It has long been known that babies born between the months of February and April are 10% more likely to develop schizophrenia than those born at other times of the year. Some theorists have suggested that flu contracted while the babies brain is developing could be the cause - since flu outbreaks occur more often during the winter months. Others, however, such as John McGrath have suggested that it may be that babies brains do not develop correctly due to low levels of vitamin D.