Dementia charities recommend maintaining a healthy weight to lower dementia risk, yet some studies propose that obesity could potentially offer protection against dementia. Obesity is strongly linked to dementia, especially when individuals are obese in middle age, increasing their risk of dementia later in life.
Obesity harms brain blood vessels increasing dementia risk
Obesity is known to harm the small blood vessels in the brain and is linked to conditions like diabetes, high blood pressure, and chronic inflammation, which increase dementia risk. However, there are contradictions in the evidence. Despite rising obesity rates, dementia rates have fallen in the West. Some studies even suggest an “obesity paradox,” where obesity seems to lower dementia risk.
The challenge of establishing a causal link between obesity and dementia stems from the broad definitions of both conditions and limitations in available data. Ideally, a randomized trial would be conducted where participants are randomly assigned to either become obese or not, but such a study is not feasible.
Obese individuals potentially facing a higher risk of dementia later in life suggests causation, though conducting such trials is impractical and unethical due to time, expense, and ethical concerns. Consequently, studies resort to observational data, tracking large groups over time to examine the long-term relationship between obesity and dementia.
Individuals with early dementia lose weight due to disease
Observational studies, while valuable, are prone to biases, complicating result interpretation. In dementia research, “reverse causation” is a notable bias, especially with older subjects and short follow-up times. This phenomenon suggests that individuals in early dementia stages may lose weight due to the disease, potentially explaining the obesity paradox.
“Confounding bias” is another issue where the association between obesity and dementia may be influenced by another related factor, such as childhood intelligence. Studies have shown that childhood intelligence, when considered, can potentially clarify associations attributed to obesity in later life. Recent research suggests that lower childhood intelligence might account for the slightly worse cognitive skills observed in middle-aged individuals with obesity compared to those with normal weight.
