Metabolism is the conversion of energy from food into energy for life-sustaining tasks such as breathing, circulating blood, building and repairing cells, digesting food, and eliminating waste. For sedentary adults, basal metabolic rate (the metabolic rate at rest) accounts for about 50% to 70% of total energy output, dietary thermogenesis for 10% to 15%, and physical activity for the remaining 20% to 30%.
At approximately 60 years old, BMR begin to decline, along with fat mass. However, declines in energy expenditure exceed that expected from reduced body mass alone. This is similar that what is found in several neurodegenerative diseases, albeit at a much slower rate.
Numerous studies suggest that metabolic dysfunction increases the risk of Alzheimer's disease. For instance, impaired glucose metabolism in the brain has been linked to Alzheimer's disease and may start several years before the onset of clinical symptoms.
Due to the long incubation period between exposure and results, randomized controlled trials, the gold standard for causal reasoning, are not feasible. In addition causation and confounding often substantially impede or mislead the interpretation of results from epidemiological studies. So scientists use Mendelian randomization, which is a method for obtaining unbiased estimates of the effects of a putative causal variable without conducting a traditional randomized controlled trial.
In a new publication, scientists determined the causal relationship between BMR and Alzheimer's disease by two-way Mendelian randomization and investigated the impact of factors associated with BMR on Alzheimer's disease.
The authors searched for a possible causal relationship between Alzheimer's disease and factors related with BMR, hyperthyroidism and type 2 diabetes, height and weight.
BMR was found to have a causal relationship with Alzheimer's disease, but there was no causal relationship between hyperthyroidism or type 2 diabetes in one hand and Alzheimer's disease in the other hand.
The authors' study showed that higher BMR reduced the risk of Alzheimer's disease, and patients with Alzheimer's disease had a lower BMR.
A person may be able to change their BMR through regular cardiovascular exercise.