Serum Vitamin D Concentrations in Baboons (Papio spp.) during Pregnancy and Obesity

Obesity is associated with vitamin D deficiency, which can lead to serious problems during pregnancy. However, the mechanisms of the deficiency and guidelines for vitamin D supplementation during pregnancy are not established yet, and variations in environmental exposures combined with the difficulties of performing research in pregnant women are obstacles in the evaluation of vitamin D metabolism. Baboons (Papio spp.) are an excellent, well-established model for reproductive research and represent a unique opportunity to study vitamin D metabolism in a controlled environment. This study used secondary data and specimen analysis as well as a novel experimental design to evaluate pregnant and nonpregnant baboons that were or were not exposed to sunlight while they were obese and after weight reduction. Daily D₃ intake was 71% higher in nonpregnant obese baboons than in their nonobese counterparts, but serum vitamin D concentrations did not differ between these populations. In addition, serum 25-hydroxyvitamin D concentrations correlated negatively with the obesity index. This report is the first to show the effect of obesity and pregnancy on vitamin D concentrations in a NHP population. These data underline the importance of adequate vitamin D supplementation in obese animals.Vitamin D deficiency during pregnancy is a major public health problem³⁰ that is associated with increased maternal and neonatal morbidity.^5,6,22,31 Even though vitamin D is actively involved in placental function and fetal growth,^5,11,43 the dosage of vitamin D supplementation during pregnancy has not been established.³⁰ Maternal serum concentrations of 25-hydroxyvitamin D are directly related to vitamin D intake and sunlight exposure in humans.²⁷ Obesity is an important risk factor for vitamin D deficiency for which the mechanisms remain unknown, and the effect of weight loss on vitamin D status is unclear.^14,15,33,34 In addition, obesity itself is a significant public health problem.^18,51 Several mechanisms linking obesity and vitamin D deficiency have suggested, including decreased exposure to sunlight, sequestration of vitamin D in the adipose tissue,⁵⁰ and other factors related to obesity.^34,49 In pregnancy an additional factor involved in vitamin D activation and metabolism is the placenta^46-48—a temporary endocrine organ whose function is linked to the metabolism of the adipose tissue.⁷An understanding of the relationship between vitamin D, obesity, and pregnancy is critical for reducing maternal and neonatal morbidity. Baboons (Papio spp.) have been used extensively in pregnancy-related research.^17,40 The advantages of this model include the similarity of its placentation to that in humans and the ability to create uniform exposures to environmental factors (for example, sunlight, dietary composition) and thus study underlying metabolic pathways, which are impossible to study in the heterogeneous human population. However, only a very few studies related to the vitamin D requirements in these NHP species are available,^35,39 and none of them addresses the effect of obesity and pregnancy on vitamin D metabolism. The objective of the current study was to evaluate the effects of obesity, weight reduction, and pregnancy on the systemic vitamin D status of baboons, by using data collected during prior studies as well as a novel study design.