AGE AND SEX-DIFFERENCES IN BODY-SIZE AND COMPOSITION DURING RHESUS-MONKEY ADULTHOOD

Body size and composition were measured in forty-one adult Rhesus monk eys (Macaca mulatta) in order to characterize changes that occur durin g later life for both genders. Data were obtained by traditional somat ometric techniques and by dual-energy X-ray absorptiometry. Representa tive monkeys were chosen within six categories defined by age (Young A dult, 6-9 year-old; Middle Aged, 15-19 year-old; Older Adult, 26-30 ye ar-old), and sex. Body weight and most external measures of body size were greater during middle age and later life than in young adulthood, as were body fat content and lean body mass. Females tended to have a higher percentage body fat than males in all age categories. Lean tis sue mass was markedly greater in the two younger groups for both sexes , compared to older adults. Bone mineral content and density were high er in the males than the females, but differences in bone mineralizati on among age groups did not achieve statistical significance. Such dat a derived from adult nonhuman primates are useful for defining fundame ntal biological changes with age in these species, and have value as a comparative model for studies of human aging and age-related morbidit y.