The research is the largest ever observational study of the effects of mothers' vitamin D levels in pregnancy on their children's bone health, and suggests that UK health guidelines may be overstating the importance of vitamin D supplementation in pregnancy.
3,960 pregnant women
The study, led by Professor Debbie Lawlor of the University of Bristol, assessed vitamin D levels in 3,960 pregnant women, recording data from all three trimesters. When their children had reached an average age of nine years and 11 months, their bone mineral content (BMC) was assessed using dual-energy X-ray absorptiometry. 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.
Vitamin D helps to keep a person's bones and teeth healthy by regulating the amount of calcium and phosphate in the body, and it has been thought that, as well as affecting maternal bone health, low levels of vitamin D during pregnancy might lead to problems with the baby's bone formation. Aside from dietary sources of vitamin D, which include oily fish, eggs, and meat, vitamin D is produced naturally in the body by the action of sunlight on skin.
However, in recent years, concerns have been raised over the possible adverse effects of low levels of vitamin D in pregnancy, leading National Institute for Health and Clinical Excellence guidelines to recommend in 2008 that all pregnant and breastfeeding women should take a 10 microgram vitamin D supplement every day.
Professor Lawlor now suggests that the guidelines may be "over-emphasising the importance of vitamin D."
The study, which was published in The Lancet, is part of the Avon Longitudinal Study of Parents and Children also known as Children of the 90s, a long-term health research project in which more than 14,000 mothers enrolled during pregnancy in 1991 and 1992.