Although past research has associated obesity with increased risk of dementia, a new study – deemed the largest ever to assess the link between body mass index and dementia risk – suggests obesity could actually be a protective factor against the condition, while people who are underweight may be at increased risk.

A large retrospective cohort study, published in The Lancet Diabetes and Endocrinology, has revealed a surprising association between being underweight in mid-life and late-life, and increased risk of dementia.

The study assessed the medical records of almost 2 million people in the UK in order to gain a better understanding of how obesity affects dementia risk. The researchers found that, compared with adults who had a healthy BMI (between 20-25 kg/m2), those who were underweight – defined in this study as a BMI less than 20 kg/m2 – during middle age were 34% more likely to be diagnosed with dementia. This increased risk remained for 15 years after adults’ underweight status was recorded.

The team notes that participants with a BMI of less than 18.5 kg/m2 are usually classed as underweight, but the threshold was raised in this study to allow comparisons with past studies, which have defined a BMI of less than 20 kg/m2 as underweight.

The researchers also found that middle-aged adults’ risk of dementia steadily reduced as their BMI increased. Compared with adults who had a healthy BMI, those who were severely obese (BMI greater than 40 kg/m2) were 29% less likely to develop dementia. The team says their results remained even after accounting for factors associated with increased dementia risk, including smoking and alcohol consumption. In addition, the results were not affected by adults’ age at dementia diagnosis or the decade in which they were born, according to the researchers.

Source: Medical News Today


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