation," Dr. Christopher Chen of the Yong Loo Lin School of Medicine at the National University of Singapore and a co-author write in an editorial accompanying the study.
"There have been large changes in society so we need to be aware that the conclusions may not be as relevant," Chen told Reuters Health by email.