Investigating the Effect of Vitamin D Supplementation on Maternal Serum ۲۵(OH)D Levels

Background & aim: Although evidence confirms the importance of vitamin D supplementation in pregnancy, there is still a debate over the adequate daily doses of vitamin D intake. This study aimed to investigate the effect of ۴۰۰ and ۱,۰۰۰ IU vitamin D/day on maternal serum ۲۵ (OH) D levels. Methods: This quasi-experimental study was carried out on ۷۴ healthy pregnant women between June ۱۲ and September ۲۲, ۲۰۱۹. The intervention group (n=۴۴) received ۱,۰۰۰ IU vitamin D/day from ۸ to ۱۰ weeks of pregnancy for ۱۷ weeks, while the control group (n=۳۹) took multivitamin supplements (۴۰۰ IU vitamin D/day) from ۱۶ weeks of pregnancy for ۱۲ weeks. Maternal serum ۲۵ (OH) D levels were measured at ۲۵-۲۸ weeks of gestation. Data were analyzed in SPSS software (version ۲۱) through the Chi-square, Student’s t-test, Mann-Whitney U, and linear regression tests.  Results: There was no significant difference between the two groups at the beginning of the study in terms of ۲۵ (OH) D concentration (P=۰.۲۳). The intake of ۱,۰۰۰ IU vitamin D/day had a significant (β=۰.۲۸, p <۰.۰۰۱), yet small effect (effect size=۰.۳۰), on increasing serum ۲۵ (OH) D levels after controlling the confounding variables. About half of the females who took ۱,۰۰۰ IU vitamin D/day had a serum ۲۵(OH) D level less than ۳۰ ng/dl at ۲۵-۲۸weeks of pregnancy. Conclusion: Even after receiving ۱,۰۰۰ IU/day Vitamin D, vitamin D insufficiency was still prevalent during the second trimester of pregnancy. It seems that a higher dosage of vitamin D is required for pregnant women. 

Keywords:

Vitamin D deficiency , pregnancy , ۲۵-hydroxyvitamin D