Pregnant women who are low in the "sunshine vitamin" D may have an increased risk of a range of health problems, researchers warn today.
Gestational diabetes, pre-eclampsia, and small for gestational babies have all been linked to the problem.
The vitamin is generated in the body by exposure to sunshine – and people in countries with low sunshine levels are known to be at risk of having low levels.
Dr Doreen Rabi and colleagues at the University of Calgary in Canada looked at the impact on pregnancy and birth.
They analysed 31 earlier studies on vitamin D levels in pregnancy. Results are published in the British Medical Journal. Insufficient levels were associated with a 49% increased risk of gestational diabetes, say the authors. The risk of pre-eclampsia was raised by 79% and small for gestational age infants by 85%. It did not appear to be linked to length or head circumference at birth.
It also increased the chance of low birthweight and bacterial vaginosis (which itself raises the risk of preterm birth and low birthweight), but not delivery by caesarean.
The authors write: "These findings are of concern, particularly given recent evidence suggesting that 25-OHD deficiency or insufficiency is common during pregnancy, especially among high risk groups, including vegetarians, women with limited sun exposure (for example, those who live in cold climates or in northern latitudes, wear sun screen, or wear protective clothing), and those from ethnic minority groups with darker skin."
They add: "Vitamin D supplementation may be a simple way to reduce the risk of these adverse outcomes."
Commenting on the results, Dr Robyn Lucas of the Australian National University and colleagues agree that large, well-designed trials are needed "to clarify the causal association between vitamin D supplementation and health" and to understand "the potentially lifelong effects on the health of offspring".
Aghajafari, F. et al. Association between maternal serum 25-hydroxyvitamin D level and pregnancy and neonatal outcomes: systematic review and meta-analysis of observational studies. BMJ 27 March 2013 doi: 10.1136/bmj.f1169 [abstract]
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