why people born at July, June and August are heavier at birth and taller at adulthood

here’s more reason to be jealous of summer babies than all
those birthday parties by the pool: They may be healthier adults,
according to a new study. University of Cambridge scientists
surveyed roughly 500,000 Britons aged 40 to 69 for their birth
dates, height, weight, and the age at which females had their first
period, reports the Times, per the Australian. People born in
June, July, and August were heavier at birth and about 1/8 of an
inch taller in adulthood than those born in December, January,
and February, while women born in summer had their first
menstrual cycle weeks after those born in winter; like heavier
birth weight, later puberty tends to positively impact health in
later life, per a press release.
Why the
discrepancies? Scientists suspect it has to do with the amount
of sun exposure mothers received, and thus the amount of
vitamin D passed to the fetus, during pregnancy. “Vitamin D is
important for bone development and may act as a rate-limiting
factor for growth,” the authors write in the journal Heliyon. And
while earlier studies have shown a link between birth date and
height, “this is the first time puberty timing has been robustly
linked to seasonality,” says a researcher. Total sunlight
exposure led to stronger effects in the later six months of
pregnancy, and not in the first three months after birth, which
supports the idea of “fetal programming”: that the environment
in the womb can affect a person’s health later, per Medical News
Today. Researchers note the study participants were conceived
before pregnant women were advised to take vitamin D
supplements. (A lack of vitamin D may have killed this famous
composer.)