Vit D supplements for preggers should be customised for ensuring the effects

Vitamin D supplements are less effective at raising vitamin D levels in pregnant women if they deliver their babies in the winter, have low levels of vitamin D early in pregnancy or gain more weight during pregnancy, a new Southampton study has shown.

The findings showed pregnant women respond differently to vitamin D supplementation depending on their individual attributes.

The University of Southampton researchers suggest that supplement levels should be tailored according to individual risk factors.

Vitamin D is a hormone that helps the body absorb calcium. It plays a crucial role in bone and muscle health. The skin naturally produces vitamin D after exposure to sunlight but people also obtain smaller amounts of the vitamin through foods, such as milk fortified with vitamin D.

Evidence suggests vitamin D deficiency during pregnancy can harm maternal health, fetal development and the child's long-term skeletal health.

Study leader Nicholas Harvey commented, "It is important for pregnant women to have sufficient levels of vitamin D for the health of their baby. Our study findings suggest that in order to optimise vitamin D concentrations through pregnancy, the supplemental dose given may need to be tailored to a woman's individual circumstances, such as the anticipated season of delivery."

The Maternal Vitamin D Osteoporosis Study (MAVIDOS), is a multi-centre, double-blind, randomised, placebo-controlled trial of vitamin D supplementation in pregnancy. More than 800 pregnant women were recruited and randomised to take either 1000 units (25 micrograms) of vitamin D every day or a matched placebo capsule from 14 week's gestation until delivery of the baby.

Analysis showed that participants who received the vitamin D supplement achieved different levels of vitamin D in the blood, even though they received the same dose. Researchers found women who delivered in the summer, who gained less weight during pregnancy and who had higher vitamin D levels early in pregnancy tended to have higher levels of vitamin D in the blood than their counterparts. Women who consistently took the supplement also had higher levels of vitamin D than participants who did not.

"Our findings of varied responses to vitamin D supplementation according to individual attributes can be used to tailor approaches to antenatal care," said researcher Cyrus Cooper. "This work forms part of a larger programme of research at the MRC Lifecourse Epidemiology Unit, University of Southampton, addressing the early life determinants of bone development, and will inform novel strategies aimed at improving bone health across future generations."

The study has been published in the Endocrine Society's Journal of Clinical Endocrinology and Metabolism.