Body Weight

Obesity in midlife increases the risk of dementia.

Obesity in midlife is associated with an increased risk of developing cognitive impairment and dementia.  To reduce the risk of dementia, all adults should try to maintain a healthy body weight throughout life and avoid ‘middle age spread’.

What’s the evidence that body weight affects dementia risk?

Research consistently shows that people who are obese in midlife are on average more likely to develop dementia compared to those of normal body weight.  This association is not found in people at old age because dementia is associated with weight loss.

Someone who is obese has a body mass index (BMI) of more than 30.  Your BMI is calculated by dividing your weight in kilograms by your height in metres squared (m2).  A BMI of 18.5 to 25 is considered healthy; between 25 and 30 is overweight.  A BMI less than 18.5 means you are underweight, and research suggests that this may also be associated with an increased risk of developing dementia.

It seems that being overweight (BMI between 25 and 30) only slightly increases dementia risk.  However, being obese (BMI greater than 30) is clearly a risk factor as demonstrated by several research studies.  Central obesity, having a large waist, has been particularly associated with a higher dementia risk in recent studies.

It is not easy for many people to maintain a healthy body weight, but doing so is very important for your heart and brain health.  So to reduce your risk of dementia, stroke and heart disease ask your doctor to check your weight and make sure you follow their treatment advice if it is found to be too high.

Evidence rating for obesity  

The relationship between body weight and dementia risk is complicated as it changes with age.

Taking the evidence as a whole we can conclude that obesity during midlife does increase dementia risk. This evidence has been established in meta-analyses.

What is lacking is proof that losing weight for those who are obese will reduce dementia risk.

The evidence suggests that:

  • obesity during midlife increases the risk of later developing dementia
  • body mass index decreases as dementia is developing, and being underweight at late life is therefore associated with increased incidence of dementia

How does obesity affect dementia risk?

Obesity is closely linked to high blood pressure, high cholesterol and diabetes, all of which increase the risk of dementia.  Obesity increases the risk of cardiovascular disease and this increases the risk of dementia.  Adipose tissue (fat) secretes hormones and other factors that might directly affect the health of the brain and may increase the production of plaques that are thought to cause Alzheimer’s disease.

How to maintain a healthy body weight

Regular physical exercise can help reduce your weight and has lots of health benefits. See our physical activity pages.

Eating a healthy, balanced diet helps maintain a healthy weight.  Choose foods low in saturated fat, wholegrain breads and cereals, legumes, vegetables and fruits.  See our diet pages.

Too much alcohol can increase your weight.  See our alcohol page.

There are genetic factors that influence your body weight, so some people who try to do all the right things might still struggle to maintain a healthy weight and may need medical advice or treatment.

If concerned about your weight, speak to your doctor.  They can advise you of the best approach to losing weight for you.  Avoid fad diets that promise rapid weight loss because these can be dangerous.

For further information, visit the following websites:

The Measure Up campaign website provides information and resources and links to further information on weight, physical activity and healthy eating.

The Department of Health and Ageing Healthy Weight website provides information, tips and resources for maintaining a healthy weight.

The Heart Foundation provides information for consumers on weight, physical activity and healthy eating.



Your Brain Matters was supported by funding from the Australian Government under the Chronic Disease Prevention and Service Improvement Fund from July 2012 to June 2015.


The National Dementia Helpline: 1800 100 500

Alzheimer's Australia would like to acknowledge the Aboriginal people as the traditional custodians and carers of the country of Australia. We acknowledge and respect the Aboriginal people of Australia's relationship with country and their cultural and spiritual beliefs.