Weili Xu and colleagues, Karolinska Institute, Stockholm, Sweden, show that both midlife overweight with a BMI of 25 or above and obesity independently increase the risk of dementia and of Alzheimer and vascular dementia. Genetic and early-life environmental factors may contribute to the adiposity dementia association.

In a study of 8,534 both identical and fraternal twins aged 65 and older in Sweden, they found that individuals diagnosed with Alzheimer’s disease or vascular dementia were 70 % more likely to have been overweight when they were middle-aged. About 30 % of the individuals were overweight or obese, about 4 % of the participants were diagnosed with Alzheimer’s disease or vascular dementia.

The mechanisms that link the two conditions are still unclear. The researchers assume that being overweight in midlife may reflect a lifetime exposure to an altered metabolic and inflammatory state, which has been linked to cognitive faltering. Adipose tissue is the largest endocrine organ and secretes inflammatory cytokines and growth hormones; some of them – such as leptin, interleukin-6 and C-reactive protein – may affect cognitive functioning.

• Midlife overweight and obesity increase late-life dementia risk: A population-based twin study,
  W. L. Xu, A. R. Atti, M. Gatz, N. L. Pedersen, B. Johansson, L. Fratiglioni,
  Neurology 2011.
  DOI: 10.1212/WNL.0b013e3182190d09