Does obesity increase risk of dementia? There isn’t enough evidence so far

Many dementia charities advise people to maintain a healthy weight to reduce their risk of dementia. But some studies have suggested that obesity might actually protect against dementia. What does the science say?

The evidence linking obesity to dementia does at first appear to be convincing. For example, we know that being obese in middle age is associated with an increased risk of developing dementia in later life.

We also know that obesity damages the tiny vessels supplying blood to the brain, and is a major cause of high blood pressure, diabetes and chronic inflammation, all of which have been repeatedly linked to dementia risk.

However, the picture is not that clear. For example, if obesity really does cause dementia, why have dementia rates been falling in the west in recent decades at the same time as the number of obese people has been increasing? And why have several studies reported evidence of something termed an “obesity paradox”, where being obese appears to be associated with a reduced risk of dementia?

Putting aside the longstanding problem of defining what we mean when we refer to obesity and dementia (both of which are relatively broad terms for conditions that can be defined in different ways), much of the difficulty in establishing whether one causes the other arises from limitations...

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