A randomised controlled trial of vitamin d supplementation in pregnancy — ASN Events
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A randomised controlled trial of vitamin d supplementation in pregnancy (#98)

Constance Yap 1 , Mark McLean 1 , Wah Cheung 1 , Jenny Gunton 1 2 , Neil Athayde 3 , Craig Munns 4
  1. Diabetes and Endocrinology, Westmead Hospital, Sydney, NSW, Australia
  2. Diabetes and Transcription Factors Group, Garvan Institute of Medical Research , Sydney, NSW, Australia
  3. Obstetrics and Gynaecology, Westmead Hospital, Sydney, NSW, Australia
  4. Institute of Endocrinology and Diabetes, The Children's Hospital at Westmead , Sydney, NSW, Australia

Aim: Vitamin D deficiency in pregnancy is associated with an increased risk of Gestational Diabetes in observational studies.1 2  We aimed to examine the effects of vitamin D supplementation in pregnancy on maternal glucose metabolism.

Method: We conducted a blinded randomised controlled trial of pregnant women attending antenatal care. Women were recruited in early pregnancy and were randomised to receive either standard recommended dose of vitamin D 400 IU/day or vitamin D 5000 IU/day. The primary outcome was glucose metabolism as measured by 75g glucose tolerance test (75g OGTT) performed between 26-28 weeks of pregnancy. Primary analysis was performed according to intention to treat principle using the t-test to compare mean plasma glucose levels between the standard and high dose supplement groups.

Results: One hundred and seventy-nine women were randomised, 90 to the 400 IU/day group and 89 to the 5000 IU/day group. There was no difference in baseline characteristics of age, parity, weight and body mass index, baseline 25-hydroxyvitamin D level (25OHD) or other biochemistry.

Of the 179 women, 13 women withdrew from the study, 2 women had miscarriages and 1 woman had a preterm delivery. One hundred and fifty nine women underwent the 75g OGTT at 26-28 weeks gestation. One woman did not complete her OGTT and was excluded from analysis. A total of 19 women developed gestational diabetes – 12 were from the 400 IU/day group and 7 were from the 5000 IU/day group. Mean 25OHD level was 59.8nmol/L in the 400 IU/day group and 89.6nmol/L in the 5000 IU/day group (p=0.05). Mean fasting plasma glucose in the 400 IU/day and 5000 IU/day groups were 4.14mmol/L and 4.16mmol/L (p=0.61) and mean 2-hr plasma glucose were 6.16mmol/L and 5.97mmol/L (p=0.54).

Conclusion: High dose vitamin D supplementation did not confer any meaningful benefit to glucose metabolism during pregnancy over standard dose vitamin D supplementation. 

  1. Zhang C et al. Maternal Plasma 25-Hydroxyvitamin D Concentrations and the Risk for Gestational Diabetes Mellitus. PLoS ONE. 2008;3(11)e3753
  2. Maghbooli Z et al. Correlation between vitamin D3 deficiency and insulin resistance in pregnancy. Diabetes Metab Res Rev 2008;24:27-32