High basal metabolic rate is a risk factor for mortality: The Baltimore Longitudinal Study of Aging

Background. Despite longstanding controversies from animal studies on the relationship between basal metabolic rate (BMR) and longevity, whether BMR is a risk factor for mortality has never been tested in humans. We evaluate the longitudinal changes in BMR and the relationship between BMR and mortality in the Baltimore Longitudinal Study of Aging (BLSA) participants. Methods. BMR and medical information were collected at the study entry and approximately every 2 years in 1227 participants (972 men) over a 40-year follow-up. BMR, expressed as kcal/m(2)/h, was estimated from the basal O-2 consumption and CO2 production measured by open-circuit method. Data on all-cause and specific-cause mortality were also obtained. Result. BMR declined with age at a rate that accelerated at older ages. Independent of age. participants who died had a higher BMR compared to those who survived. BMR was a significant risk factor for mortality independent of secular trends in mortality and other well-recognized risk factors for mortality, such as age, body mass index, smoking, white blood cell count, and diabetes. BMR was nonlinearly associated with mortality. The lowest mortality rate was found in the BMR range 31.3-33.9 kcal/m(2)/h. Participants with BMR in the range 33.9-36.4 kcal/m(2)/h and above the threshold of 36.4 kcal/m(2)/h experienced 28% (hazard ratio: 1.28; 95% confidence interval, 1.02-1.61) and 53% (hazard ratio: 1.53; 95% confidence interval, 1.19-1.96) higher mortality risk compared to participants with BMR 31.3-33.9 kcal/m2/h. Conclusion. We confirm previous findings of an age-related decline of BMR. In our study, a blunted age-related decline in BMR was associated with higher mortality, suggesting that such condition reflects poor health status.