Kid in summer
A boy eats an ice cream in the 32 degree Celsius heat on the first weekend of the summer school holidays at the swimming pools in Kriens July 10, 2010. Reuters/Romina Amato

Children who were born in the summer are more likely to grow up as healthy adults, according to a new study. This may be because mothers who were exposed to more sunlight received a higher dose of vitamin D, according to team of researchers from the Medical Research Council Epidemiology Unit at the University of Cambridge in UK.

The study, which appeared in the journal Heliyon, suggests that birth month affects a child's birth weight and onset of puberty, both of which have an impact on overall health in women as adults. The researchers 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.

Perry and his team decided to study more closely the impact of birth month since they believed that childhood growth and development is an important link between early life and later health. In the study, the researchers compared the growth and development of approximately 450,000 men and women. The information came from the UK Biobank study, a major national health resource that makes data readily available for researches on the development of diseases.

The study revealed that babies born in June, July and August were heavier at birth and taller as adults. The researchers also found that girls born in the summer started puberty late, which indicates better health in adult life.

Perry said that this is the first time puberty timing has been robustly linked to seasonality. While their findings show that the birth month has a measurable effect on development and health, he noted that more work is needed to understand the mechanisms behind this effect.

The researchers also believe that babies born in the summer are different from those born in winter months because of how much sunlight the mother got during pregnancy. “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,” Perry said.

A growing number of studies show that the season of birth yields certain effects on birth weight as well as various health outcomes. A 2003 research published in the Journal of Nutrition revealed that African-American babies born in the summer and fall were smaller than those born in other seasons.

Babies of African-American and Puerto Rican descent were also found to gain less weight in their first four months if they were born in the fall. In April 2008, a research that appeared in the journal Ophthalmology claimed that moderate and severe nearsightedness is highest for babies born in the summer months.

Babies born in the fall were also observed to have a 9.5 percent risk of having food allergies, compared with 5 percent for babies born in June and July. Meanwhile, those who were born in November or December were found to be three times more likely to suffer from eczema and wheezing. These findings were detailed in the Journal of Epidemiology and Community Health in 2010.

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