Being underweight in mid to late life increases risk of dementia

Middle-aged and older people who are underweight are a third more likely to develop dementia than people of a similar age with a healthy body weight, according to a new study.

The research published in The Lancet Diabetes & Endocrinology journal found people with a Body Mass Index (BMI) of less than 20 kg/m2 are 34 per cent more likely to develop dementia than people of similar age with a healthy BMI. This increased risk of dementia persisted even 15 years after the underweight was recorded.

In the wake of the findings, study author Stuart Pocock, professor of medical statistics from the London School of Hygiene & Tropical Medicine, called 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.

“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.”

Study lead author Dr Nawab Qizilbash from OXON Epidemiology, said: “If increased weight in mid-life is protective against dementia, the reasons for this inverse association are unclear at present. Many different issues related to diet, exercise, frailty, genetic factors, and weight change could play a part.”

Dr Doug Brown, director of research and development at Alzheimer’s Society, urged caution over the findings, saying: “We don’t yet know enough about the link between body weight and dementia.

“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 study of almost two million people also reports that being underweight in later years could increase risk of developing the condition by a third.”

He added: “This mixed picture highlights the difficulty of conducting studies into the complex lifestyle risk factors for dementia and reinforces the need for further research so we can identify the most important risk factors. While the evidence on body weight and dementia is unclear, we know that people can make positive lifestyle choices to keep their brains healthy by taking regular exercise, not smoking and following a healthy balanced diet.”

Researchers based at the London School of Hygiene & Tropical Medicine and OXON Epidemiology analysed data from almost two million people in the Clinical Practice Research Datalink (CPRD), a large database of patient information recorded during routine general practice over nearly 20 years, representing around nine per cent of the UK population.