Underweight people are one-third more likely to develop dementia than those of a healthy weight, a new study finds.
It also found that very obese people are 30% less likely to develop dementia than those with a healthy weight.
This surprising conclusion comes from the largest ever study of middle-aged people’s dementia risk and body weight.
The findings fly in the face of previous research suggesting a positive connection between obesity and dementia.
Professor Stuart Pocock, from the London School of Hygiene & Tropical Medicine, who led the study, said:
“Our results suggest that doctors, public health scientists, and policy makers need to re-think how to best identify who is at high risk of dementia.
We also need to pay attention to the causes and public health consequences of the link between underweight and increased dementia risk which our research has established.
However, our results also open up an intriguing new avenue in the search for protective factors for dementia — if we can understand why people with a high BMI have a reduced risk of dementia, it’s possible that further down the line, researchers might be able to use these insights to develop new treatments for dementia.”
For the research data was analysed from nearly two million people.
They were followed up over almost a decade to check their weight and any dementia diagnosis.
The results showed that very obese people (those with a BMI over 40) were 29% less likely to develop dementia than those of a normal, healthy weight.
Below a healthy weight (a BMI of 25), the dementia risk increased.
Above a healthy weight, though, the dementia risk continued to decrease, but more slowly.
Dr Nawab Qizilbash, the study’s first author, said:
“The reasons why a high BMI might be associated with a reduced risk of dementia aren’t clear, and further work is needed to understand why this might be the case.
If increased weight in mid-life is protective against dementia, the reasons for this inverse association are unclear at present.
Many different issues related to diet, exercise, frailty, genetic factors, and weight change could play a part.”
The research was published in The Lancet Diabetes & Endocrinology journal (Qizilbash et al., 2015)
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