London | Babies who are born in the summer are slightly heavier at birth, taller as adults and go through puberty slightly later than those born in winter months, a new UK study has found. Researchers said that more sunlight and therefore higher vitamin D exposure in the second trimester of pregnancy could explain the effect, but more research is needed.
Researchers said that birth month affects birth weight and when the girl starts puberty, both of which have an impact on overall health in women as adults. The environment in the womb leads to differences in early life including before birth that can influence health in later life. This effect, called programming, has consequences for development throughout childhood and into adulthood.
The researchers behind the new study, from the Medical Research Council (MRC) Epidemiology Unit, University of Cambridge, UK, looked at whether birth month had an effect on birth weight, onset of puberty, and adult height. They found that children who were born in the summer were slightly heavier at birth, taller as adults and went through puberty slightly later than those born in winter months.
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, said Dr John Perry, lead author of the study.
The study compared the growth and development of around 450,000 men and women from the UK Biobank study, a major national health resource that provides data on UK volunteers to shed light on the development of diseases. The results showed that babies born in June, July, and August were heavier at birth and taller as adults. For the first time, the study also found that girls born in the summer started puberty later an indication of better health in adult life. This is the first time puberty timing has been robustly linked to seasonality, said Perry.
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, Perry said. The researchers believe that the differences between babies born in the summer and the winter months could be down to how much sunlight the mother gets during pregnancy, since that in part determines her vitamin D exposure.
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