A little woolen hat, a few garlands in the living room… and a birth certificate dated December 24 or 25. Behind the touching image of the Christmas baby, researchers wondered whether coming into the world in the depths of winter left a lasting mark on the body, long after the first photos under the tree.
A British team sifted through the health data of nearly 450,000 adults, published in 2015 in the journal
Heliyon. Their work suggests that the season of birth, especially winter, is associated with birth weight, final height and the timing of puberty in girls. It remains to be understood what is hidden behind this famous detail.
Christmas baby: what the study says about height and puberty
The health records analyzed show that babies born in December, January or February have on average a slightly lower birth weight than those born in summer. Once adults, these “Christmas children” tend to be slightly smaller than their peers born in June or July. For girls, puberty occurs on average a little earlier when the birth took place in the middle of winter.
The authors emphasize that these are differences observed at the population level, not individual predictions. The variations remain modest, without pathological character, but outline a typical profile of the “winter baby” when we compare very large groups of people over several decades.
The key detail would play out… in the sunlight
To explain these differences, researchers look to the sun, and therefore vitamin D. For a baby born at Christmas, the second and third trimesters of pregnancy take place in autumn then at the beginning of winter, when the light drops. The fetus then receives less vitamin D synthesized by its mother’s skin than a baby whose end of gestation falls in the middle of August.
The curves obtained also stick to the sunshine profile of the second trimester of pregnancy. Vitamin D plays a known role in bone mineralization and also intervenes in certain hormonal adjustments; it therefore becomes logical that the season of birth can, at the margin, influence growth and the timing of puberty. The rest then comes down to family genetics, diet and lifestyle.
Baby born in winter: what parents can remember
For parents, the message is above all reassuring: these differences remain small and, in France, infants almost systematically receive vitamin D supplementation in order to avoid real deficiencies. During fall or winter pregnancy, certain actions can support this contribution, always with the advice of a health professional:
- Discuss vitamin D during follow-up consultations;
- Put more fatty fish and eggs on the menu;
- Take advantage of the sunny hours, even if short, by going out regularly.
The season of birth therefore appears to be a little boost, or brake, among other factors that are much more serious for height and puberty. Many children born in December grow taller than their summer friends, others do not; Above all, the figures from the study reveal a scientific curiosity which gives additional depth to the story of this Christmas baby.