Obesity and dementia risk

About obesity

Obesity is when a person has an excess of body fat that affects their health.

The NHS define obesity as having a body mass index (BMI) of 30 or above. This is measured by dividing an adult’s weight in kilograms by their height squared (in m).

Keeping a healthy weight

The two most important things to do to lose weight are to exercise regularly and to eat healthily.

Eating a healthy, balanced diet may help to achieve a healthy weight. No single ingredient, nutrient or food can improve health by itself. Instead, eating a range of different foods in the right proportions is what makes a difference.

By eating a balanced diet you are more likely to get all the nutrients you need to stay healthy. The NHS Eatwell guide shows what food groups make up a balanced diet and roughly how much of each is needed to stay healthy.

Taking regular physical exercise can also help to achieve a healthy weight. It is also one of the best things that you can do to reduce your risk of getting dementia.

‘Moderate intensity’ aerobic activity is anything that makes you breathe faster and feel warmer. ‘Vigorous’ activity is anything that makes you sweat or get out of breath after a while, making it difficult to talk without pausing for breath.

In general, one minute of vigorous activity is equal to two minutes of moderate intensity activity. The official UK recommendation is to try to do at least 150 minutes of moderate intensity activity each week or 75 minutes of vigorous activity. You can break this activity up into smaller sessions.

How obesity affects the brain

The size of a person’s brain starts to decrease naturally as they age. However, research has shown a relationship between BMI and brain size in people around the age of 60. The research found that the higher someone’s BMI the smaller their brain was.

The increased brain shrinkage associated with obesity has been suggested by some to age the brain by around 10 years.

Research has shown also that the areas of the brain that start to shrink more in Alzheimer’s disease also shrink in people who are obese.

Obesity can also lower a person’s resilience to the damage in the brain that Alzheimer’s disease causes, leading to worse symptoms and faster disease progression.

Obesity can also lead to chronic inflammation in the body, which can have knock-on effects on the brain. Inflammation in the brain is linked to dementia as it can cause the over-activation of immune cells in the brain which leads them to damage the brain’s nerve cells.

Can weight loss help with dementia?

The link between dementia and weight loss is complex.

Studies have shown that healthy weight loss in midlife can improve memory skills and attention. In people who were overweight (with a BMI of greater than 25) losing 2kg was enough to benefit them.

These effects were measured over a few months, and the long-term effects were not recorded. The research only looked at memory and thinking skills and did not measure dementia risk itself. Other research shows that people who maintain a healthy weight are more resilient to the changes in the brain that are caused by Alzheimer’s disease.

However the relationship between weight change and dementia risk is complicated. Weight loss may be an early feature of dementia in some people. This is because dementia can affect a person’s ability to manage their nutrition leading to unintentional weight loss.

Weight loss is also common in the later stages of dementia, due to loss of appetite or difficulties with chewing.

In general, while maintaining a healthy weight may reduce a person’s risk of developing dementia, it does not guarantee protection against dementia. This is because there are many other genetic and lifestyle factors that contribute to dementia risk.