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Obesity, often linked to dementia risk, seems to be a result of its impact on blood vessels, diabetes, and inflammation. However, some research suggests it may paradoxically offer protection against dementia.Story highlights
People are typically counselled to keep a healthy weight in order to lower their risk of dementia. However, other research indicates that obesity may potentially offer a defence against dementia. What is the truth behind it?
At first glance, the research that links obesity to dementia seems solid. It is generally accepted that obesity throughout middle age raises the risk of dementia in later life.
Obesity harms the brain's small blood arteries and is a key contributor to diabetes, high blood pressure, and chronic inflammation—all conditions that have been repeatedly associated with an increased risk of dementia.
However, if dementia is indeed caused by obesity, then why have dementia rates declined in the west in recent decades while the number of obese individuals has increased?
An "obesity paradox" wherein being fat seems to be related with a lower risk of dementia, has been shown in a number of studies.
Due to data constraints, scientists find it difficult to establish a cause-and-effect link. While a randomised experiment would be ideal, but assigning people to be obese is unethical.
The majority of research is based on observational studies, which include long-term follow-up on large populations. However, these studies may be biased.
"Reverse causation" is an issue, especially when researching elderly persons. People in the early stages of dementia may lose weight as a result of the condition, rather than the reverse. This may explain the obesity paradox.
Another issue is called "confounding bias." A third factor associated with both obesity and dementia might explain the apparent relationship between the two. One example is childhood intelligence, which is rarely assessed in these research.
Researchers found that although there was a clear association between higher levels of obesity and lower cognitive skills in midlife, this probably wasn't because one was causing the other.
Researchers discovered that, while there was a strong link between greater levels of obesity and decreased cognitive skills in midlife, it was unlikely that one caused the other. Instead, it was probably because a third component (childhood intelligence) was linked to both.
To summarise, the research of obesity and dementia is complicated. While maintaining a healthy weight is beneficial to general health, the relationship to dementia risk is uncertain.
(With inputs from agencies)
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