Compared to married people, single people for life are 42% more likely to develop dementia, according to the study of more than 800,000 people. Meanwhile, those who have lost a spouse are 20% more likely to develop dementia, according to the study.
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Even when researchers explored different "subtypes" of dementia – from Alzheimer's disease to vascular dementia (a type caused by a stroke) – their results have not changed, says study author Andrew Sommerlad, researcher in clinical training and researcher in brain science at University College London
. This is not clear, but Sommerlad says that there are some theories.
Previous research has shown that married people – especially married men – tend to live healthier lives than single men. Exercise, in particular, can reduce your risk of dementia by up to 50%. So, if being married leads to people eating better, this could explain the results of the study.
Sommerlad says that married people also have more "social stimulation" than singles, which could bring anti-dementia benefits. A 2015 study revealed a lack of social interaction is associated with a higher risk of dementia.
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Spending time talking and socializing with other people is cognitively demanding, and could stimulate the brain in ways that to prevent dementia. Sommerlad and his co-authors of the study say that socializing with others is also a great way to relieve stress, which could also help explain the links of activity to reduce dementia rates  MORE: Your Young Brain
What about the divorced?
Although some previous research has linked stressful midlife events – including divorce – to a high risk of dementia, this study did not reveal any risk. Sommerlad and his colleagues say that divorce, while undoubtedly stressful, is not as traumatic as the loss of a spouse and that it is not likely to cause an increased risk of dementia. (Difficult in your marriage? Try these 15 tips that divorce lawyers use to strengthen their relationships.)
How can you avoid dementia?
Whether you're married or single, Sommerlad says, "What's good for the heart, that's regular exercise, first and foremost, is probably your best defense against dementia (these 10 ways to prevent heart disease can also be protective.)
He says spending time socializing, eating healthy, and getting prompt treatment for medical problems are more convincing ways of getting healthy. make sure your head (and your heart) stays healthy.
Finally, "maintaining brain stimulation" seems to be an effective way to prevent dementia, he says. suggests regular meditation is one way to keep your mind sharp. A form of brain training on computer can also protect your mind from the ravages of dementia, recent research shows.