It is fascinating to think that when we are born can influence our later health.

Women who were born in the summer are more likely to be healthy adults, according to new research published in the journal Heliyon.

The authors of the study, which involved almost half a million people in the UK, say more sunlight - and therefore higher vitamin D exposure - in the second trimester of pregnancy could explain the effect.

A commonly held preconception is your birth month affects your birth weight. In the case of girls it can impact when puberty starts. Both of these have an impact on overall health in women as adults.

What happens in utero then leads to differences in early life - including before birth - that can influence health in later life. This effect is called programming. It has consequences for development throughout childhood and into adulthood.

New research challenges assumptions

Researchers 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.

Conception and birth occurs largely "at random" – meaning your conception or birth is not affected by social class, your parents' ages or their health. Therefore the authors state that looking for patterns with birth month can identify influences of the environment before birth.

Previous studies have reported certain effects of the season of birth, for example on birth weight and various other health outcomes.

It is known that childhood growth and development, including the timing of puberty, is an important link between early life and later health.

The researchers compared the growth and development of around 450,000 men and women from the UK Biobank study.

The results reveal that babies born in June, July, and August were heavier at birth and taller as adults. The study also revealed that girls born in the summer started puberty later - an indication of better health in adult life.

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.

It is thought that vitamin D exposure is important and the effects of early life vitamin D impacts on puberty timing and health.