Abstract
INTRODUCTION: Insufficient evidence exists on the sex-specific associations of body mass index (BMI) and weight change through midlife with dementia incidence, especially in Asian populations. METHODS: For 37,414 Japanese residents aged 40 to 59 years, BMIs at baseline (year 1990 or 1993) and 10-year follow-ups were obtained. Weight changes between baseline and 10-year follow-ups were determined. Disabling dementia incidence from 2006 to 2016 was ascertained using long-term care insurance (LTCI) certifications. Hazard ratios (HRs) were computed. RESULTS: Increased dementia risk was observed with obesity at baseline and with underweight at 10-year follow-ups. Weight loss after baseline was at greater risk than weight gain. No sex difference was observed. DISCUSSION: In both sexes, obesity in midlife increased the risk of developing dementia with increasing impacts of weight loss after midlife. A healthy body weight throughout adulthood is beneficial for dementia prevention. HIGHLIGHTS: Obesity in midlife is a risk factor for incident dementia.Weight loss is a bigger risk factor than weight gain in later midlife.Association of BMI and weight change in midlife with dementia does not vary by sex.