Vitamin D status in wild toque macaques (Macaca sinica) in Sri Lanka

The vitamin D receptor is found on most cells, including active immune cells, implying that vitamin D has important biological functions beyond calcium metabolism and bone health. Although captive primates should be given a dietary source of vitamin D, under free-living conditions vitamin D is not a required nutrient, but rather is produced in skin when exposed to UV-B light. The circulating level of 25 hydroxyvitamin D (25-OH-D) considered adequate for humans is a topic of current controversy. Levels of circulating 25-OH-D sufficient for good health for macaques and other Old World anthropoids are assumed to be the same as human values, but data from free-living animals are scant. This study reports values for 25-OH-D and the active vitamin D metabolite, 1,25-dihydroxyvitamin D (1,25[OH]₂ D) for wild, forest-ranging toque macaques (Macaca sinica) in Sri Lanka. Plasma samples were obtained from eight adult males, seven juvenile males, six young nulliparous females, nine adult females not pregnant or lactating, eleven lactating adult females, and four pregnant females. Mean values for the complete sample were 61.3 ± 4.0 ng/ml for 25-OH-D and 155.6 ± 8.7 pg/ml for 1,25[OH]₂ D. There were no significant differences for either metabolite among age and sex classes, nor between lactating and non-reproductive females. Values from the literature for circulating 25-OH-D in captive macaques are three times higher than those found in this wild population, however, 1,25[OH]₂ D values in captive animals were similar to the wild values. The data from this study indicate that anthropoid primates exposed to extensive sunlight will have circulating values of 25-OH-D generally above 30 ng/ml, providing some support for the Endocrine Society recommendations for humans. Current dietary vitamin D supplementation of captive macaques likely exceeds requirement. This may affect metabolism and immune function, with possible consequences for macaque health and biomedical research results.