Vitamin D and mineral metabolism after childbirth with the use of preventive doses of cholecalciferol

Hypothesis/aims of study. According to the literature, the prevalence of vitamin D deficiency and its deficiency in pregnant women reaches 60–80%, which is a significant factor in reducing bone mineral density (BMD), osteopenia, and the risk of fractures after childbirth. Hormone-mediated changes in calcium-phosphorus metabolism during lactation are an independent factor in the reduction of BMD. Therefore, the study of the relationship between vitamin D deficiency and insufficiency after childbirth and the possibility of correction is relevant. The aim of this study was to evaluate the effect of prophylactic doses of cholecalciferol and calcium carbonate over time on calcium-phosphorus metabolism indicators after childbirth.

Study design, materials and methods. A randomized controlled trial was conducted based on V.A. Almazov National Medical Research Center, Saint Petersburg. 64 puerperas, who lived in St. Petersburg from 2013 to 2014, were surveyed on the 3–5^th day after childbirth. The age of women ranged from 20 to 35 years. Blood serum levels of calcium, phosphorus, magnesium, 25-hydroxycalciferol (25(OH)D), and parathyroid hormone (PTH) were determined for all the puerpera. Using the blind envelope method, the postpartum women were randomized into groups: group I received cholecalciferol 400 IU and calcium carbonate 1000 mg after delivery for 6 months; group II received cholecalciferol 900 IU and calcium carbonate 1000 mg after delivery for 6 months. Blood sampling was performed over time to assess the levels of 25(OH)D, PTH, calcium, phosphorus, and magnesium.

Results. In group I after childbirth, the initial level of 25(OH)D in the blood serum was 22.46 ± 4.35 ng/ml, which corresponds to vitamin D insufficiency. An increase in 25(OH)D level by 3.56 ng/ml was observed after 3 months from the start of taking cholecalciferol 400 IU. After 6 months, the level of 25(OH)D reached normal values in 20% of women (p = 0.0001). In group II after childbirth, the initial level of 25(OH)D in the blood serum was 20.64 ± 5.37 ng/ml, which corresponds to vitamin D insufficiency. An increase in 25(OH)D level by 7.60 ng/ml was observed after 3 months from the start of taking cholecalciferol 900 IU. After 6 months, the level of 25(OH)D reached normal values in 56% of women, while the average level of 25(OH)D in these women corresponded to its normally low values. The levels of PTH, calcium, phosphorus, and magnesium remained within the reference values in both groups; however, there was an increase in PTH concentration 6 months after delivery, which may indicate that the cholecalciferol dose is insufficient to stabilize PTH.

Conclusion. Vitamin D deficiency and insufficiency occurred in 80-97 % of those examined after delivery. The use of prophylactic doses of cholecalciferol has a positive effect on calcium-phosphorus metabolism; however, they are not sufficient to stabilize PTH level. The cholecalciferol dose of 400 IU is insufficient to normalize the level of 25(OH)D within 6 months of administration. The cholecalciferol dose of 900 IU leads to normally low values of 25(OH)D in 56 % of women after 6 months of administration, but this does not stabilize PTH level either.