Obesity and Longer Term Risks of Dementia in 65-74 Year Olds

Background overweight or obesity at ages <65 years associates with increased dementia incidence, but at 65 years estimates are paradoxical. Weight loss before dementia diagnosis, plus smoking and diseases causing weight loss may confound associations. Objective to estimate weight loss before dementia diagnosis, plus short and longer-term body mass index associations with incident dementia in 65-74 year olds within primary care populations in England. Methods we studied dementia diagnosis free subjects: 257,523 non-smokers without baseline cancer, heart failure or multi-morbidity (group A) plus 161,927 with these confounders (group B), followed 14.9 years. Competing hazard models accounted for mortality. Results in group A, 9,774 were diagnosed with dementia and in those with repeat weight measures, 54% lost 2.5 kg during 10 years pre-diagnosis. During <10 years obesity (30.0 kg/m(2)) or overweight (25.0 to <30.0) were inversely associated with incident dementia (versus 22.5 to <25.0). However, from 10 to 14.9 years, obesity was associated with increased dementia incidence (hazard ratio [HR] 1.17; 95% CI: 1.03-1.32). Overweight protective associations disappeared in longer-term analyses (HR, 1.01; 95% CI: 0.90-1.13). In group B, (n = 6,070 with incident dementia), obesity was associated with lower dementia risks in the short and longer-term. Conclusions in 65-74 year olds (free of smoking, cancer, heart failure or multi-morbidity at baseline) obesity associates with higher longer-term incidence of dementia. Paradoxical associations were present short-term and in those with likely confounders. Reports of protective effects of obesity or overweight on dementia risk in older groups may reflect biases, especially weight loss before dementia diagnosis.