Lower prenatal levels of vitamin D, the "sunshine vitamin," may mean that babies born in April have the highest risk of developing multiple sclerosis later in life while those born in October have the lowest risk, a new study suggests.
The findings show that pregnant women who live in countries with low levels of sunlight between October and March should take vitamin D supplements in order to protect their children from MS, according to the researchers.
Vitamin D is synthesized naturally by the skin as it makes contact with sunlight. During fall and winter months, however, people in northern countries may not receive sufficient amounts of sunlight on their skin to enable the body to make enough vitamin D, the study authors explained.
A team led by Dr. Ram Ramagopalan of Queen Mary University of London analyzed previously published data on nearly 152,000 people with MS in northern countries. They found that people born in April had a 5 percent increased risk of MS, while those born in warmer, sunnier months — between October and November — had a 5 percent to 7 percent reduced risk of the neurological disorder.
No data from countries in the southern hemisphere was analyzed by the researchers, largely due to a lack of studies.
The findings provide "the most robust evidence to date" that a person's month of birth affects their risk for MS. The results also highlight the need for studies to determine whether taking vitamin D supplements during pregnancy can help prevent MS in children, the researchers wrote.
Two experts in the United States said the findings make sense.
"I would agree that there is evidence that would support Vitamin D supplementation in pregnant women in certain areas," said Dr. Karen Blitz-Shabbir, director of the Multiple Sclerosis Center at the Cushing Neuroscience Institute, part of the North Shore-LIJ Health System in Manhasset, N.Y.
"We are well aware that populations further from the equator have a higher incidence of MS," she added. "We also have new studies emerging demonstrating vitamin D supplementation may be beneficial to people with MS. The full story on how vitamin D impacts this disease is still unfolding."
And Dr. Fred Lublin, director of the Corinne Goldsmith Dickinson Center for Multiple Sclerosis at the Mount Sinai School of Medicine, in New York City, said the study "provides further evidence for a link between birth month and risk of MS."
Still, he said that although "the authors raise the question of whether vitamin D supplementation could mitigate the risk, this would need to be proven in a clinical trial."
The study was published online in the Journal of Neurology, Neurosurgery and Psychiatry. Although it showed an association between birth month and MS risk, it did not prove a cause-and-effect relationship.