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Study: Women born in December have lower risk of dying from cardiovascular disease

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(Vienna, 19 December 2019) In the past, many studies have looked at whether mortality from cardiovascular disease correlates with the time of year when a person was born. A research group led by Eva Schernhammer, Head of the Division of Epidemiology of MedUni Vienna's Center for Public Health, has now analysed data from the "Nurses' Health Study" and has shown that there does indeed appear to be a correlation between birth month and cardiovascular disease mortality. The study shows that women who were born in December have a lower risk of dying from a cardiovascular disease than women born between March and July. The study has been published in the prestigious British Medical Journal.     

There were already suspicions about a possible correlation between birth month and birth season and the probability of dying from cardiovascular disease. The research group led by epidemiologist Eva Schernhammer has now taken data from the "Nurses' Health Study", a US longitudinal study that has been running since 1976, as the basis for its prospective cohort study.

One of the biological hypotheses for the correlation between fatal cardiovascular disease and the season in which one was born is a possible vitamin D deficiency at birth, which would vary according to birth month. Another hypothesis is that higher socio-economic status, which was associated with a lower risk of cardiovascular disease, could potentially lead to preselection of a Winter confinement in better-off families. The study involved the comparison of data from 116,911 women, who worked as nurses. The researchers analysed overall mortality, as well as deaths specifically due to cardiovascular disease.

Three multivariable models were constructed to allow closer investigation of the risk factors: firstly age-standardised and then extended to include socio-economic risk factors such as education, financial circumstances, lifestyle and smoking behaviour. A third model also included factors such as body weight, cholesterol levels and physical activity and/or fitness.

A total of 43,248 deaths were recorded over the course of 38 years, 8,360 of these being associated with cardiovascular disease. No significant correlation was found between overall mortality (which also included e.g. cancer as the cause of death) and birth month or birth season. However, mortality associated with cardiovascular disease was higher among women born in the Spring and Summer than among women who were born in Autumn and Winter. The lowest mortality rate was found among women born in December and the highest among those born in April.

Says Schernhammer: "The correlation between birth month and a higher risk of dying from cardiovascular disease had already been documented. However, in our study, which is also one of the largest so far, we were able to largely exclude socio-economic factors as a reason for this correlation. Follow-up studies are now required to investigate the exact underlying pathophysiological mechanisms."

This study only included women, but the experts are assuming that the results would be similar for men.

Service: British Medical Journal
"Birth month, birth season, and overall and cardiovascular disease mortality in US women: prospective cohort study." Yin Zhang, Elizabeth E. Devore, Susanne Strohmaier, Francine Grodstein, Eva S. Schernhammer. DOI:10.1136/bmj.l6058.