The need for women, who are pregnant around this time of the year in countries like Ireland, to ensure they are getting enough vitamin D, is highlighted in a new study.
Taking a vitamin D supplement is advisable in countries where ultraviolet light levels are low between October and March.
It found the risk of babies born in April going on to develop multiple sclerosis as adults was highest.
It was lowest for infants born in October.
The risk has been linked to a pregnant woman's exposure to the sun. At latitudes greater than 52 degrees from the equator, insufficient ultraviolet light of the correct wavelength reaches the skin between October and March to enable the body to manufacture enough vitamin D during the winter months.
'The Journal of Neurology Neurosurgery and Psychiatry' said there was a significant excess risk of 5pc among those born in April.
The risk of developing the disease was 5pc to 7pc lower among those born between October and November.
Many pregnant women do not like taking any supplements during pregnancy but they are safe taking up to 10 micrograms of vitamin D a day.
The importance of pregnant women getting enough vitamin D has previously been stressed in studies showing that it strengthens their baby's bones and reduces their risk of rickets which could potentially lead to stunted growth.