Lean Muscle May Prevent Alzheimer’s Disease

A major study published in the open access journal BMJ Medicine reveals that high amounts of lean muscle may protect against Alzheimer’s disease. According to the study’s authors, more research is needed to elucidate the underlying molecular mechanisms, as well as the clinical and public health implications.

Obesity has been linked to an increased risk of Alzheimer’s disease in multiple studies, which may be explained by the related increased inflammation, insulin resistance, and higher levels in fat tissue of the protein amyloid, which is damaging to brain health.

Lower amounts of lean muscle have also been linked to an increased risk of the condition, however it’s unclear whether this occurs before or after a diagnosis.

The researchers employed Mendelian randomization to explore, a strategy that employs genetic variants as proxy for a certain risk factor—in this case, lean muscle—to get genetic evidence in favor of a specific outcome—in this case, Alzheimer’s disease risk.

They used 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 7,329 people with and 252,879 people without Alzheimer’s disease, and 269,867 people taking part in a genes and intelligence study to validate their findings.

Bioimpedance was utilized to quantify lean muscle and fat tissue in the arms and legs, with the results adjusted for age, gender, and genetic ancestry.

There were 584 genetic variants associated with lean muscle mass; none were found in the APOE gene area, which is linked to the vulnerability of the disease. These genetic variations explained 10% of the difference in lean muscle mass between study participants’ arms and legs.

Higher (genetically proxied) lean muscle mass was associated with a slight, but statistically significant, reduction in the incidence of Alzheimer’s disease.

This finding was repeated in a larger sample of 7,329 persons with Alzheimer’s disease and 252,879 people without the condition, using different measurements of lean muscle mass—trunk and whole body.

Although lean mass was related with improved cognitive function, this association did not explain the protective effect of lean mass on the risk of this disease. Body fat was not connected with the risk of Alzheimer’s disease when adjusted for lean mass, but it was associated with lower cognitive task performance.

“These analyses provide new evidence supporting a cause-and-effect relation between lean mass and risk of Alzheimer’s disease,” say the researchers.

The findings also “refute a large effect of fat mass on the risk of this disease and highlight the importance of distinguishing between lean mass and fat mass when investigating the effect of adiposity measures on health outcomes,” they add.

But they 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 the disease after which modifications of lean mass might no longer reduce the risk.”

Similarly, it is unclear if increasing lean mass could alter Alzheimer’s disease pathology in patients with preclinical disease or mild cognitive impairment, they say.

However, they conclude that if future studies back their findings, “public health efforts to shift the population distribution of lean mass, potentially through campaigns to promote exercise and physical activity, might reduce the population burden of Alzheimer’s disease.”

Source Link