Children, especially girls, born during summer months are more likely to mature into healthier adults than those born in winter months, researchers say.
Scientists at the University of Cambridge in England suggest mothers who have greater sun exposure during their pregnancy's second trimester, which, in turn, increases an unborn baby's exposure to vitamin D, could be a reason why, although they acknowledge additional research is needed.
The birth month can affect both birth weight and the point at which a girl starts puberty, factors that can have an impact on a woman's overall health as an adult, the researchers say in their study published in the journal Heliyon.
For their study, they compared growth and development data on about 450,000 men and women, using information from the United Kingdom Biobank, a major national health database.
Babies born in June, July and August had heavier birth weights and grew taller as adults, the data showed.
The research also found girls born in summer months began puberty later, known to be indicative of better health in adulthood.
"This is the first time puberty timing has been robustly linked to seasonality," says study lead author John Perry.
Similar patterns were seen on both birth weight and the timing of puberty, he says.
"Our results show that birth month has a measurable effect on development and health, but more work is needed to understand the mechanisms behind this effect," he says.
A significant difference in the amount of an unborn baby's vitamin D exposure seems one likely mechanism, but while the study strongly suggests a possible link, more studies will be needed to confirm that, the researchers say.
"We need to understand these mechanisms before our findings can be translated into health benefits," says Perry.
When conception and birth occur is largely random, he points out, and unaffected by a family's social class or the ages or health of the parents, making a study of birth months a powerful way to identify how the environment during pregnancy influences health and development.
The researchers emphasize that, although their study found a link between birth month and some predicted health outcomes, it cannot be taken as proving a cause-and-effect relationship.
