What Being Too Thin Might Do to Your Brain

Dementia risk tied to being underweight in middle adulthood

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) The dangers of being too heavy are well-known, but does being too thin pose any risks? In fact, it could pose some risks to your mental health.

A new study found that being underweight during middle adulthood may lead to a higher risk of dementia later on.

This study assessed weight using body mass index (BMI). BMI is a measure of body fat based on height and weight.

"An understanding of the association of BMI (measured in [kilogram/square meter]) with dementia is a public health priority because the number of people affected by dementia worldwide is expected to rise from 30 million in 2010, to 106 million in 2050, and the prevalence of obesity is also increasing worldwide," explained the study authors, led by Nawab Qizilbash, MRCP, of the London School of Hygiene & Tropical Medicine.

Dr. Qizilbash and team aimed to explore the relationship between weight in middle adulthood and dementia in later years. To do so, they looked at data from the UK Clinical Practice Research Datalink, which involved nearly 2 million adults aged 40 or older.

These patients were 55 years old on average at the study's start and had no history of dementia. BMIs were recorded between 1992 and 2007, when the patients entered the study.

The follow-up lasted for an average of nine years, during which time 45,507 patients were diagnosed with dementia. Dementia is a slowing in brain function marked by problems with memory, thinking and reasoning, as well as personality changes.

When looking at different weight groups, Dr. Qizilbash and team found that people who had a BMI of less than 20 (considered underweight) had a higher risk of dementia.

The underweight patients were 34 percent more likely to develop dementia during the follow-up than people of a healthy weight.

Dementia risk seemed to decrease as weight increased, even beyond the healthy weight range. Very obese patients with a BMI above 40 had a 29 percent lower dementia risk than people with a BMI in the healthy range.

"... Our study shows a substantial increase in the risk of dementia over two decades in people who are underweight in mid-life and late-life," Dr. Qizilbash and team wrote.

A better understanding of why the heavier patients had a lower risk of dementia could help in the development of treatments for dementia down the road, Dr. Qizilbash and team noted.

This study was published April 10 in The Lancet Diabetes & Endocrinology. Dr. Qizilbash and team disclosed no funding sources or conflicts of interest.

Review Date: 
April 9, 2015
Last Updated:
April 14, 2015