TITLE:
A Randomized Control Trial Comparing Vitamin D Supplementation versus Placebo on Glycemic Control in Gestational Diabetes Mellitus
AUTHORS:
Nanayakkara Kuruppuge Tharaka Sujeewe Sandaruwan, Yahampath Arachchige Gamini Perera, Carmoline Motha
KEYWORDS:
Gestational Diabetes, Vitamin D, Supplementation in Pregnancy, Pregnancy, Glycemic Control
JOURNAL NAME:
Open Journal of Obstetrics and Gynecology,
Vol.15 No.9,
September
25,
2025
ABSTRACT: Introduction: The definition of Gestational Diabetes (GD) is glucose intolerance of variable degree with onset or first recognition during pregnancy. Prevalence is 7% - 14% and high in South Asians. It is the most common metabolic disease in pregnancy and is associated with high maternal, fetal, and neonatal morbidity as well as mortality. Increased peripheral insulin resistance and impaired insulin secretion occur in affected individuals. Regulation of insulin secretion is influenced by hormones as well as circulating fuels like glucose. Recent studies have shown that there are other factors which play a role in insulin secretion, such as vitamin D. Objectives: This study was carried out to compare the efficacy of Vitamin D (oral) supplementation versus placebo on the control of blood sugar in gestational diabetes. Our hypothesis was that Vitamin D supplementation would increase insulin release and improve glycemic control in pregnant women with gestational diabetes. Monitoring for any adverse effects of vitamin D supplementation was also an objective. Methodology: This was a randomized, double-blind, placebo-controlled clinical trial. The study setting was the antenatal clinic of Colombo North Teaching Hospital, Ragama, Sri Lanka (a major obstetric unit in Sri Lanka) during the period of June 2018 to January 2019. Each arm contained 24 persons and the total sample size was 48. After excluding the subjects according to the exclusion criteria, the rest of the patients were recruited to the trial. The randomization was done by block randomization using web-based software and the sealed envelope method was used. For the intervention group, oral Vitamin D (Alfacalcidol-0.25 mg) was given once daily during the intervention for 4 weeks. A placebo was given to the control arm. FBS and 1h PPBS values were taken before entry into the study and after 4 weeks. The FBS and 1-hour PPBS levels in the two groups’ pre-intervention and post-intervention were compared. The results were analyzed by SPSS software using its standard statistical tools. Mothers and newborns were monitored for adverse outcomes until discharged from the hospital after delivery. Results: The mean age was 29y, the mean POA at entry was 26 weeks, and the mean BMI was 26 in the study group. The supplementation of oral vitamin D did not show any significant improvement in glycemic control, as measured by the change of FBS (p & lt; 0.26), and the change of 1h PPBS (p & lt; 0.17) in gestational diabetes. There were no adverse reactions found due to vitamin D supplementation during the antenatal period. There were no major congenital defects found in newborns. Conclusions and recommendations: Vitamin D supplementation in GD did not improve glycemic control (FBS or 1 h PPBS) significantly. No adverse reactions were observed among patients during vitamin D treatment. Vitamin D did not cause any major adverse effects to the fetus. There is an unmet need for RCTs in this area and large trials with a greater number of cases should be conducted. Future trials should address normal BMI, overweight patients, and obese patients separately in the supplementation of Vitamin D.