Lean muscle may guard against Alzheimer's disease.

High levels of lean muscle might protect against Alzheimer's disease, suggests a large study published in the open-access journal BMJ Medicine. Lower levels of lean muscle have also been associated with a heightened risk of the disease, but it’s not clear if this might precede or succeed a diagnosis.

To try and find out, the researchers used Mendelian randomization, a technique that uses genetic variants as proxies for a particular risk factor—in this case, lean muscle—to obtain genetic evidence in support of a particular outcome—in this study, Alzheimer’s disease risk.

They drew on 450, 243 UK Biobank participants; an independent sample of 21,982 people with, and 41,944 people without, Alzheimer’s disease; a further sample of 7329 people with, and 252,879 people without, Alzheimer’s disease to validate the findings; and 269,867 people taking part in genes and intelligence study.

Bioimpedance—an electric current that flows at different rates through the body depending on its composition—was used to estimate lean muscle and fat tissue in the arms and legs, the results of which were adjusted for age, sex, and genetic ancestry.

On average, higher (genetically proxied) lean muscle mass was associated with a modest, but statistically robust, reduction in Alzheimer’s disease risk.

Reference: Genetically proxied lean mass and risk of Alzheimer’s disease: mendelian randomization study, BMJ Medicine, DOI 10.1136/bmjmed-2022-000354