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

• Published in: Alzheimer's & dementia Vol. 14; no. 5; pp. 601 - 609
• Main Authors: Kivimäki, Mika, Luukkonen, Ritva, Batty, G. David, Ferrie, Jane E., Pentti, Jaana, Nyberg, Solja T., Shipley, Martin J., Alfredsson, Lars, Fransson, Eleonor I., Goldberg, Marcel, Knutsson, Anders, Koskenvuo, Markku, Kuosma, Eeva, Nordin, Maria, Suominen, Sakari B., Theorell, Töres, Vuoksimaa, Eero, Westerholm, Peter, Westerlund, Hugo, Zins, Marie, Kivipelto, Miia, Vahtera, Jussi, Kaprio, Jaakko, Singh-Manoux, Archana, Jokela, Markus
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2018; Elsevier, Inc
• Subjects: Aged; Bias; Body Mass Index; Cohort Studies; Cohort study; Data Interpretation, Statistical; Dementia; Dementia - etiology; Female; Global Health; Humans; Individ och samhälle VIDSOC; Individual and Society VIDSOC; Male; Middle Aged; Obesity; Obesity - complications; Risk Factors; Time Factors; Weight Loss - physiology; Body mass index; Obesity; Cohort study; Bias; Dementia
• ISSN: 1552-5260; 1552-5279; 1552-5279
• DOI: 10.1016/j.jalz.2017.09.016

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. 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. Hazard ratios per 5-kg/m2 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. 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. •Data from 1.3 million adults from 39 prospective cohort studies were pooled for the analyses.•Higher BMI was associated with increased risk of dementia when the follow-up was long.•When follow-up was short, lower BMI was linked to increased dementia risk probably due to reverse causation.