Published in The Lancet, the new data found no significant association between a mother's vitamin D levels and their child's bone mineral content (BMC). The UK-based researchers behind the study have now warned that health guidelines may be overstating the importance of vitamin D supplementation in pregnancy.
Led by Professor Debbie Lawlor of the University of Bristol, UK, the research team followed nearly 4,000 pregnant women to assess their vitamin D status and later outcomes for their children's bone health - finding no evidence of any association between maternal vitamin D concentrations - measured as 25(OH)D -in pregnancy and offspring total-body or spinal bone mineral concentrations.
"We believe that there is no strong evidence that pregnant women should receive vitamin D supplementation to prevent low BMC in their offspring, although we cannot comment on other possible effects of vitamin D in pregnant women," said Lawlor - who added that given the 'uncertain evidence' for the effects of maternal vitamin D on bone health, current health guidelines may be "over-emphasising the importance of vitamin D"
Remarking on the research in a comment piece for The Lancet, Professor Philip Steer from Imperial College London, UK, added that there have been inconsistencies in the results of previous studies, also seem to raise questions over why vitamin D supplementation is recommended for all pregnant and breastfeeding women.
"The safest approach is probably routinely to supplement pregnant women at greatest risk ... For other women, the optimum approach is unclear, and long-term randomised trials of supplementation are justified," he said.
Lawlor and her team assessed blood plasma vitamin D levels in 3960 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.
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 and lower when measured during winter months, said the team.
Furthermore, although non-white mothers and those who smoked during pregnancy tended to have lower vitamin D levels overall, however this appeared to have no effect on their children's bone health.
Lawlor commented that her team's study challenges the suggestions children's future bone health depends on the supplementation of their mothers with vitamin D during pregnancy.
Source: The Lancet
Published online ahead of print, doi:10.1016/S0140-6736(12)62203-X
"Association of maternal vitamin D status during pregnancy with bone-mineral content in offspring: a prospective cohort study"
Authors: Debbie A Lawlor, Andrew K Wills, Abigail Fraser, Adrian Sayers, William D Fraser, Jonathan H Tobias