Does Obesity Protect Against Dementia? Science Says It's Complicated

Dementia charities recommend maintaining a healthy weight for brain health. However, some studies suggest obesity might protect against dementia, according to Science Alert.

The link between obesity and dementia seems clear. Obesity in midlife increases dementia risk later. Obesity damages blood vessels in the brain and contributes to high blood pressure, diabetes, and inflammation, all linked to dementia, as per the news report.

But here's the twist: dementia rates are falling in the West while obesity rates rise. Additionally, some studies show an "obesity paradox," where obesity is linked to a lower dementia risk.

Scientists struggle to establish a cause-and-effect relationship due to limitations in the data. Ideally, a randomised trial would be conducted, but assigning people to be obese is unethical.

Most research relies on observational studies, following large groups of people for a long time. However, these studies can be biassed.

"Reverse causation" is a concern, particularly when studying older adults. People in the early stages of dementia might lose weight due to the disease, not the other way around. This could explain the obesity paradox.

Another issue is "confounding bias." An apparent link between obesity and dementia could be caused by a third factor related to both. One example is childhood intelligence, rarely measured in such studies.

Recent research suggests that lower childhood intelligence might explain why obese middle-aged adults have slightly worse cognitive skills. This doesn't mean obesity causes worse cognition, but rather that a third factor, low childhood intelligence, might influence both.

In conclusion, the science of obesity and dementia is complex. While maintaining a healthy weight is important for overall health, the link to dementia risk remains unclear.