Dementia Risk Higher in Spouses of Dementia Patients

By Joyce Frieden, News Editor, MedPage Today
Reviewed by Zalman S. Agus, MD; Emeritus Professor
University of Pennsylvania School of Medicine.

Spouses of dementia patients are six times more likely to develop dementia than spouses of persons without dementia, a study has found.

The fully adjusted hazard ratio for developing dementia after being exposed to a spouse's dementia was 6.0 (95% CI 2.2 to 16.2, P<0.001), according to Maria C. Norton, PhD, of Utah State University in Logan, and colleagues.

In analyses by sex, the effect of exposure to a spouse's dementia was higher for men (HR 11.9, 95% CI 1.7 to 85.5) than women (HR 3.7, 95% CI 5 1.2 to 11.6), the authors reported in the May issue of the Journal of the American Geriatrics Society.

However, "given the overlap in confidence intervals, the difference could be due to chance and needs further study," they added.

The distress of watching a spouse suffer from dementia and the physical and mental burden of providing dementia care are potential causal factors, given the influence of care-giving on risk for depression and mortality, the authors suggested.

"Having a loved one with dementia is stressful regardless of age, but the burden for spouses may be even greater because of close emotional ties to their partner, their own medical comorbidity, greater risk for functional limitations, and greater likelihood of fatigue with physical exertion."

One specific mechanism might be the detrimental effects of chronic stress on the hippocampus, a brain region responsible for memory, they theorized, noting that "there may be a relationship between having a spouse with dementia and adverse cognitive function with stress as the potential mediator."

To see whether older married adults would be at greater risk of dementia after onset of dementia in their spouses, the authors examined existing data from the Cache County (Utah) Study on Memory Health and Aging. This is a population-based epidemiological study of county residents ages 65 and older.

Norton and colleagues identified 1,221 married couples in the database as suitable for the study. Average age of respondents was 75.7 for husbands and 73.1 for wives. The couples were followed for up to 12.6 years, with a median follow-up of 3.3 years. Apolipoprotein E (APOE) genotypes were obtained at baseline.

The study used a multistage protocol for diagnosing dementia. Screening began with an in-person interview, including the modified Mini-Mental State Examination or, for those unable to participate, the Informant Questionnaire on Cognitive Decline in the Elderly.

Participants whose screening scores suggested possible dementia then completed an in-depth clinical assessment.

Specially trained nurses and psychometric technicians administered the clinical assessment, which included a brief physical evaluation, a history of medical and cognitive symptoms, a structured neurological examination, and a one-hour battery of neuropsychological tests.

A geriatric psychiatrist and neuropsychologist, along with the assessment team, reviewed these data and assigned working diagnoses of dementia or other cognitive syndromes based on DSM-III-R criteria.

Of the 2,442 people selected for the dementia study, 253 screened positive for dementia but failed to complete the clinical assessment because they died, refused to continue, or moved out-of-state after the initial screening.

However, some of those respondents had completed a dementia questionnaire after the initial screening, and scores from the questionnaire were used to impute dementia status. For the remaining respondents in this group, the screening data itself was used.

Incident dementia among the 1,221 couples was diagnosed as follows:

•Only in the husband (n=125)
•Only in the wife (n=70)
•In both spouses (n=30)
•In neither spouse (n=996)

Incident dementia was significantly associated with older age, presence of one or more APOE e4 alleles, and having a spouse with dementia.

In 10 couples (0.4%), one spouse resided in a nursing home at baseline. Institutionalization after dementia onset occurred in only 12% of incident cases. All other couples where dementia was present lived together over the entire period of observation.

The authors offered several possible explanations for their finding that spouses of dementia patients were at higher risk of the disease.

One possibility was shared environmental exposures.

Another possibility was socioeconomic status. Although the models used did account for socioeconomic status (SES), "adjustment for SES does not provide a complete control for potential confounders, such as access to medical care, smoking, alcohol consumption, and diet, although the random effects models controlled for shared, unmeasured exposures without any appreciable change in the findings," they noted.

A third mechanism may be homogamy, or positive assortative mating, "to the extent that similarity in proneness to distress or mental illness may influence shared risk for dementia in couples," they wrote.

They concluded that "the relative contribution of each of these potential mechanisms to this overall effect is unknown and needs further study."

Regardless of which mechanisms are creating this effect, "it is imperative that more research be conducted to help protect older adults with spouses who are suffering from dementia from suffering the same fate themselves," the authors wrote.

Study strengths included a large, community-based sample that avoided the selection bias of clinical samples, along with high baseline participation rate, and longitudinal follow-up.