Among older adults, a significant decrease in body mass index (BMI) occurs approximately 7 years prior to receiving a diagnosis of mild cognitive impairment (MCI), according to study findings published in JAMA Psychiatry.
Researchers sourced data from the Rush Memory and Aging Project (MAP), which was conducted at Rush University Medical Center in the United States between 1997 and 2020. Adults (N=1390) aged 60 to 90 years who had normal cognitive function were evaluated for longitudinal changes in BMI and cognitive status.
Study participants’ mean age was 78.4 (SD, 6.5) years at baseline, 76.5% were women, and 85.6% were White.
During a median follow-up period of 6 years, 39.5% of individuals were diagnosed with MCI, among whom 23.7% progressed to dementia. The individuals who developed MCI were younger (mean, 79.6 vs 76.9 years), more were men (23.2% vs 21.1%), fewer were former or current smokers (36.9% vs 41.5%), they consumed less alcohol (median, 0 vs 1.1 g/d), and had greater physical activity (median, 2.2 vs 1.9 h/wk) compared with those who did not develop MCI, respectively.
Stratified by MCI status and counting backwards, the MCI-free and incident MCI cohorts did not differ for BMI (mean difference [MD], 1.42; 95% CI, -1.37 to 4.22 kg/m2; P =.31) 18 years prior to MCI diagnosis. The MCI cohort had a significantly lower BMI than the MCI-free cohort (MD, -0.96; 95% CI, -1.85 to -0.07 kg/m2; P =.03) starting at 7 years prior to MCI diagnosis. This significant difference continued every year until the year they were diagnosed with MCI (MD, -0.92; 95% CI, -1.82 to -0.02 kg/m2; P =.04) compared with the non-MCI group.
Among the MCI cohort, BMI continued to decline among individuals who did (β, -0.20) and did not (β, -0.17) eventually develop dementia during the 10 years between MCI and dementia diagnoses. Overall, no group differences in BMI were observed (β, -0.04; 95% CI, -0.23 to 0.14; P =.63).
A subset of participants (n=520) underwent brain autopsy following death. The patients who exhibited higher burden for brain pathology had a significantly faster decline in BMI (β, -0.14; P =.02). A similar trend was observed for patients with cerebral vascular disease pathology (β, 0.20; P =.03).
The major limitation of this study was that these volunteers had a high level of education and performed well on cognitive tests at baseline, which may limit the generalizability of these findings.
Study authors concluded, “This cohort study provides evidence on the long-term BMI decline before the development of MCI and the progression of MCI to dementia. Compared with cognitively intact individuals, those who develop MCI may experience a significant associated BMI decline earlier and have a lower BMI starting from approximately 7 years before MCI diagnosis. BMI continues to decline after MCI diagnosis at the same pace in people who develop dementia and those who do not.”
Guo J, Wang J, Dove A, et al. Body mass index trajectories preceding incident mild cognitive impairment and dementia. JAMA Psychiatry. Published online October 26, 2022. doi:10.1001/jamapsychiatry.2022.3446