Health & Wellness

What birth month reveals about your risk of disease

Summer birthdays seem like the best — the weather is perfect for swimming, biking, and picnicking (much better that those parties winter babies have in stuffy buildings). But there’s another reason summer birthdays rock; babies born in the summer appear to be healthier according to a new British study.

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The new study highlights the importance of maternal health, researchers say.

“Children who were born in the summer were slightly heavier at birth, taller as adults, and went through puberty slightly later, relative to those born in winter months,” writes Ken Ong, programme leader at the Medical Research Council Epidemiology Unit, University of Cambridge, writes via email. The study was published in the journal Heliyon.

Ong and his colleagues looked at 450,000 births in the United Kingdom from the UK Biobank. Participants, ages 40 to 69, were recruited from the biobank, from 1946 to 1975. The researchers learned that summer babies weigh more at birth and experience delayed puberty; this leads to improved health outcomes for adults. Ong says the findings highlight the importance of maternal health.

“[The results] support the growing notion that promoting good health of mothers during, and even before, pregnancy has very long-lasting impacts on the next generation,” says Ong (who has a November birthday).

This study provides more evidence that birth month contributes overall health. In June, Columbia researchers examined 1.75 million records of New Yorkers born between 1900 and 2000. The study found that people born in certain months are at increased risk for certain diseases.

“What [this] tells us is not so much of when we should have babies but what contributes [to health] in the environment,” says Tatonetti, the Herbert Irving Assistant Professor of Biomedical Information at Columbia University. “[Birth month effects] are kind of small compared to things you can control.”

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Diet and exercise still play more into whether a person has a higher risk for cardiovascular disease than birth month. But Tatonetti (who has a May birthday) does believe that the relationship between birth month and diseases means that scientists still need to understand the mechanisms behind diseases.

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Summer babies could be healthier in Ong’s study because their mothers’ increased exposure to the sun and vitamin D. But Tatonetti says there are as many as 150 compounds that might contribute to why certain diseases are more likely to occur in certain months. And, he says that results in the United Kingdom or New York City might not apply to people everywhere.

While birth month’s influence on health remains unclear, here’s what science knows so far.

June, July, and August

“Women who were born in summer had higher birth weight and later puberty, which are both early life factors that have been linked to better health outcomes in adults,” says Ong.

May, June, July, August, and September

Women born these months are slightly less fertile than women born in other months.

October, November, December

Babies born in the latter part of the year might have a harder time paying attention. ADHD incidence increases as the year goes on, with November babies being the most likely to experience the disorder.

People born in November and October also experience an increased risk of respiratory, reproductive, and neurological illness. But babies born in December showed no increased risk of or protection from disease.

While that might seem like quite the health burden, people born in September, October, and November experience much less risk of cardiovascular disease.

January to June

People born in the first half of the year might want to watch their cholesterol and sodium intake as they are at a higher risk of cardiovascular disease, with those born in February, March, and April at the greatest risk. Yet babies born in these three months are much less likely to experience neurological problems.

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