Evaluation of vitamin D 3 metabolites in Callithrix jacchus (common marmoset)

Vitamin D 3 (cholecalciferol) is endogenously produced in the skin of primates when exposed to the appropriate wavelengths of ultraviolet light (UV‐B). Common marmosets ( Callithrix jacchus ) maintained indoors require dietary provision of vitamin D 3 due to lack of sunlight exposure. The minimum dietary vitamin D 3 requirement and the maximum amount of vitamin D 3 that can be metabolized by marmosets is unknown. Observations of metabolic bone disease and gastrointestinal malabsorption have led to wide variation in dietary vitamin D 3 provision amongst research institutions, with resulting variation in circulating 25‐hydroxyvitamin D 3 (25(OH)D 3 ), the accepted marker for vitamin D sufficiency/deficiency. Multiple studies have reported serum 25(OH)D 3 in captive marmosets, but 25(OH)D 3 is not the final product of vitamin D 3 metabolism. In addition to serum 25(OH)D 3, we measured the most physiologically active metabolite, 1,25‐dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ), and the less well understood metabolite, 24,25‐dihydroxyvitamin D 3 (24,25(OH) 2 D 3 ) to characterize the marmoset's ability to metabolize dietary vitamin D 3 . We present vitamin D 3 metabolite and related serum chemistry value colony reference ranges in marmosets provided diets with 26,367 (Colony A, N  = 113) or 8,888 (Colony B, N  = 52) international units (IU) of dietary vitamin D 3 per kilogram of dry matter. Colony A marmosets had higher serum 25(OH)D 3 (426 ng/ml [ SD 200] vs. 215 ng/ml [ SD 113]) and 24,25(OH) 2 D 3 (53 ng/ml [ SD 35] vs. 7 ng/ml [ SD 5]). There was no difference in serum 1,25(OH) 2 D 3 between the colonies. Serum 1,25(OH) 2 D 3 increased and 25(OH)D 3 decreased with age, but the effect was weak. Marmosets tightly regulate metabolism of dietary vitamin D 3 into the active metabolite 1,25(OH) 2 D 3 ; excess 25(OH)D 3 is metabolized into 24,25(OH) 2 D 3 . This ability explains the tolerance of high levels of dietary vitamin D 3 by marmosets, however, our data suggest that these high dietary levels are not required.