Experts say whether obesity increases the risk of dementia Fitness and health13:30 | 03 May 2024

At first glance, the evidence linking obesity and dementia seems convincing. For example, it is known that obesity in midlife is associated with an increased risk of dementia in later life. We also know that obesity damages the small vessels that supply blood to the brain and is a major cause of chronic inflammation, which has been repeatedly linked to the risk of high blood pressure, diabetes, and dementia.

But not everything is that simple. If obesity really causes dementia, why are the number of obese people increasing while the number of people with the disease decreases? So why do many studies report evidence of the “obesity paradox,” in which obesity is associated with a reduced risk of dementia?

When conducting much of this work, scientists rely on data from observational studies. This involves following a large group of people over time to examine long-term links between obesity and dementia.

However, observational studies can be biased, making the results difficult to understand. For example, there is an error called “reverse causality”. People who already had early-stage dementia when the study started may have lost weight over time for this reason, and not the other way around. This is believed to be the basis of the obesity paradox.

Another common problem is “confusing bias.” Here the apparent link between obesity and dementia stems from another indicator that is associated with both. One of these is human intelligence in childhood. People with low intelligence as children have a higher risk of becoming obese as they get older and are more likely to have the same intelligence level as adults.

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