Pregnant women 'must take vitamin D supplements'
Pregnant women in the UK should be told to routinely take vitamin D supplements, researchers say.
The team at University College London Institute of Child Health says official bodies currently offer conflicting advice.
Writing in the British Journal of Nutrition, they say there is a "strong case" for a daily dose of vitamin D in pregnancy.
But one leading expert said more evidence was needed.
The Department of Health advises pregnant women to ensure they receive a certain level of vitamin D - 10 micrograms per day. The researchers say this in effect endorses use of supplements, because diet and the sun provide too little.
But the National Institute of health and Clinical Excellence (NICE) said in its guidance that it did not support supplements.
It has instead said that women should simply "be informed" about the importance of having adequate vitamin D levels during their pregnancy and while breastfeeding - adding that some women may choose to do this via supplements.
Additionally, pregnant women on low incomes are entitled to a range of nutrients - including vitamin D - as part of the Healthy Start Scheme.
The paper said the UK was the only one of 31 countries examined which did not recommend that women of reproductive age took a vitamin D supplement, and that it also fails to endorse a daily supplement for expectant mothers.
Dr Elina Hypponen, co-author of the paper, said: "The incidence of vitamin D deficiency in pregnant women in Britain is unacceptably high, especially during winter and spring.
"This is compounded by a lack of exposure to sunlight and the limitations of an average diet to meet the optimal need.
"In the most severe cases, maternal vitamin D deficiency can be life threatening to a newborn.
"We believe that the routine provision of a daily supplement throughout pregnancy would significantly decrease the number of mothers who are clearly vitamin D deficient, reducing related serious risks to their babies."
Dr Hypponen said past evidence showed a proactive approach to supplements coincided with a much lower incidence of deficiency linked diseases such as infantile hypocalcaemia [also known as William's syndrome, which affects development], and rickets [which weakens bones].
One in four
The authors say women from some ethnic minorities are recognised to be at greater risk because their darker skin means they do not absorb as much sunlight.
But they add that the problem is also common among white women, even when they live in southern England.
Women are more likely to be vitamin D deficient than men, and a previous study found one in four pregnant mothers has been found to be vitamin D deficient during winter and spring
The Royal College of Obstetricians and Gynaecologists recommends only women at risk of vitamin D deficiency should take a supplement.
Patrick O'Brien, a spokesman for the college, said: "There is gradually accumulating evidence that universal vitamin D supplementation in the UK might be beneficial for the whole population.
"But more research is needed on the balance of risks and benefits in women at low risk of vitamin D deficiency, and on the correct dosage to use."