Higher levels of lean muscle may protect against Alzheimer’s disease

Having high levels of lean muscle may reduce your chances of developing Alzheimer’s disease, research suggests.

Based on genetic data, the study found that people with lifelong, higher lean muscle mass had a 12 per cent lower risk of Alzheimer’s disease, and better cognitive performance.

The findings suggest lean mass might be a protective factor for Alzheimer’s disease, the researchers said.

But further research is needed to investigate the clinical and public health implications of the findings.

Obesity has been associated with an increased risk of Alzheimer’s disease in many studies.

While lower levels of lean muscle have also been linked to a greater risk of the disease, it is not clear if this comes before or after a diagnosis.

To try to find out, the researchers used a genetic prediction technique called Mendelian randomisation, to obtain data on the link between lean muscle and Alzheimer’s.

They drew on information from 450,243 people in the UK Biobank study to validate the findings.

They took an independent sample of 21,982 people with Alzheimer’s and 41,944 people without; and a second sample of 7,329 people with the disease and 252,879 people without.

The researchers estimated lean muscle and fat tissue in the arms and legs, taking into consideration age, sex and genetic ancestry.

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

This finding was replicated in the second sample, using different measures of lean muscle mass – trunk and whole body.

Lean mass was also associated with better performance on cognitive tasks, but this association did not explain the protective effect of lean mass on Alzheimer’s disease risk, researchers say.

Body fat was also not associated with the risk of Alzheimer’s disease, but it was associated with poorer cognitive task performance.

“These analyses provide new evidence supporting a cause-and-effect relation between lean mass and risk of Alzheimer’s disease,” said the authors of the study, which was published in BMJ Medicine.

They said the findings also “refute a large effect of fat mass on the risk of Alzheimer’s disease and highlight the importance of distinguishing between lean mass and fat mass when investigating the effect of adiposity measures on health outcomes”.

But the authors caution: “Our findings need to be replicated with independent lines of complementary evidence before informing public health or clinical practice.

“Also, more work is needed to determine the cut-off values for age and degree of pathology of Alzheimer’s disease, after which modifications of lean mass might no longer reduce the risk."