Effect of muscle mass decrease on age-related BMR changes

The long known and often studied decrease in basal metabolic rate (BMR) with age was recently shown related to changes in the proportion of lean-to-fat tissue mass in the body. Earlier studies from this laboratory showed the decline in basal 0, consumption (basal 00,) to be accounted for by a decline in lean body mass (LBM). The purpose of the present study was to identify and account for that component of the lean body responsible for the age-related decrease in basal vo, in 959 participants in the Baltimore Longitudinal Study aged from 20 to 97 yr, An age-independent linear relation was found between paired values of basal voz, a measure of total metabolic activity, and 24-h creatinine excretion, a measure proportional to skeletal muscle mass. The relation is quanti-fied by basal Tie, = 99.1 + 0.079 (creatinine excretion), where basal vo, is expressed in mllmin (STPD) and creatinine excre-