July 10, 2009 — Single people have twice the risk of developing dementia and Alzheimer's disease later in life compared with married or cohabitating people, a new study suggests. Reporting online July 2 in BMJ, investigators say there is a substantial and independent association between marital status and cognitive function.
Being widowed or divorced in midlife increased the risk even more, the authors report, to 3 times the incidence of cognitive decline.
The researchers, led by senior investigator Miia Kivipelto, MD, from the Karolinska Institutet, in Stockholm, Sweden, suggest that living in a relationship with a partner might lead to cognitive and social stimulation that has a protective effect against cognitive impairment. "This is consistent with the brain-reserve hypothesis," they note.
But in an accompanying editorial, Catherine Helmer, MD, from the Université Victor Segalen Bordeaux, in France, questions whether marital status protects against dementia or if the effect could be influenced by stressful experiences such as losing a loved one.
Two Times the Risk of Cognitive Decline
"Marital status seems to be only 1 risk factor among others, with a relatively small contribution to the development of dementia," Dr. Helmer argues. "A change in marital status for cognitive reasons is probably rare in late life, but reverse causation cannot be excluded, because of the long prodromal phase of dementia, particularly Alzheimer’s disease."
To deal with the problem of reverse causation, the investigators evaluated marital status more than 20 years before the onset of dementia or cognitive impairment. They also looked at the causes of unmarried status.
Researchers interviewed a random sample of 2000 people who took part in the more-than-20-year-long Cardiovascular Risk Factors, Aging, and Dementia study. Participants came from 2 regions in eastern Finland.
Lead author Krister Håkansson, a research fellow at the Karolinska Institute, and colleagues found that people cohabiting with a partner in midlife (mean age, 50.4 years) were less likely than those who were single, separated, or widowed to show cognitive impairment later in life (age 65 to 79 years).
Those widowed both at midlife and later in life had an odds ratio of 7.67 (95% CI, 1.6 – 40.0) for Alzheimer's disease compared with married or cohabiting people.
Researchers saw the highest increased risk for Alzheimer's disease in carriers of the apolipoprotein E e4 allele who lost their partner before midlife and were still widowed or divorced at follow-up.
"To understand the link between marital status and dementia, future research should focus on 2 points," Dr. Helmer suggests: the stress caused by a separation and the biological consequences of this stress; and the quality of social engagement. "The satisfaction with relationships," she notes, "is probably at least as important as the quantity of social engagement but remains hard to evaluate in epidemiological studies."
The researchers have disclosed no relevant financial relationships.
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