It almost seems like a mystical correlation. Babies conceived at certain times of the year appear healthier than those conceived during other times. Now, scientists have shown that the surprising impression may actually be true — and they think they may know why it happens.
The work is “a really long-overdue analysis,” says economist Douglas Almond of Columbia University, who was not involved in the study. “This is maybe not quite a smoking gun,” he says, “but it’s much stronger than the previous evidence.”
As early as the 1930s, researchers noticed that children born in winter were more prone to health problems later in life: slower growth, mental illness and even early death. Among the proposed explanations were diseases, harsh temperatures and higher pollution levels associated with winter, when those expectant mothers and near-term fetuses might be most vulnerable.
But recently, as economists looked at demographics, the picture got more complicated. Mothers who are nonwhite, unmarried or lack a college education are more likely to have children with health and developmental problems. They are also more likely to conceive in the first half of the year. That made it hard to tease out the socioeconomic effects from the seasonal ones.