Energy Restriction Does Not Alter Bone Mineral Metabolism or Reproductive Cycling and Hormones in Female Rhesus Monkeys

Energy restriction (ER) extends the life span and slows aging and age-related diseases in short-lived mammalian species. Although a wide variety of physiological systems have been studied using this paradigm, little is known regarding the effects of ER on skeletal health and reproductive aging. Studies in rhesus monkeys have reported that ER delays sexual and skeletal maturation in young male monkeys and reduces bone mass in adult males. No studies have examined the chronic effects on bone health and reproductive aging in female rhesus monkeys. The present cross-sectional study examined the effects of chronic (6 y) ER on skeletal and reproductive indices in 40 premenopausal and perimenopausal (7–27 y old) female rhesus macaques (Macaca mulatta). Although ER monkeys weighed less and had lower fat mass, ER did not alter bone mineral density, bone mineral content, osteocalcin, 25-hydroxyvitamin D, 1,25-hydroxyvitamin D or parathyroid hormone concentrations, menstrual cycling or reproductive hormone concentrations. Body weight and lean mass were significantly related to bone mineral density and bone mineral content at all skeletal sites (total body, lumbar spine, mid and distal radius; P ≤ 0.04). The number of total menstrual cycles over 2 y, as well as the percentage of normal-length cycles (24–31 d), was lower in older than in younger monkeys (P ≤ 0.05). Older monkeys also had lower estradiol (P = 0.02) and higher follicle-stimulating hormone (P = 0.02) concentrations than did younger monkeys. We conclude that ER does not negatively affect these indices of skeletal or reproductive health and does not alter age-associated changes in the same variables.