FAN XIANG*, ROBYN M LUCAS

*Corresponding author

National Centre for Epidemiology and Population Health,
The Australian National University, Canberra, Australia 0200

Abstract

Pregnancy is a state of increased vitamin D requirements to support fetal development. Vitamin D deficiency is common in pregnant women and has been linked to a wide range of adverse maternal and fetal outcomes.
Many epidemiological studies have examined vitamin D status during pregnancy in relation to the health of the mother and baby, but have used study designs where reverse causality may account for the link to disease. Stronger study designs, or meta-analyses of such studies, provide inconsistent results, although very low vitamin D levels are likely to be adverse. Intrauterine exposures can have long-lasting effects into adulthood, so that, while vitamin D deficiency during pregnancy should be avoided, supplementation to high levels may not be beneficial in either the short or long term.

The last 10 years have seen a rapid increase in interest in the possible health benefits of vitamin D – and the risks of vitamin D deficiency. To-date much of the evidence has derived from studies using geographic location, season, or levels of ambient ultraviolet radiation (UVR) as proxies for vitamin D status, or observational study designs, such as case-control or cohort studies. In case-control studies the vitamin D status of people with the disease is compared to those without the disease, i.e. disease has already occurred when blood sampling is undertaken. In cohort studies, blood is taken well before disease onset, and those with low blood levels are compared to those with higher levels, for the occurrence of the health outcome. To-date, there are few randomized controlled studies (RCTs) involving vitamin D supplementation, with comparison of outcomes between those who receive active supplements and those who do not. RCTs, and meta-analyses of the results of these studies, are recognized as providing the highest level of evidence of a causal association.

Several papers have provided narrative reviews of the possible risks of vitamin D deficiency during pregnancy ...