TORONTO – There is currently insufficient evidence to guide recommendations on the use of vitamin D supplements in pregnancy, conclude researchers in The BMJ on November 29, 2017.
A team led by Dr. Daniel Roth, a clinician-scientist in the Department of Paediatrics and the Centre for Global Child Health at The Hospital for Sick Children (SickKids), found there are still unanswered questions about effects of prenatal vitamin D supplementation on the health of pregnant women and their offspring.
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 organizations. For example, the World Health Organization does not advise healthy women to take vitamin D supplements during pregnancy.
Roth and his team set out to assess the current and future state of the evidence on vitamin D supplements during pregnancy.
They analyzed results from 43 randomized controlled trials involving 8,406 women, to estimate the effects of taking vitamin D supplements during pregnancy on 11 maternal and 27 child outcomes. Although differences in study design and quality were taken into account to minimize bias, they found substantial variation among trials.
“In our view, the evidence is not yet strong enough to support or guide specific recommendations for routine supplementation with vitamin D in pregnancy based on its effects on health outcomes,” says Roth, lead author of the study.
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 58g 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.
There was strong evidence that vitamin D reduced the risk of wheeze in offspring by 3 years of age. However, this finding was mainly based on just two of the 43 trials reviewed, and the authors say further work is needed before prenatal vitamin D can be recommended as a routine preventive measure against childhood asthma.
They point out that most trials were small (average sample size of 133 pregnant women) and many were conducted in ways that made them prone to bias. As such, they concluded that “there is currently insufficient evidence to guide prenatal vitamin supplementation recommendations.”
They also identified a further 35 trials registered as completed (but unpublished), ongoing or planned that the authors say may contribute 12,530 additional participants to future reviews.
“Cautious projections for the next decade suggest that we will eventually know more about vitamin D in pregnancy than we do now, but in the absence of a coordinated effort and funding to conduct large new trials, some of the most critical questions about the effectiveness of prenatal vitamin D supplementation will probably remain unanswered in the foreseeable future,” they conclude.
About The Hospital for Sick Children
The Hospital for Sick Children (SickKids) is recognized as one of the world’s foremost paediatric health-care institutions and is Canada’s leading centre dedicated to advancing children’s health through the integration of patient care, research and education. Founded in 1875 and affiliated with the University of Toronto, SickKids is one of Canada’s most research-intensive hospitals and has generated discoveries that have helped children globally. Its mission is to provide the best in complex and specialized child and family-centred care; pioneer scientific and clinical advancements; share expertise; foster an academic environment that nurtures health-care professionals; and champion an accessible, comprehensive and sustainable child health system. SickKids is proud of its vision for Healthier Children. A Better World.
About the SickKids Centre for Global Child Health
The Centre for Global Child Health is the dedicated hub for global child health-focused activities at The Hospital for Sick Children (SickKids). With a rich history of innovation in global paediatric health and a reputable network of global partners, the Centre for Global Child Health is well poised to effectively address global child health issues. The Centre supports the global health agenda through collaborative research grounded in scholarship, sustainable capacity building through education, advocacy for improved maternal and child health and the active communication of results to local, national and international stakeholders. For more information, please visit www.sickkids.ca/globalchildhealth and follow us on Twitter @SickKidsGlobal.
The Hospital for Sick Children (SickKids)