Middle Aged and Underweight? You’re a Third More Likely to Develop Dementia Middle-aged people who are underweight (with a Body Mass Index [BMI] less than 20 are a third more likely to develop dementia than people of similar age with a healthy BMI, according to research published in The Lancet Diabetes & Endocrinology journal. The findings, which come from the largest ever study to examine the statistical association between BMI and dementia risk, also show that middle-aged obese people (BMI greater than 30 kg/m2) are nearly 30% less likely to develop dementia than people of a healthy weight, contradicting findings from some previous research, which suggested that obesity leads to an increased risk of dementia. Researchers based at the London School of Hygiene & Tropical Medicine, and OXON Epidemiology, both in London, UK, analysed data from the Clinical Practice Research Datalink (CPRD), a large database of patient information recorded during routine general practice over nearly 20 years, representing around 9% of the UK population. The researchers analzsed the medical records of nearly two million (1,958,191) people with an average (median) age of 55 years at the start of the study period, and an average (median) BMI of 26.5 kg/m2, just within the range usually classed as overweight.åÊ During an average (median) of nine years follow-up, nearly fifty thousand (45,507) people were diagnosed with dementia. People who were underweight in middle age were a third (34%) more likely to be diagnosed with dementia than those of a healthy weight, and this increased risk of dementia persisted even 15 years after the underweight was recorded. The association between BMI and dementia risk wasnÛªt affected by the decade in which the participants were born, nor by their age at diagnosis. Adjusting for confounding factors known to increase the risk of dementia, such as alcohol use or smoking, made little difference to the results. According to study author Professor Stuart Pocock from the London School of Hygiene & Tropical Medicine, ÛÏOur 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.åÊ 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.åÊ However, our results also open up an intriguing new avenue in the search for protective factors for dementia ÛÒ if we can understand why people with a high BMI have a reduced risk of dementia, itÛªs possible that further down the line, researchers might be able to use these insights to develop new treatments for dementia.Û