Pregnancy health centre

Vitamin D in pregnancy 'does not affect children's bone health'

19th March 2013 - Official advice that mums-to-be should take a vitamin D supplement to protect their child's bone health may be unnecessary, according to a new study.

Researchers at the University of Bristol found that maternal levels of vitamin D during pregnancy are not associated with the bone health of children later in life.

However, some experts say that more research is needed before any firm conclusions can be drawn.

The research appears in the online edition of The Lancet.

Recommended supplement

Vitamin D is important for healthy bones and teeth, and it has been thought that as well as affecting the bone health of pregnant women, low levels of vitamin D during pregnancy might lead to problems with the baby's bone development.

Vitamin D is found naturally in foods such as oily fish, eggs and meat, but the NHS recommends that pregnant women should take a 10 microgram supplement of vitamin D each day throughout pregnancy and while breastfeeding.

Three previous studies into the association between Vitamin D levels in pregnant women and bone health in children produced mixed results. All the studies were small, whereas the Bristol researchers say they were able to draw on data from ten times as many individuals as all the previous research combined.

Measuring bone mineral content

Using information from the Avon Longitudinal Study of Parents and Children (the Children of the 90s study), the team assessed vitamin D levels in 3,960 mainly white women throughout their pregnancies. When their children had reached an average age of 9.9 years, their bone mineral content was measured. Bone mineral content, or BMC, is a measure of bone health, where a lower mineral content is associated with poorer bone health and higher risk of diseases such as rickets.

The researchers found no significant association between a mother’s vitamin D levels and their child’s BMC.  

Mothers’ vitamin D levels were on average lowest during their first trimester, and then increased as the pregnancy progressed. As expected, levels were higher when measured during summer months (because vitamin D is produced naturally body by the action of sunlight on the skin) and lower when measured during winter months.

Furthermore, although non-white mothers and those who smoked during pregnancy tended to have lower vitamin D levels overall, this appeared to have no effect on their children’s bone health.

Challenging the recommendations

Speaking to Lancet TV, Professor Debbie Lawlor, who led the study, says that current guidelines may be "overemphasising the importance of vitamin D", adding that more evidence is needed. She continues that "suggesting to pregnant women their child's future bone health depends on their pregnancy vitamin D status, or by taking a supplement they will improve that ... I think our study challenges that".