Body mass index and risk of dementia: Analysis of individual‐level data from 1.3 million individuals

Abstract

Abstract Introduction Higher midlife body mass index (BMI) is suggested to increase the risk of dementia, but weight loss during the preclinical dementia phase may mask such effects. Methods We examined this hypothesis in 1,349,857 dementia‐free participants from 39 cohort studies. BMI was assessed at baseline. Dementia was ascertained at follow‐up using linkage to electronic health records (N = 6894). We assumed BMI is little affected by preclinical dementia when assessed decades before dementia onset and much affected when assessed nearer diagnosis. Results Hazard ratios per 5‐kg/m 2 increase in BMI for dementia were 0.71 (95% confidence interval = 0.66–0.77), 0.94 (0.89–0.99), and 1.16 (1.05–1.27) when BMI was assessed 10 years, 10‐20 years, and >20 years before dementia diagnosis. Conclusions The association between BMI and dementia is likely to be attributable to two different processes: a harmful effect of higher BMI, which is observable in long follow‐up, and a reverse‐causation effect that makes a higher BMI to appear protective when the follow‐up is short.

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Affiliated Institutions

• Inserm FR
• Turku University Hospital FI
• Institute for Molecular Medicine Finland FI
• Alzheimer Scotland GB
• Umeå University SE
• Centre de recherche en Epidémiologie et Santé des Populations FR
• University College London GB
• Finnish Institute of Occupational Health FI
• Finnish Institute for Health and Welfare FI
• Mid Sweden University SE
• University of Helsinki FI
• University of Skövde SE
• Uppsala University SE
• Stockholm County Council SE
• Folkhälsans Forskningscentrum FI
• University of Turku FI
• Stockholm University SE
• Karolinska Institutet SE
• University of Edinburgh GB
• University of Bristol GB

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