Summer kids more likely to grow up to be healthy adults

A new study from researchers at the Medical Research Council (MRC) Epidemiology Unit, University of Cambridge, United Kingdom suggests that girls born during the summer season are more likely to grow up to be healthy adults, EurekAlert reports. Researchers studied 500,000 individuals from the U.K. and determined whether their birth month had an effect on birth weight, onset of puberty, and height as adults.

The study, which was published in the journal Heliyon, found that babies who were born during summer had slightly heavier birth weight, were taller as adults, and gone through puberty slightly later than their counterparts who were born during winter. Researchers believe that higher exposure to sunlight and vitamin D in the second trimester of the pregnancy could be one reason why the children of summer turn out somewhat healthier.

The study's lead author, Dr. John Perry explained, "When you were conceived and born occurs largely 'at random'—it's not affected by social class, your parents' ages or their health—so looking for patterns with birth month is a powerful study design to identify influences of the environment before birth."

Researchers also found that birth month affects birth weight and the timing of a girl's puberty onset. Newsweek reports that this study delves more into the phenomenon called "fetal programming hypothesis," wherein the environment in the mother's womb influences the baby's development, which later on has an impact on the baby's later life.

Dr. Perry and his team believed that childhood growth and development, as well as the timing of puberty is related to early life and later health, and therefore took this into consideration for the study. Researchers analyzed 450,000 men and women from the U.K. Biobank study, a major national health resource that provides data on UK volunteers to shed light on the development of diseases.

Researchers found that children who were born in June, July, and August had heavier birth weight and taller height as adults. It was also the first time a study has uncovered the link between birth month and the onset of puberty, as those who were born in summer had started puberty later.

"This is the first time puberty timing has been robustly linked to seasonality," Dr. Perry said. "We were surprised, and pleased, to see how similar the patterns were on birth weight and puberty timing. 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."

According to research, the differences are attributed to sunlight exposure, as mothers may have gotten more sunlight during the pregnancy.

According to Dr. Perry, "We don't know the mechanisms that cause these season of birth patterns on birth weight, height, and puberty timing. We need to understand these mechanisms before our findings can be translated into health benefits. We think that vitamin D exposure is important and our findings will hopefully encourage other research on the long-term effects of early life vitamin D on puberty timing and health."