Age and sex differences in body size and composition during rhesus monkey adulthood

Body size and composition were measured in forty-one adult Rhesus monkeys (Macaca mulatta) in order to characterize changes that occur during later life for both genders. Data were obtained by traditional somatometric techniques and by dual-energy X-ray absorptiometry. Representative monkeys were chosen within six categories defined by age (Young Adult, 6-9 year-old; Middle Aged, 15-19 year-old; Older Adult, 26-30 year-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 tissue mass was markedly greater in the two younger groups for both sexes, compared to older adults. Bone mineral content and density were higher in the males than the females, but differences in bone mineralization among age groups did not achieve statistical significance. Such data derived from adult nonhuman primates are useful for defining fundamental biological changes with age in these species, and have value as a comparative model for studies of human aging and age-related morbidity.