Vitamin D supplements are incredibly popular, but whether vitamin D supplements should be taken during pregnancy and at what dose is still debated, and studies have had conflicting results. Now a review by Canadian researchers of 43 studies of vitamin D supplementation during pregnancy found that there is "insufficient evidence to guide recommendations during pregnancy". They said that overall the studies were small or of low quality - and the "available data did not provide evidence of benefit" from vitamin D supplementation during pregnancy.
They found that vitamin D supplementation slightly increased the mean (average) birth weight by 2 ounces (58.33 g), reduced the risk of small for gestational age births, and reduced the risk of the child wheezing at age 3. There was no effect on preterm birth, and there was a lack of evidence of benefits of prenatal vitamin D supplementation for maternal health conditions (e.g. gestational diabetes) during pregnancy.
Currently recommendations regarding vitamin D supplementation vary widely among medical and professional organizations, and WHO (World Health Organization) currently recommends against routine prenatal vitamin D supplementation. Luckily there are a number of studies going on right now on this issue that may help answer this question - how much vitamin D, if any, should be taken during pregnancy? From Medical Xpress:
There is currently insufficient evidence to guide recommendations on the use of vitamin D supplements in pregnancy, conclude researchers in The BMJ today. A team led by Dr Daniel Roth at The Hospital for Sick Children in Toronto, say some of the most critical questions about the effectiveness of taking vitamin D supplements during pregnancy "will probably remain unanswered in the foreseeable future."
Vitamin D helps maintain calcium levels in the body to keep bones, teeth and muscles healthy. Numerous studies suggest that taking vitamin D supplements may also help protect against heart disease, cancer, respiratory infections and asthma - as well as conditions related to pregnancy, such as preeclampsia and gestational diabetes. But results are conflicting and recommendations vary widely among medical and professional organisations.
So Dr Roth and his team set out to assess the current and future state of the evidence on vitamin D supplements during pregnancy. They analysed results from 43 randomised controlled trials involving 8,406 women, to estimate the effects of taking vitamin D supplements during pregnancy on 11 maternal and 27 child outcomes.... The results show that taking supplements during pregnancy increased vitamin D levels in both the mother's bloodstream and umbilical cord blood, but the researchers did not consistently find that higher doses of vitamin D led to healthier women and babies.
Overall, vitamin D increased average birth weight by 58 g and reduced the risk of having a small baby, but more detailed analyses weakened the authors' confidence in these findings. There was a lack of evidence of benefits of vitamin D supplements for maternal health conditions related to pregnancy, no effect on other birth outcomes of public health importance, such as premature birth, and scant evidence on safety outcomes. [Original study.]