The month a baby’s born may influence how long the child lives, according to an Italian study that says in the Northern Hemisphere, children born in spring and summer have shorter lifespans than those both in autumn and winter.

The opposite is true in the Southern Hemisphere, where spring and summer babies live longer.

In a new study published in Demographic Research, researchers from the University of Florence and the University of Bologna used three lenses to look at the effect of birth month on the lifespan of adults who were at least 50. They looked within families to see factors on the family level that might account for differences in how long relatives lived. They looked at birth and death records over 200 years, using Census data from 1700 to 1899. And they looked at geographical variation.

“The effect is relatively consistent across cohorts, geographical census area and between and within families,” they wrote, noting they find “residual evidence that in utero debilitation may account for this result.”

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Experts believe that conditions at the time of a baby’s birth have profound impact on what kind of healthy start that child gets. And some of the effects set the course for a lifetime, making it crucial babies get off to a strong start.

Examinations of birth month and a possible relationship with when someone dies have been around for a couple of decades, at least. And studies have also examined possible links between birth month and earnings, having certain diseases and more. One study found, for instance, that babies born in May are less apt to develop certain serious diseases. Another found being born in winter or spring “were significantly associated with all-cause and cardiovascular disease mortality in rural areas of China.” A Columbia University data study found birth month “helps determine your risk” for asthma, ADHD, heart disease and 39 other common medical problems.

None of those have anything to do with astrology. While covering a study that found those born in December, January and February have a 7% lower risk of dementia later in life compared to the babies born in June, July and August, New Scientist said experts say birth month is a “marker for environmental conditions.”

“Summer-born babies are younger when they face respiratory infections of their first winter, for example,” the article said. “And in the past, babies born in spring and summer would have been in late gestation when the supply of fresh fruit and vegetables from the autumn harvest would have largely run out. Pollution from wood fires or coal heating might also have played a role.”

In a 2001 study of life span and birth month, researchers said birth month “proxies environmental exposures leading to in utero debilitations, which in turn shape later-life mortality patterns.” But while some studies repeated the finding over the intervening years, others didn’t find an association.

Those 2001 study researchers called their results “consistent with the finding that, at the turn of the last century, infants born in autumn had higher birth weights than those born in other seasons. Furthermore, differences in adult lifespan by month of birth decrease over time and are significantly smaller in more recent cohorts, which benefited from substantial improvements in maternal and infant health.”

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The new study says that what type of in utero debilitation might make the difference isn’t clear. The factors influenced by time of year could include maternal nutrition, climatic conditions and infectious diseases, they note. And certainly in the 200-year study of the 1700s and 1800s, the food that was available would vary by season.

“In utero nutrition has been shown to have strong effects on children’s health and survival at birth and in infancy, and has also been linked to the onset of diseases later in life,” the study said. But the authors note that studies have shown mixed evidence that it affects adult mortality.

As for infections, they note that “food and water-borne diseases follow seasonal patterns and may also contribute in utero debilitation and have long-lasting consequences for individuals’ lives.”

They note caveats, too, including the fact the data isn’t representative, though other factors lead them to believe the findings are not biased.

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