Increased lean muscle mass protects against Alzheimer’s disease

Research stated that high levels of lean muscle may guard against Alzheimer's disease. To fully understand the underlying molecular pathways and the implications for both clinical and public health, more study is nonetheless required. The study was made public in BMJ Medicine.
A higher risk of the disease has also been associated with lower levels of lean muscle, however it's unclear whether this happens before or after a diagnosis. Mendelian randomisation, a method that uses genetic variants as proxies for a particular risk factor—in this example, lean muscle—to get genetic evidence in support of a given outcome—in this case, risk of Alzheimer's disease—was used by the researchers to find out.
Numerous studies have found a correlation between obesity and an increased risk of Alzheimer's disease, which may be explained by the increased inflammation, insulin resistance, and higher amounts of the protein amyloid in adipose tissue, which is detrimental to brain function.
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.
Some 584 genetic variants were associated with lean muscle mass; none was located in the APOE gene region associated with vulnerability to Alzheimer's disease. These genetic variants combined explained 10% of the difference in lean muscle mass in the arms and legs of the study participants.
On average, higher (genetically proxied) lean muscle mass was associated with a modest, but statistically robust, reduction in Alzheimer's disease risk.
"These analyses provide new evidence supporting a cause-and-effect relation between lean mass and risk of Alzheimer's disease," said the researchers. 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," they added.
But the scientists 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.” Nor is it clear whether increasing lean mass could reverse the pathology of Alzheimer's disease in patients with preclinical disease or mild cognitive impairment, they added. But 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.”