text: Being underweight in mid-life could increase your risk of dementia, claim researchers. A new study shows you are a third more likely to be diagnosed with diseases such as Alzheimer's than those of a healthy weight. Obese people appear to be protected against dementia, with a risk around 30 per cent lower than those of healthy weight. The findings contradict many previous studies which have suggested that being fat – with a high Body Mass Index (BMI) - could raise the risk. A new study shows underweight people are a third more likely to be diagnosed with diseases such as Alzheimer's than those of a healthy weight (file photo) Study author, Professor Stuart Pocock, from the London School of Hygiene and Tropical Medicine, said doctors and policymakers may have to re-think how to best identify those at high risk of dementia. He said '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.' Other experts said more research was needed, and the way GPs used to diagnose dementia may have skewed the results. Researchers based at the London School of Hygiene and Tropical Medicine and Oxon Epidemiology, also in London, analysed patient information recorded during routine general practice over nearly two decades. Data on 1,958,191 patients aged 55 on average with a BMI of 26.5 on average - just within the range usually classed as overweight - were examined. BMI is assessed by comparing height to weight, in a calculation which divides weight in kilos by height in metres squared. A healthy score is between 18.5 and 24.99 – above is overweight and obese. The study regarded BMI of less than 20 as underweight. After nine years follow-up, 45,507 people were diagnosed with dementia. Researchers found people who were underweight in middle age were 34 per cent more likely to be diagnosed with dementia than those of a healthy weight. The findings contradict many previous studies which have suggested that being fat – with a high Body Mass Index (BMI) - could raise the risk (file photo) As people's BMI increased, the risk of dementia fell, with very obese people having a BMI greater than 40 less likely to develop the condition than those of normal weight. The link was not affected by the decade in which patients were born, age at diagnosis, alcohol use or smoking. The new research was published in The Lancet Diabetes And Endocrinology journal (must credit). Dr Nawab Qizilbash, from Oxon Epidemiology in London, said the reasons why high BMI might lead to a lower risk of dementia are not clear. 'Many different issues related to diet, exercise, frailty, genetic factors and weight change could play a part' he said. Prof Tom Dening, Professor of Dementia Research, University of Nottingham, said limitations of the study included poor dementia diagnosis rates by GPs at the time. He said 'It is plausible that faced with a grossly obese patient, the average GP may have concentrated on the obvious medical risks and paid less attention to the cognitive issues than they might have done with a comparable patient of normal weight. 'Or maybe the GP didn't refer them to a memory clinic but sent them to see a gastroenterologist or diabetologist instead. 'In other words, the study may be telling us something about the diagnostic practices of GPs, as much about the natural history of metabolic disease and dementia.' Dr Doug Brown, Director of Research and Development at Alzheimer's Society, said 'Previous research has suggested that being overweight in midlife increases risk of developing the condition and yet this study suggests that it may actually be protective. 'This mixed picture highlights the difficulty of conducting studies into the complex lifestyle risk factors for dementia and reinforces the need for further research. Dr Simon Ridley, Head of Research at Alzheimer's Research UK, said 'There is currently no sure-fire way to prevent dementia. 'In the meantime, evidence suggests that we can reduce the risk by eating a healthy, balanced diet, exercising regularly, not smoking, and keeping blood pressure in check.
target: Underweight people are also more likely to be diagnosed with Alzheimers .
  Obese person is 30 per cent less likely to get dementia than healthy person .
  This could help scientists develop new treatments, researchers have said .