Vitamin D supplementation should be routine in pregnancy: AGAINST: Proven benefits of vitamin D supplementation remain elusive.

Abstract

Obstetricians have an unfortunate track record of implementing interventions before they are properly evaluated—examples include thalidomide for pregnancy nausea, tocolytics to suppress preterm labour, and vitamins C and E for the prevention of pre-eclampsia. In 2012 the Chief Medical Officers of the UK (Vitamin D—advice on supplements for at risk groups) recommended that, ‘All pregnant and breastfeeding women should take a daily supplement containing 10 μg of vitamin D’. However, as recently as 2003 the National Collaborating Centre for Women's and Children's Health antenatal care guideline (p.42) had recommended that ‘There is insufficient evidence to evaluate the effectiveness of vitamin D in pregnancy. In the absence of evidence of benefit, vitamin D supplementation should not be offered routinely to pregnant women’. This was updated in 2008 (p.12) to ‘women may choose to take 10 μg of vitamin D per day’ and supplementation was only ‘advised’ in women in high-risk groups (essentially, those with pigmented skin, or who usually remain covered when outdoors, or who have a poor diet, or are obese). There have been claims for the benefits of vitamin D in almost every pathological condition, and yet proven benefits remain elusive (Harvey BMJ 2012;345:e4695). The US Institute of Medicine in 2010 (Dietary Reference Intakes for Calcium and Vitamin D) concluded that, ‘More targeted research should continue. Higher levels have not been shown to confer greater benefits, and in fact, they have been linked to other health problems, challenging the concept that “more is better”. There is emerging evidence that too much of these nutrients may be harmful’. The Committee on Obstetric Practice of the American College of Obstetricians and Gynecologists (Vitamin D: Screening and Supplementation During Pregnancy) stated in July 2011 that, ‘At this time there is insufficient evidence to support a recommendation for screening all pregnant women for vitamin D deficiency’ and suggested that ‘vitamin D supplementation during pregnancy beyond that contained in a prenatal vitamin should await the completion of ongoing randomized clinical trials’. A 2013 comment in the Lancet suggested that the safest approach was to recommend supplementation only in high risk women as defined by the National Institute of Health and Clinical Excellence (NICE) (Steer Lancet 2013;381:2143–5). The latest Health Technology Assessment review of vitamin D supplementation in pregnancy (Health Technol Assess 2014;18:1–190) has concluded that ‘It is not possible to make rigorously evidence-based recommendations regarding maternal vitamin D supplementation during pregnancy’ and added ‘Although modest doses of vitamin D in pregnancy might well be relatively safe, at least in the short term, there are no long-term data to inform their potential long-term effects on offspring health. As with most interventions, it is probably optimistic to expect that there will be no risk of adverse events’. Surely it is time that we learned to do the proper studies before making potentially harmful recommendations. Philip Steer is Emeritus Editor, BJOG. For a full disclosure of interests, please go to www.BJOG.org.