The study — using data from the Nurses’ Health Study, which has followed more than 100,000 American female nurses since 1976 — looked at associations between death from cardiovascular disease and birth month and season. The researchers found that women born in the spring and summer had “a higher cardiovascular disease mortality” than those born in the fall.
More specifically, they found a link between higher rates of death from cardiovascular disease and women born between March and July, as compared to those born in November. Researchers also found that women born in April had the highest cardiovascular disease mortality rates, while those born in December had the lowest rates.
More research is needed to understand how birth month and birth season might influence a person’s health, but it’s part of what’s called the “fetal origins hypothesis” — essentially, “how prenatal exposures can affect babies and how those exposures may manifest into adulthood,” Michael Cackovic, an ob-gyn who specializes in high-risk pregnancies at The Ohio State University Wexner Medical Center, tells Yahoo Lifestyle.
“Prior studies suggested that these may include seasonal fluctuations in nutrition availability, infections and inflammatory causes, climatic temperature and air pollution, or sunlight exposure — maternal vitamin D levels and solar cycles — as well as near-birth familial/socioeconomic factors,” the co-author of the study, Eva Schernhammer, MD, of Brigham and Women’s Hospital, tells Yahoo Lifestyle.
Sun exposure during pregnancy, which affects vitamin D levels, seems to be particularly influential, at least in terms of a baby’s future heart health. “Maternal vitamin D status during pregnancy, as a correlate of season and month of birth season, has been described as a suggestive or probable factor affecting adult cardiovascular disease risk,” Schernhammer tells Yahoo Lifestyle.
This isn’t the first study to look at birth month and its influence on health. The study authors pointed out that research in Britain (one study linked being born during cold weather months with increased rates of coronary heart disease and insulin resistance) and Canada has found similar associations. A 2016 Canadian study of more than 8,300 people looking at associations between birth month and heart health found that hypertension and coronary heart disease “were most prevalent in those who were born in January and April.”
Cackovic says that previous research has also shown a link between October and November birth months and “a risk of respiratory [such as acute bronchitis], reproductive and neurological illnesses.” He says, “This particular study also supports previous studies that spring months, specifically January to June, had a higher risk of cardiovascular disease.”
He calls this a “fascinating area of research,” adding, “This is really new and cutting-edge research — therefore, we are not completely sure in which direction this will take us or how it may change preventative healthcare.”
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