Midlife obesity and dementia: meta-analysis and adjusted forecast of dementia prevalence in the United States and China.

Objective: Obesity is a risk factor of dementia. Current forecasts of dementia prevalence fail to take the rising obesity prevalence into account.

Design And Methods: Embase and Medline were searched for observational studies on the association between overweight (BMI 25-30 kg/m(2)) or obesity (BMI > 30 kg/m(2)) and dementia and pooled the effect sizes by meta-analysis. The population attributable risk (PAR) was calculated for different time points and adjusted them for confounders. Based on current prevalence rates of dementia and demographic forecasts, patient numbers were calculated and adjusted by the growth rates of PAR.

Results: Compared to normal weight, midlife obesity increases the risk of dementia later in life (BMI 25-30: RR = 1.34 [95% CI 1.08, 1.66], BMI > 30: RR = 1.91 [1.4, 2.62]). If obesity is included into forecast models, the prevalence of dementia is estimated to be 7.1 million (6.9, 7.3) and 11.3 million (10.9, 11.7) for the United States in 2030 and 2050, respectively. In China, the estimate is 13.1 million (12.8, 13.3) in 2030 and 26.2 million (25.1, 27.4) in 2050. These figures are 9% and 19% higher for the United States and China, respectively, than forecasts that rely solely on the demographic change.

Conclusion: The past and ongoing increase in midlife obesity prevalence will contribute significantly to the future prevalence of dementia and public health measures to reduce midlife obesity are simultaneously primary prevention measures to reduce the risk of dementia.