PEOPLE born in the summer (equivalent to peak rainy season in Nigeria) are more likely to be healthy than those who arrive during other times of the year, new research suggests.
The phenomenon could be caused by mothers getting more sun in pregnancy – and passing on higher quantities of vitamin D to their unborn infant.
A study of almost half a million British adults found babies born in June, July, and August were heavier at birth and taller as adults.
For the first time the research also revealed girls born in the summer started puberty later – an indication of better health in adult life.
Early puberty in girls has been linked with a higher risk of diabetes, heart disease or breast cancer.
Study author Dr. John Perry, of Cambridge University, said: “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.”
His team compared the growth and development of around 450,000 men and women from the United Kingdom (UK) Biobank study – a major national health resource that provides data on UK volunteers to shed light on the development of diseases.
Perry explained: “This is the first time puberty timing has been robustly linked to seasonality. We were surprised, and pleased, to see how similar the patterns were on birth weight and puberty timing.
“Our results show birth month has a measurable effect on development and health, but more work is needed to understand the mechanisms behind this effect.”
Previous research has shown children born between June and October are likely to be slightly taller and have bigger bones than winter-born children – believed to be related to vitamin D exposure during pregnancy.
Babies born in autumn and winter are more likely to develop food allergies – with sunlight exposure during pregnancy and vitamin D levels also thought to play a role in this.
Asthma is also more common in autumn-born children – and one theory for this is increased exposure to allergens, such as house dust mites, during the first few months of life – because of the worse weather.
The latest findings, published in the journal Heliyon, declare birth month affects both the weight of the newborn and when a girl starts puberty.
Both of these have an impact on overall health in women as adults. Furthermore, the environment in the womb leads to differences in early life – including before birth – that can influence health in later life.
For the study, Perry and his colleagues looked at whether birth month had an effect on birth weight, onset of puberty and adult height .
The team found that children born in the summer were slightly heavier at birth, taller as adults and went through puberty slightly later than those born in winter months.
Previous studies have reported certain season of birth effects such as on birth weight and various other health outcomes so Perry and colleagues decided to look more closely.
They believe the differences between babies born in summer and winter could be down to how much sunlight the mother gets during pregnancy – since that in part determines her vitamin D exposure.
Perry said: “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 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.”