Maternal obesity and baseline vitamin D insufficiency alter the response to vitamin D supplementation: a double-blind, randomized trial in pregnant women

Background: The achievement of target 25-hydroxyvitamin D [25(OH)D] concentrations in pregnancy may be altered by maternal obesity. Objective: The authors examined the effects of maternal supplementation of 10 mu g compared with 20 mu s vitamin D-3/d on maternal and umbilical cord 25(OH)D. The secondary aim was to investigate the influence of maternal BMI (in kg/m(2)) on the response of the primary outcomes. Methods: The authors performed a 2-arm parallel double-blind randomized trial with 240 pregnant women recruited throughout the year in Northern Ireland. Women were stratified by BMI to receive 10 or 20 mu g vitamin D-3/d from 12 gestational wk (GW) until delivery. Maternal blood samples collected at 12, 28, and 36 GW and from the umbilical cord were analyzed for total serum 25(OH)D. A total of 166 women completed the study. Results: Mean +/- SD 25(OH)D at 36 GW was 80.8 +/- 28.2 compared with 94.4 +/- 33.2 mnol/L . (P < 0.001) (10 compared with 20 mu g vitamin D-3/d, respectively). In those classified with 25(OH)D <50 nmol/L at baseline and assigned 10 mu g vitamin D-3/d. mean 25(OH)D concentrations remained <50 nmol/L at 36 GW, whereas those <50 nmol/L at base-line and assigned 20 mu g vitamin D-3/d, had mean 25(OH)D concentrations >50 nmol/L at 28 and 36 GW. In women with obesity and 25(OH)D <50 nmol/L at baseline, the related mean umbilical cord 25(OH)D was deficient (<25 nmol/L) in both treatment groups. whereas those with obesity and 25(OH)D >= 50 nmol/L at baseline had an average umbilical cord 25(OH)D between 25 and 50 nmol/L in both treatment groups. Conclusions: Supplementation of 20 mu g vitamin D-3/d is needed to attain maternal and umbilical cord 25(OH)D concentrations >= 50 nmol/L on average, in those who start pregnancy with low 2.5(OH)I) concentrations ( <50 nmol/L). Under current recommendations, women with obesity and low 25(OH)D in early pregnancy are particularly vulnerable to maintaining a low 25(OH)D concentration throughout pregnancy and having an infant born with deficient 25(OH)D concentrations.

Automated summary

Maternal supplementation of 20 μg vitamin D-3/d is more effective in achieving target 25(OH)D concentrations in pregnancy compared to 10 μg, especially for obese women. Low maternal 25(OH)D concentrations at baseline may lead to deficiencies in umbilical cord 25(OH)D, highlighting the importance of adequate vitamin D supplementation during pregnancy, especially for obese women.