How Important Is Vitamin D for Calcium Homeostasis During Pregnancy and Lactation?

Evaluating Vitamin D Status in Infants Less than Seven Months; What Are the Preferred Biochemical Measurements?

Background: To ensure the safety of higher dose vitamin D supplementation in pregnant and lactating mothers, and urinary calcium/creatinine (UCa/Cr) ratios, serum calcium, and serum 25(OH)D concentrations are closely monitored. To achieve optimal maternal and infant vitamin D status, while avoiding hypercalcemia, safety measures assessing vitD supplementation must be reliable. Whether or not this holds true for infants before 7 months of age, remains unknown. Objective: Analyze the association among UCa/Cr ratio, serum calcium, intact serum parathyroid hormone (iPTH), 25(OH)D, and 25(OH)D/iPTH ratio in infants to determine whether evidence supports the use of these parameters as valuable measures of hypervitaminosis D or toxicity in infants. Methods: A series of analyses were performed on the cohort of infants who participated in the National Institute of Child Health and Human Development lactation vitD supplementation trial to determine the association among UCa/Cr ratio, serum calcium, iPTH, 25(OH)D, and 25(OH)D/iPTH ratio. Results: Upon multivariate analysis, serum calcium was significantly associated with 25(OH)D (p = 0.0441), iPTH (p = 0.0017), and 25(OH)D/iPTH ratio (p = 0.0001). Infant UCa/Cr did not associate with 25(OH)D but did associate with iPTH (p = 0.0008) and 25(OH)D/iPTH ratio (p = 0.0001). The correlation between UCa/Cr and 25(OH)D/iPTH ratios was significantly stronger than the association between UCa/Cr ratio and iPTH. Serum calcium more strongly correlated with 25(OH)D/iPTH ratio versus 25(OH)D and iPTH. Conclusion: In this healthy cohort of infants 1 to 7 months old, UCa/Cr and serum calcium are more valid indicators of 25(OH)D/iPTH ratio than either 25(OH)D or iPTH alone. Moreover, serum calcium (and not UCa/Cr) is a valid indicator of infant total circulating 25(OH)D and should be measured if vitamin D toxicity is a concern. Clinical Trial Registration number: FDA IND Number: 66,346; ClinicalTrials.gov Number: NCT00412074.

The Role of Vitamin D in Fertility and during Pregnancy and Lactation: A Review of Clinical Data

Vitamin D deficiency is common and there exists a huge gap between recommended dietary vitamin D intakes and the poor vitamin D supply in the general population. While vitamin D is important for musculoskeletal health, there are accumulating data suggesting that vitamin D may also be important for fertility, pregnancy outcomes and lactation. Significant changes in vitamin D metabolism during pregnancy such as increased production of the “active vitamin D hormone” calcitriol support the important role of vitamin D in this setting. Observational studies show that vitamin D deficiency is a risk marker for reduced fertility and various adverse pregnancy outcomes and is associated with a low vitamin D content of breast milk. Meta-analyses of randomized controlled trials (RCTs) document that physiological vitamin D supplementation during pregnancy is safe and improves vitamin D and calcium status, thereby protecting skeletal health. Although certain RCTs and/or meta-analyses reported some other beneficial effects, it is still not clear whether vitamin D supplementation improves fertility or decreases the risk of adverse pregnancy outcomes such as low birth weight, pre-eclampsia and neonatal mortality, or reduces wheeze/asthma in the infants. Nevertheless, vitamin D supplementation in pregnant women is frequently required to achieve a sufficient vitamin D status as recommended by nutritional vitamin D guidelines. In this review, we provide an overview of systematic reviews, meta-analyses and large trials reporting clinical data on the role of vitamin D for fertility, pregnancy and lactation.