Prospective cohort study of vitamin D deficiency in pregnancy: Prevalence and limited effectiveness of 1000 IU vitamin D supplementation

Abstract

Background: Vitamin D deficiency is highly prevalent worldwide among pregnant women. Although vitamin D supplementation is effective in improving vitamin D status, the safety and optimal dosing of vitamin D supplementation during pregnancy remain less well understood. Objective: This study aimed to investigate the prevalence of vitamin D deficiency among pregnant women and evaluate the effectiveness of vitamin D supplementation in improving vitamin D status during pregnancy. Design: This prospective cohort study assessed the impact of a 16-week daily vitamin D supplementation 1000 IU regimen on vitamin D status among pregnant women. Methods: A total of 365 pregnant women were recruited, and their baseline total circulating 25-hydroxy vitamin D concentrations were measured. Of these, 249 participants completed the study, which involved oral daily supplementation with 1000 IU of vitamin D and a repeat of total circulating 25-hydroxy vitamin D concentrations after 16 weeks. Results: The study found that 57.7% of the participants had vitamin D deficiency, consistent with the rates reported in other studies. However, vitamin D supplementation at a dose of 1000 IU had a small effect size and was not clinically significant. However, 67% of participants with vitamin D deficiency remained deficient; among participants initially with vitamin D insufficiency, 30% became deficient. Moreover, 26.5% of individuals with sufficient vitamin D status at 12 weeks showed insufficient levels by 28 weeks. Conclusion: Vitamin D deficiency is widespread among pregnant women, and vitamin D supplementation at a daily dose of 1000 IU may not adequately address this problem. Although the study has limitations, its results align with previous research and may apply to other populations with a high prevalence of vitamin D deficiency during pregnancy. Further research is necessary to determine the most effective approach for addressing prenatal vitamin D deficiency.