"This research is important because the number of unmarried older adults in the US continues to grow. As people live longer and their marital histories become more complex, marital status is an important but overlooked social risk/protective factor for dementia," said Hui Liu, Professor at Michigan State University.
For the study, published in The Journals of Gerontology, the researchers analysed nationally-representative data from the Health and Retirement Study, from 2000-2014.
The researchers analysed more than 15,000 respondents aged 52 and older, and measured their cognitive function every two years.
They categorised people into four groups divorced or separated, widowed, never married, and co-habiters. Among them, the divorced had the highest risk of dementia.
The researchers also found differing economic resources only partly account for higher dementia risk among divorced, widowed and never-married respondents, but did not account for higher risk in co-habiters.
In addition, health-related factors such as behaviours and chronic conditions slightly influenced risk among the divorced and married, but did not seem to affect others.