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BMC Medicine
Published in: BMC Medicine 1/2020

01-12-2020 | Obesity | Research article

Age-dependent effects of body mass index across the adult life span on the risk of dementia: a cohort study with a genetic approach

Authors: Ida K. Karlsson, Kelli Lehto, Margaret Gatz, Chandra A. Reynolds, Anna K. Dahl Aslan

Published in: BMC Medicine | Issue 1/2020

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Abstract

Background

While a high body mass index (BMI) in midlife is associated with higher risk of dementia, high BMI in late-life may be associated with lower risk. This study combined genetic designs with longitudinal data to achieve a better understanding of this paradox.

Methods

We used longitudinal data from 22,156 individuals in the Swedish Twin Registry (STR) and 25,698 from the Health and Retirement Study (HRS). The STR sample had information about BMI from early adulthood through late-life, and the HRS sample from age 50 through late-life. Survival analysis was applied to investigate age-specific associations between BMI and dementia risk. To examine if the associations are influenced by genetic susceptibility to higher BMI, an interaction between BMI and a polygenic score for BMI (PGSBMI) was included in the models and results stratified into those with genetic predisposition to low, medium, and higher BMI. In the STR, co-twin control models were applied to adjust for familial factors beyond those captured by the PGSBMI.

Results

At age 35–49, 5 units higher BMI was associated with 15% (95% CI 7–24%) higher risk of dementia in the STR. There was a significant interaction (p = 0.04) between BMI and the PGSBMI, and the association present only among those with genetic predisposition to low BMI (HR 1.38, 95% CI 1.08–1.78). Co-twin control analyses indicated genetic influences. After age 80, 5 units higher BMI was associated with 10–11% lower risk of dementia in both samples. There was a significant interaction between late-life BMI and the PGSBMI in the STR (p = 0.01), but not the HRS, with the inverse association present only among those with a high PGSBMI (HR 0.70, 95% CI 0.52–0.94). No genetic influences were evident from co-twin control models of late-life BMI.

Conclusions

Not only does the association between BMI and dementia differ depending on age at BMI measurement, but also the effect of genetic influences. In STR, the associations were only present among those with a BMI in opposite direction of their genetic predisposition, indicating that the association between BMI and dementia across the life course might be driven by environmental factors and hence likely modifiable.
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Metadata
Title
Age-dependent effects of body mass index across the adult life span on the risk of dementia: a cohort study with a genetic approach
Authors
Ida K. Karlsson
Kelli Lehto
Margaret Gatz
Chandra A. Reynolds
Anna K. Dahl Aslan
Publication date
01-12-2020
Publisher
BioMed Central
Published in
BMC Medicine / Issue 1/2020
Electronic ISSN: 1741-7015
DOI
https://doi.org/10.1186/s12916-020-01600-2

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