People born in spring and summer have a greater risk of dying from heart disease, claims study
The time of the year you are born might be linked to your risk of dying from heart disease later in life, suggests a large US study.
Those born in the spring (March to May) and summer (June to August) had a significant increase in death from heart disease, compared with those born in the autumn (September to November), according to researchers from Brigham and Women's Hospital and Harvard Medical School, Boston.
People born in April had the highest cardiovascular disease deaths, and those born in December had the lowest, shows analysis.
According to researchers, reasons for these differences are not well understood but could include seasonal fluctuations in diet, air pollution levels, and availability of sunlight before birth and in early life.
A total of 1,16,911 US women participating in the Nurses' Health Study were eligible for inclusion in the current research work. The registered nurses were recruited to the Nurses' Health Study in 1976 to examine links between birth timing and overall death, and death from cardiovascular disease.
The participants were 30 to 55 years at the start of the study and they completed a detailed health and lifestyle questionnaire every two years. Death certificates and medical records were used to identify causes of death over 38 years of follow-up (1976-2014).
During 38 years of follow-up, more than 43,248 deaths were documented over the study period, including 8,360 cardiovascular disease deaths. The mean age at death for those who died from cardiovascular disease was 74.6 years.
In addition to cardiovascular disease, the main causes of death included cancer, and others such as neurodegenerative disease, respiratory disease, or infections, says the study funded by the Center for Disease Control and Prevention (CDC), and the NIH/National Cancer Institute.
After taking into account a range of family history, economic and social factors, researchers found that women born in the spring and summer had a slight but significant increase in cardiovascular death compared with those born in the autumn.
The researchers found no significant association between birth timing and overall death. The analysis shows that compared to women born in November, more women died from heart diseases if they were born between March and July, peaking in April.
Meanwhile, women born in December had the lowest cardiovascular disease-related death. In terms of birth seasons, higher cardiovascular disease-related death was observed among women born in the spring and summer compared with those women who were born in the autumn.
Researchers say since this is an observational study, they cannot establish it.
"Compared with women born in November, higher cardiovascular disease mortality was observed among those born from March to July (hazard ratio for March 1.09, April, 1.12, May 1.08, June 1.07, July 1.08), with the highest cardiovascular mortality for those born in April, and lowest among those born in December (0.95)," says the study published in The BMJ.
"Women born in the spring and summer had higher cardiovascular mortality (hazard ratio for spring 1.10, summer 1.09) than those born in autumn," it adds.
It further states: "The relative difference between the lowest and highest risk month was 17.89%, and this difference between the lowest and highest risk season was 10.00%."
According to the research team, the findings support the view that associations of fetal and early life factors with cardiovascular disease death could relate to a "small but real seasonal effect of fetal or early life factors" in later life.
"Further investigations are required to confirm these findings and reveal mechanisms of these seasonal birth month effects in cardiovascular disease mortality," say researchers in their findings.