Body weight and dementia risk – the evidence
Obesity, particularly central obesity, at midlife is associated with increased risk of later developing dementia [1]. Whether midlife weight loss for those who are obese can reduce the risk of late life dementia has not yet been determined.
In early old age (65 to 75 years), there is a U-shaped relationship between BMI and dementia risk, with increased risk found for those who are underweight or obese [1].
In late life (after 75 years), lower BMI and weight loss have been associated with an increased risk of dementia [1]. Weight loss may precede dementia onset by more than 10 years.
A recent review summarised the findings of the complex relationship between weight and dementia across the lifespan as follows [1]:
- central adiposity in middle age predicts dementia in old age
- the relation between high adiposity and dementia is attenuated with older age
- waist circumference in old age, a measure of central adiposity, may be a better predictor of dementia than BMI
- lower BMI predicts dementia in the elderly
- weight loss may precede dementia diagnosis by decades
While there is still more to learn, the available evidence suggests that maintaining a healthy weight over the life course is a strategy likely to optimise both body and brain health. There is clinical trial evidence that weight loss lowers blood pressure, improves blood lipids and insulin resistance, and positively affects other factors associated with cardiovascular and dementia risk.
How does excess weight impact on dementia risk?
There are a number of potential mechanisms by which obesity may increase dementia risk [1]. Insulin resistance and hyperinsulemia can result from obesity and may play a role in reducing beta amyloid clearance from the brain, increasing the risk of Alzheimer’s disease. Adipose tissue produces adipokines and cytokines, related to hyperinsulemia and inflammation that in turn have effects on the brain. Obesity is also associated with increased risk for cardiovascular and cerebrovascular disease, which increase the risk of dementia.
References
- Luchsinger JA & Gustafson DR. Adiposity and Alzheimer’s disease. Current Opinion in Clinical Nutrition and Metabolic Care, 2009, 12:15-21.
