Mothers expecting to give birth in the winter should seriously consider taking vitamin D supplements, new research suggests. A recent bone density study reveals that winter babies born to mothers who took vitamin D during pregnancy had healthier and denser bones than those born to mothers who took placebo pills.

However, researchers noted that taking the "sunshine vitamin" during pregnancy appeared to only benefit babies born in the gloomy winter months and not for those born in sunnier months.

"We found that vitamin D is safe and effective in raising levels in mothers whose babies are born during winter months," study author Cyrus Cooper said in a statement.

After analyzing data from over 1,100 pregnant British women, researchers found no differences in bone density between babies of women on vitamin D supplementation and those of women on placebo pills. However, the study revealed that vitamin D supplements did help winter babies of mothers who had inadequate levels of the sunshine vitamin during the last half of pregnancy.

"Babies' bones strengthen during the last stages of pregnancy. Since sunlight is our most important source of vitamin D, mothers' levels of vitamin D tend to drop from summer to winter, and babies born in the winter months tend to have lower bone density than those born during the summer," lead researcher Professor Nicholas Harvey of the University of Southampton said in a university release.

"Supplementing mothers with vitamin D during pregnancy counteracts the seasonal drop in maternal vitamin D levels and may help to ensure good bone development in these winter births," Harvey added.

The latest findings may have implications for health guidelines concerning routine vitamin D supplementation during pregnancy. While the American College of Obstetricians and Gynecologists recommend that pregnant women with vitamin D deficiency take supplements, British healthcare guidelines recommend vitamin D supplements to all expectant mothers.

"Supplementation of women with cholecalciferol 1000 IU/day during pregnancy did not lead to increased offspring whole-body BMC compared with placebo, but did show that 1000 IU of cholecalciferol daily is sufficient to ensure that most pregnant women are vitamin D replete, and it is safe. These findings support current approaches to vitamin D supplementation in pregnancy," researchers wrote in the study.

High bone density during infancy is important because it reduces the risk of osteoporosis and bone fractures in adulthood.

The findings are published in the journal Lancet Diabetes and Endocrinology.