Skeletal effects of long-term caloric restriction in rhesus monkeys

Abstract

Age-related bone loss is well established in humans and is known to occur in nonhuman primates. There is little information, however, on the effect of dietary interventions, such as caloric restriction (CR), on age-related bone loss. This study examined the effects of long-term, moderate CR on skeletal parameters in rhesus monkeys. Thirty adult male rhesus monkeys were subjected to either a restricted (R, n = 15) or control (C, n = 15) diet for 20 years and examined throughout for body composition and biochemical markers of bone turnover. Total body, spine, and radius bone mass and density were assessed by dual-energy X-ray absorptiometry. Assessment of biochemical markers of bone turnover included circulating serum levels of osteocalcin, carboxyterminal telopeptide of type I collagen, cross-linked aminoterminal telopeptide of type I collagen, parathyroid hormone, and 25(OH)vitamin D. Overall, we found that bone mass and density declined over time with generally higher levels in C compared to R animals. Circulating serum markers of bone turnover were not different between C and R with nonsignficant diet-by-time interactions. We believe the lower bone mass in R animals reflects the smaller body size and not pathological osteopenia.

Fig. 1

Influence of CR on body weight. Points represent group means with standard errors for each time point. Closed diamonds and solid lines represent control (C) animals, and open squares and dashed lines represent restricted (R) animals. Diet-by-time interaction was significant (p < 0.001) with an increase (p < 0.001) in the C animals

Fig. 2

Influence of CR on DXA-measured total body fat (a) and lean (b) mass. Points represent group means with standard errors for each time point. Closed diamonds and solid lines represent control (C) animals, and open squares and dashed lines represent restricted (R) animals. For fat mass, diet-by-time interaction was significant (p < 0.0001) explained by an increase in the C group (a). For lean mass, diet-by-time interaction was significant (p < 0.0001) explained by a decrease in the C group (b)

Fig. 3

Influence of CR on DXA-measured total body BMD. Points represent group means with standard errors for each time point. Closed diamonds and solid lines represent control (C) animals, and open squares and dashed lines represent restricted (R) animals. For total body BMD, the diet (p < 0.0001) and time period (p < 0.0001) were significant. C animals have higher total body BMD than R animals, and it changes over time and declines with age

Fig. 4

Influence of CR on DXA-measured PA lumbar spine BMD. Points represent group means with standard errors for each time point. Closed diamonds and solid lines represent control (C) animals, and open squares and dashed lines represent Restricted (R) animals. Main effects of diet and time as well as diet-by-time interaction were not significant

Fig. 5

Influence of CR on DXA-measured lateral lumbar spine BMD. Points represent group means with standard errors for each time point. Closed diamonds and solid lines represent control (C) animals, and open squares and dashed lines represent restricted (R) animals. Main effects of diet and time were not significant, however, the diet-by-time interaction was statistically significant (p = 0.0140)

Fig. 6

Influence of CR on DXA-measured distal radius BMD. Points represent group means with standard errors for each time point. Closed diamonds and solid lines represent control (C) animals, and open squares and dashed lines represent restricted (R) animals. For distal radius BMD, both diet (p = 0.0340) and time (p = 0.0066) were significant factors

Fig. 7

Influence of CR on DXA-measured radius shaft BMD. Points represent group means with standard errors for each time point. Closed diamonds and solid lines represent control (C) animals, and open squares and dashed lines represent restricted (R) animals. C and R animals did not differ in radius shaft BMD; however, BMD significantly declined over time (p < 0.0001)