Vitamin D in pregnancy
“Women 'should take vitamin D in pregnancy to stave off rickets'” is the headline in The Daily Telegraph today. It suggests that vitamin D supplements may also benefit infants and toddlers. A US study found that “infants who were fed exclusively on breastmilk by mothers who did not take vitamin D supplements were more than 10 times as likely to show signs of a deficiency than bottle-fed babies”. The study found that exposure to the sun, sunscreen use, and skin colouring had no effect on vitamin D deficiency among babies and toddlers.
The newspaper story is based on a study that looked at vitamin D levels in the blood of infants and toddlers up to the age of two years. Current UK guidance from the National Institute for Health and Clinical Excellence (NICE) states that it is important to maintain adequate vitamin D during pregnancy and breastfeeding, and that women may choose to take up to 10 micrograms of vitamin D a day during these periods, particularly if they have specific risk factors for vitamin D deficiency. The NHS also provides vitamin supplements containing vitamin D for eligible children aged between six months and four years.
Where did the story come from?
Dr Catherine Gordon and colleagues from the Children’s Hospital in Boston, USA carried out this research. The study was funded by Allen Foundation Inc, the McCarthy Family Foundation, the National Center for Research Resources, and the Maternal and Child Health Bureau, US Health Resources and Services Administration. It was published in the peer-reviewed medical journal: Archives of Pediatric and Adolescent Medicine .
What kind of scientific study was this?
This was a cross-sectional study looking at how common vitamin D deficiency was, and what factors affected vitamin D levels in the blood. The researchers enrolled 380 healthy infants and toddlers aged between eight months and two years from an urban primary care clinic in Boston between 2005 and 2007. Children who had serious medical conditions or who had taken medication that would affect vitamin D levels were not included.
All eligible children had routine blood samples taken, and the researchers measured the levels of vitamin D and other substances. Levels of vitamin D of above 30 nanograms per millilitre (ng/ml) were considered ideal, and children with levels of 20 ng/ml or less were considered to have a vitamin D deficiency. Those with levels of 8 ng/ml or less were classified as having a severe deficiency. These levels were based on the general consensus among experts in the field about the ideal levels for vitamin D.
The researchers also collected information about the children: gender, height, weight, sun exposure, skin pigmentation and their parents’ health and other characteristics (sun exposure, race/ethnicity, education level, socioeconomic status). Children’s parents filled out a questionnaire about their diet and their child’s nutrition. This covered breastfeeding history for children younger than one year, plus milk, juice, fortified cereal and water consumption for older children. Parents also reported whether they used vitamin D supplements.
The researchers looked at whether any of the child or parents’ characteristics affected their likelihood of having vitamin D deficiency. When looking at the effect of each factor, they adjusted for the other factors. Children with vitamin D deficiency had X-rays of their wrists and knees to examined for evidence of rickets (graded on a standard 10-point scale) and to see whether the bones had lost some of their mineral content. X-rays were assessed by two independent radiologists.
What were the results of the study?
Of the 380 children enrolled, 365 had blood samples taken. Forty-four of the children (about 12%) had a vitamin D deficiency and seven (about 2%) had a severe vitamin D deficiency. Overall, 146 children (40%) had below the ideal level of vitamin D. Children’s gender, time spent outside, skin colour and sun sensitivity and sunscreen use did not affect their risk of vitamin D deficiency, nor did the season in which the measurement was taken.
Infants whose mothers breastfed them but who did not take any vitamin D supplements, were more likely to have vitamin D deficiency compared with those who were bottle fed. There was no difference between infants of breastfeeding mothers who took vitamin D supplements and those who exclusively bottle fed. Toddlers who drank less milk were also more likely to have a vitamin D deficiency than those who drank more milk. Thirteen of the children (about 33%) with vitamin D deficiency showed a loss of mineral in their bones on X-ray, and three children (about 8%) showed signs of rickets on X-ray. Only one child showed signs of rickets on physical examination.
What interpretations did the researchers draw from these results?
The researchers concluded that having lower than ideal vitamin D levels was common in young children who are otherwise healthy. About a third of children with vitamin D deficiency show a loss of bone. The factors that predict whether a child is at risk of vitamin D deficiency differ depending on the child’s age.
The author of the study, Dr Catherine Gordon, is quoted in the Telegraph saying: "These data underscore the fact that all breastfed infants should receive vitamin D supplementation for the duration of breastfeeding.”
What does the NHS Knowledge Service make of this study?
This was a well-conducted study of the prevalence of vitamin D deficiency in the blood of infants and toddlers. There are some points to consider when interpreting these results:
- Even though 40% of children aged under two years had levels of vitamin D that were considered less than ideal, they were all generally healthy. The study did not investigate what effects these reduced levels of vitamin D in early childhood would have on health at later ages.
- Only one blood sample was taken for each child, therefore these readings may not have been representative of their vitamin D levels over a period of time. Without information about vitamin D levels and bone density over a period of time, it is not possible to firmly conclude that vitamin D deficiency was responsible for the bone changes seen.
- The study sample included a high proportion of African Americans (about 61%) and a high proportion of non-breastfed infants. The results may not be representative of samples with different ethnic backgrounds or with a different proportion of breastfed infants.
Current UK guidance from NICE suggests that it is important to maintain adequate vitamin D during pregnancy and breastfeeding, and that women may choose to take up to 10 micrograms of vitamin D a day during these periods, particularly if they have specific risk factors for vitamin D deficiency. In the UK, the NHS provides vitamin supplements containing vitamin D for eligible children aged between six months and four years.
Sir Muir Gray adds...
This dose of vitamin D won’t do any harm; the evidence of benefit could be stronger, but when the balance of good to harm is so favourable it seems sensible to act.
