Middle-Aged Underweight Adults May be at Risk for Dementia

Middle-aged underweight adults may be at risk for developing dementia, according to a new study.

Those who are underweight have a Body Mass Index (BMI) less than 20 kg/m, and a group of UK researchers say that these people are a third more likely to develop dementia than people of similar age with a healthy BMI.

The findings, published in The Lancet Diabetes & Endocrinology journal, come from the largest ever study to examine the statistical association between BMI and dementia risk.

Interestingly, the results also show that middle-aged obese people (BMI greater than 30 kg/m2) are nearly 30 percent less likely to develop dementia than people of a healthy weight. This goes against the previous notion that obesity actually leads to an increased risk of dementia.

To better understand the association between weight and dementia risk, researchers based at the London School of Hygiene & Tropical Medicine and OXON Epidemiology analyzed the medical records of nearly two million UK patients, aged 55 years old on average, and with a BMI of 26.5 kg/m2. During the 9-year follow-up, nearly 50,000 people were diagnosed with dementia.

Specifically, those who were underweight in middle age were a third (34%) more likely to be diagnosed with dementia than those of a healthy weight. What's more, this increased risk of dementia persisted even 15 years after the underweight was recorded.

In addition, participants' BMI at middle age increased, the risk of dementia reduced. In fact, very obese people (BMI greater than 40 kg/m2) were 29 percent less likely to get dementia than people in the normal weight range.

It should be noted that the results simply found an association between underweight individuals and increased dementia risk, and the study does not establish and cause-and-effect relationship. While future research is needed to better understand these findings, they help to shed light on possible risk factors for dementia.

"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," researcher Stuart Pocock concluded in a statement.

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