Older adults were more likely to have cognitive disorders—defined as dementia or mild cognitive impairment—if their spouse also had cognitive disorders, a prospective cohort study showed.
Cognitive disorders in study participants nearly doubled the risk of cognitive disorders in their spouses (odds ratio [OR] 1.74, 95% CI 1.12-2.69, P=0.01), reported Ki Woong Kim, MD, PhD, of Seoul National University in Korea, and co-authors.
Factors shared by couples mediated about three-quarters of that risk, they wrote in JAMA Network Open.
“Our objective was to identify the risk factors shared within couples and examine their mediating roles in the shared risk of cognitive disorders and cognitive functions within couples in a population based, couple cohort study,” Kim and colleagues wrote. “These findings suggest that the risk factors shared within couples may mediate approximately three-quarters of the spousal risk of cognitive disorders.”
“This study demonstrated that participants’ cognitive disorders were associated with spouses’ declines in cognitive function and risks of cognitive disorders, and that this association was mediated by factors including physical inactivity and a history of head injury, which were shared within couples,” the researchers added. “Identification of and intervention in the shared risk factors of dementia within couples may reduce the risk of cognitive disorders in the spouses of people with dementia.”
Participants were from the Korean Longitudinal Study on Cognitive Aging and Dementia (KLOSCAD), which began in November 2010. Participants were followed every two years through December 2020 for incident dementia or mild cognitive impairment. The cohort included 784 older adults (307 women, 477 men) with a mean age of 74.8. All participants had heterosexual spouses (477 women, 307 men) with a mean age of 73.6, who were identified as a separate cohort (KLOSCAD-S) during the fourth follow-up assessment.
Among the 784 KLOSCAD participants, 121 had cognitive disorders. Cognitive disorders were more prevalent in the group of spouses whose partner in the KLOSCAD cohort was cognitively impaired (38.8% versus 22.6%, P<0.001).
Among four factors (physical inactivity, exposure to smoking, history of head injury, and major depressive disorder) that were concordant within couples, physical inactivity, history of head injury, and major depressive disorder were independently associated with the risk of cognitive disorders in spouses.
Structural equation modeling showed that history of head injury (β=0.50, 95% CI 0.09-0.90, P=0.02) and age (β=2.57, 95% CI 1.37-3.76, P<0.001) mediated the association between cognitive disorder in KLOSCAD participants and their spouses’ risk of cognitive disorder.
Physical inactivity mediated the association through major depressive disorder (β=0.33, 95% CI 0.09-0.57, P=0.006 for physical inactivity; β=0.28, 95% CI 0.13-0.44, P<0.001 for major depressive disorder).
In an accompanying editorial, Peter Vitaliano, PhD, of the University of Washington in Seattle, wrote that the study “makes a major contribution to knowledge about the joint prevalence and risks of cognitive disorders in married couples and the work highlights many areas in which to extend this work as it relates to previous research.”
Vitaliano suggested three relevant areas for further study: assortative mating, dyadic lifestyles, and spouse caregiving.
“Research on assortative mating examines traits and states that occur before mating and that influence both the choice of one’s mate and one’s future health,” he wrote. Prior research has considered associations of assortative mating with genetic profiles, education, and health behaviors, Vitaliano observed.
The dyad itself might provide insight, the editorialist added. “The study’s focus was on similarities within couples, but one might also gain insight into this disease’s causes by examining the patterns of differences within couples,” he wrote.
Caregiver chronic stress, previously associated with worse physiological parameters in a 2003 meta-analysis and the possibility that declines in cognitive function might be partially due to metabolic dysregulation, also are an important area for future research, he noted.
“According to the 2020 report of the Lancet Commission, 40% of dementia cases can be prevented or delayed by modification of 12 risk factors,” Kim and colleagues wrote. “Most of these factors, such as educational attainment, cardiometabolic disease, lifestyle factors, and depression, tend to be highly shared within couples with or without dementia.”
“Although it is not possible to infer a causal relationship, our results suggest that spousal cognitive disorders could lead to a shared sedentary lifestyle within couples, which may be associated with the risk of cognitive disorders through association with depression,” the researchers added. “Therefore, encouraging physical activity in spouses of cognitively impaired patients may be a meaningful intervention to prevent cognitive disorders.”
Limitations include the study’s cross-sectional design with its possibility of reverse causation and inability to make causal conclusions. The study also could not analyze dementia and mild cognitive impairment separately due to small sample size.
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Older adults were more likely to have cognitive disorders if their spouse also had cognitive disorders, a prospective cohort study showed.
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Factors shared by couples—including physical inactivity and history of head injury—mediated about three-quarters of that risk.
Paul Smyth, MD, Contributing Writer, BreakingMED™
The study was supported by a grant from the RKCDC.
Kim reported receiving support from the RKCDC.
Vitaliano had no disclosures.
Cat ID: 130
Topic ID: 82,130,282,404,494,730,130,361,255,925
