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Low BMI linked to Alzheimer’s disease in later life
22 November 2011
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Having a lower body mass index (BMI) in later life may increase your risk of Alzheimer’s disease, according to new research published in the journal Neurology.
The researchers were interested in investigating the ‘obesity paradox’ – a phenomenon whereby middle aged people with a high BMI are at high risk of Alzheimer’s disease, but conversely people with a high BMI in later life are at low risk of Alzheimer’s disease.
The researchers looked at Alzheimer’s disease risk in 405 elderly people using brain scans and Alzheimer’s disease biomarkers (substances in a person’s blood to indicate a disease). They found that people with a low BMI in later life had more biomarkers for Alzheimer’s disease and a greater amount of protein build-up in the brain (damage caused by the disease).
The researchers were unable to say whether Alzheimer’s disease caused the weight loss, or if early symptoms of the disease result in people being less able to look after themselves causing them to lose weight, for example not eating properly. They suggest that weight loss in old age could be used as an early indicator of the disease.
Dr Clive Bowman, Medical Director, Bupa Care Services, said: “It's difficult to know how to interpret these findings. In a study looking into the ‘obesity paradox’, the researchers have failed to see if anyone in the study did actually lose weight between middle age and later life. It's natural for people to lose body mass as they age and although the researchers acknowledge this, they fail to take it into account in their analysis. What they have found is what you’d expect as people get older, weight loss and an increased risk of Alzheimer’s disease.
"My advice is not to worry. There are a number of reasons for weight change in ageing, which can represent health gain or indeed illness. Simply losing a few pounds doesn’t mean you’re on the path to developing Alzheimer’s disease. Maintaining a healthy body weight and general fitness remains a cornerstone for maintaining the best possible wellbeing, and for some people losing or gaining weight may be helpful to improve fitness. At this stage that is the extent of sound medical advice."
The researchers took blood samples to measure Alzheimer’s disease biomarkers. Only a quarter of these people had scans to see if there was any damage to their brain. The researchers asked each person to fill out questionnaires about their mental state and assessed their risk of Alzheimer’s disease using a cognitive scale. Height and weight were measured at the start of the study to calculate BMI. When the researchers analysed the results they took into account age and sex.
Key facts
- Alzheimer's disease gradually damages the way the brain works, which affects a person's memory, ability to communicate, and their ability to make decisions and carry out their daily activities.
- The disease develops slowly, usually over many years. Treatments for Alzheimer's disease can't cure the condition but, for some people, treatment may slow down the development of the disease for a period of time.
- Alzheimer's disease is the most common cause of dementia and there are around 37 million people worldwide with dementia.
- BMI takes into account your weight and height and is, in general, a good indicator of how much body fat you have. It is calculated as: your weight in kilograms divided by the square of your height in metres.
How can we help you?
Find out more about Alzheimer’s disease
Read our dementia guide, including information on the different types of dementia, what to expect, where to get help and advice on choosing a suitable care home.
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Read the study
Vidoni ED, Townley RA, Honea RA, et al. Alzheimer disease biomarkers are associated with low body mass index. Neurology 2011; 77:1913. doi:10.1212/WNL.0b013e318238eec1
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