Mechanisms of changes in basal metabolism during ageing

A considerable number of physiological functions are known to show a gradua l decline with increasing age. However, the effects of ageing differ widely between organ systems. It is believed that basal metabolic rate (BMR) fall s dramatically with age. These observations, largely based on cross-section al surveys, are discussed in light of our present understanding of the biol ogy of ageing. This paper reviews both the longitudinal and cross-sectional studies of BMR and presents evidence that the fall in BMR with ageing may be less dramatic than previously perceived. Indeed, some subjects may show an increase in BMR with ageing. The mechanism of changes in BMR during agei ng will be discussed. Organ weight changes appear to have a profound impact on BMR. The use of BMR to predict total energy expenditure in the 'old eld erly' ( > 75 y) is unlikely to be of any practical use due to wide intra- a nd inter-individual variation in BMR. This wide intra- and inter-individual variation in BMR is due to illness, disease and other metabolic disorders seen in the elderly. Finally, the importance of measuring BMR in elderly po pulations for its use in clinical medicine will be discussed.