Resting (or basal) metabolic rate has been shown to broadly correlate with mammalian species life span, in that species with short life spans tend to have high metabolic rates, and species with long life spans tend to have low metabolic rates. It also tends to be the case that large mammals live longer than short mammals, with lower metabolic rates. Great longevity in primates when compared to other similarly sized mammals may have required a reduction in metabolic rate to have evolved. Species that do not follow this trend tend to be of interest to researchers investigating the comparative biology of aging. Some species of bats are small, long-lived, and exhibit very high metabolic rates. The long-lived naked mole-rat is metabolically unusual in any number of ways, including metabolic rate.
Do differences in resting metabolic rate between individuals in the same species predict life expectancy, however? There is evidence for this to be the case in humans. Resting metabolic rate does decline with age, and there have been efforts to use that decline as a biomarker of aging. Higher resting metabolic rate correlates with a shorter life expectancy and increased risk of age-related disease, however. We might argue that this has something to do with the level of activity undertaken by damaged cells in damaged tissues, and its influence on cancer risk. We might also argue that this has to do with the activity of the immune system, and the burden of infectious disease. Historically, human body temperature has declined over the period for which good records exist. Body temperature is a crude proxy for resting metabolic rate, and the burden of infectious disease has declined dramatically over this same period of time.
Metabolism has long been linked to the process of aging and longevity but the evidence from studies of their associations is not always in accordance. Total daily energy expenditure consists of basal metabolic rate (BMR), thermic effects of food, and energy expenditure from physical activity. BMR reflects the daily energy requirement for maintaining basic bodily functions. It is the major source of energy expenditure and is an important parameter for estimating daily energy requirements.
Observationally, the association of BMR with mortality is mixed, although some ageing theories suggest that higher BMR should reduce lifespan. It remains unclear whether a causal association exists. In this one-sample Mendelian randomization study, we aimed to estimate the casual effect of BMR on parental attained age, a proxy for lifespan, using two-sample Mendelian randomization methods. We obtained genetic variants strongly and independently predicting BMR from the UK Biobank and applied them to a genome-wide association study of parental attained age based on the UK Biobank.
A total of 178 and 180 genetic variants predicting BMR in men and women were available for father's and mother's attained age, respectively. Genetically predicted BMR was inversely associated with father's and mother's attained age (years of life lost per unit increase in effect size of genetically predicted BMR, 0.46 and 1.36), with a stronger association in women than men. In conclusion, higher BMR might reduce lifespan. The underlying pathways linking to major causes of death and relevant interventions warrant further investigation.