Being too thin in middle age might be bad for brain health later in life, a new study suggests. The findings contradict previous work that has found obesity increases the risk of developing dementia.
Researchers from the London School of Hygiene and Tropical Medicine found that people with a BMI [body mass index] below 20, in their 40s, 50s and 60s were 34% more likely to be diagnosed with dementia up to 15 years later, compared with people of a healthy weight.
The study, published in the Lancet, analysed health records from two million people in the UK.
Lead author Nawab Qizilbash, a clinical epidemiologist, said the reasons were not clear. The paper speculates that factors such as diet, exercise, frailty, weight changes and deficiencies in vitamins D and E might play a role.
But Qizilbash said the findings were not a reason to be overweight.