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Dementia and marital status at midlife and late life - Editorials
  Published 2 July 2009, doi:10.1136/bmj.b1690 BMJ 2009;339:b1690
Risk is increased in people who are unmarried, especially if they are widowed
Marital status late in life has been related to the risk of dementia or cognitive decline in the next 3-10 years. People who were classified as unmarried,1 single,2 3 and single living alone4 are at increased risk of dementia or cognitive decline. This association was true even after adjustment for activities, social engagement, and living conditions and was independent of other risk factors for dementia.
Marital status seems to be only one risk factor among others, with a relatively small contribution to the development of dementia (relative risk 1.5-2.5). 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.5
In the linked study (doi:10.1136/bmj.b2462, Hakansson and colleagues evaluated marital status more than 20 years before the onset of dementia or cognitive impairment and thus dealt with the problem of reverse causation.6 Moreover, causes of unmarried status were explored. They followed 1449 people in Finland aged 65-79 years for an average of 21 years and found a twofold increase in the risk of both cognitive impairment and dementia about 21 years later for unmarried people compared with those who were married. People who had been widowed were at particularly increased risk, with about a threefold increased risk. In addition, when considering the evolution of marital status over the 21 year period, people who cohabited in midlife but not late in life tended to be at increased risk, although results were only borderline significant. People who did not cohabit in both midlife and late life were at the highest risk, with risks especially high again for those who were widowed.
One explanation to the possible protective effect of cohabitation on cognitive impairment and dementia is the reinforcement of cognitive reserve.7 Indeed, increased stimulation throughout life among cohabitants could allow better recruitment of the neuronal network that protects against or delays the onset of dementia. This effect could be lifelong.
The theory of cognitive reserve could explain current and previous results that link both midlife and late life marital status with dementia. However, confounding factors like social activities and involvement in life, as well as risk behaviours, need to be considered. The only previous study that evaluated midlife marital status in men failed to find an association between a midlife social engagement index, that included marital status, and subsequent risk of dementia; only the late life social engagement index was associated.8 Unfortunately, although Hakansson and colleagues had data on health factors and physical activities, they lacked data on social engagement in midlife.6
Hakansson and colleagues put forward an alternative explanation on the basis of a higher incidence of dementia and cognitive impairment in people who were widowed during midlife.6 Rather than marital status protecting against dementia, it could have its effect through the deleterious effects of stressful experiences such as widowhood, which could be linked with immunological dysfunction. However, the results for people who were widowed or divorced after midlife had only borderline significance, and previous studies failed to identify being widowed as a particular risk.
One possibility is that the age and conditions of widowhood are crucial factors. Being widowed late in life, as were most of the people in previous studies, is perhaps less stressful-especially as the person is widowed for a shorter duration-and might thus not be a risk factor. Nevertheless, the hypothesis of a deleterious biological effect of widowhood remains to be proved, as does the possibility of genetic vulnerability as a link between widowhood and dementia. This genetic hypothesis has been formulated on the basis of exploratory results showing a higher incidence of cognitive impairment for widowed or divorced apoE4 carriers than for non-carriers. However, caution is needed here. Indeed, in epidemiological studies, comparisons of risks between subgroups can rarely be interpreted directly, particularly when confidence intervals are large, and they should be validated by testing an interaction term.
Beyond dealing with reverse causation, the evaluation of marital status in midlife strengthens the hypothesis that the development of cognitive impairment and dementia is a long process that is affected by various factors throughout life. To understand the link between marital status and dementia, future research should focus on two points. Firstly, the accurate assessment of stress caused by a separation and the biological consequences of this stress; secondly, the quality of social engagement4-that is, satisfaction with relationships-which is probably at least as important as the quantity of social engagement but remains hard to evaluate in epidemiological studies.
A potential application of the findings involves collecting and using data about patients' marital status, which is easy to do in primary care. Unmarried, especially widowed, people could then be targeted for preventive strategies that encourage them to increase their social engagement by taking part in cultural, social, and sporting activities.
Cite this as: BMJ 2009;339:b1690
Catherine Helmer, researcher, epidemiologist
1 INSERM, U 897; Universite Victor Segalen Bordeaux 2, 33 076 Bordeaux Cedex, France Research, doi:10.1136/bmj.b2462
Competing interests: None declared.
Provenance and peer review: Commissioned; not externally peer reviewed.
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