Krister Hakansson of Karolinska Institutet in Stockholm, Sweden and Vaxjo University, School of Social Sciences in Vaxjo, Sweden, examined 1,449 individuals from the Finnish Cardiovascular Risk Factors, Aging, and Dementia study in midlife and then again in 1998 -- an average of 21 years later.

At re-examination, 139 people were diagnosed with some form of cognitive impairment: 82 with mild cognitive impairment and 48 with Alzheimer's. Those living with a partner in midlife were significantly less likely to show cognitive impairment compared to all other categories -- single, separated, divorced or widowed. Those in the study who were married or lived with a significant other in midlife had a 50-percent lower risk of having dementia in late life compared to those who lived alone, even after adjustments for education, weight, cholesterol, blood pressure, occupation, physical activity, smoking habits, depression, genes and gender.

The all-life singles had a doubled risk, whereas the ones who stayed divorced from midlife onward had a tripled risk. Those widowed before midlife and who remained living along had the highest risk.

The research was presented at the Alzheimer's Association International Conference on Alzheimer's Disease in Chicago.