Body Mass Index Shows Potential Link to Dementia

There has been considerable research regarding the unhealthy risks associated with being overweight later in life. A recent study has shown that being underweight can also have a negative effect on a person’s life as they get older.

According to results of a study published in The Lancet Diabetes & Endocrinology, patients with a body mass index (BMI) under 20 kg/m² in their middle-aged years are one-third more likely to develop dementia than those with a healthy index. The results of the study also showed that obese people at the same time in their lives are 30% less likely to develop dementia than those with healthy levels.

The work was conducted by researchers at the London School of Hygiene & Tropical Medicine, and OXON Epidemiology in London. Part of the focus of their research was the Clinical Practice Research Datalink, which includes patient records dating back close to 20 years. According to a press release on the study that includes roughly 9% of the total population of the United Kingdom with researchers going through nearly 2 million records.

The average age of the patient pool was approximately 55 with an average BMI of 26.5 kg/m². Over the course of a 9-year study period more than 45,000 patients included in the study were diagnosed with dementia. The researchers noted that patients diagnosed as “underweight,” were 34% more likely to receive the diagnosis than those at healthy levels. The press release noted that the risk continued to increase, “even 15 years after the underweight was recorded.”

The results were even more encouraging for those who were diagnosed as obese, or having a BMI greater than 40 kg/m². This group was found to be 29% less likely to develop dementia. All data was based on the classification of 25 kg/m² being considered healthy weight.

Looking at the data the researchers determined that the risk of developing dementia was not affected “by the decade in which the participants were born, nor by their age at diagnosis,” according to the release. It was also determined that other factors including alcohol use and smoking “made little difference to the results.”

Stuart Pocock, an author of the study, said the results showed a need for “doctors, public health scientists, and policy makers to re-think how to best identify who is at high risk of dementia.” He added, “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.”

The results, according to Pocock, could also affect other areas of the study of 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.”

While identifying the potential connection is important, Nawab Qizilbash, MD, from OXON said it was just part of the overall equation. “If increased weight in mid-life is protective against dementia, the reasons for this inverse association are unclear at present,” he said. “Many different issues related to diet, exercise, frailty, genetic factors, and weight change could play a part.”

Deborah Gustafson, a professor from SUNY Downstate, noted in a linked comment that, “The published literature about BMI and dementia is equivocal.” Gustafson noted that “some studies report a positive association between high mid-life BMI and dementia, where as others do not.”

“Many considerations are needed in the assessment of the epidemiology of the association between BMI and late-onset dementia, as is the case for many recorded associations involving late-life disorders,” Gustafson added. “To understand the association between BMI and late-onset dementia should sober us as to the complexity of identifying risk and protective factors for dementia.”

The professor from New York also cautioned that “the report by Qizilbash and colleagues is not the final word on this controversial topic.”