No significant associations seen between birth month, birth season, and overall mortality
THURSDAY, Dec. 19, 2019 (HealthDay News) — Women born in the spring and summer may have a slightly higher risk for cardiovascular disease mortality than women born in autumn, according to a study published online Dec. 18 in The BMJ.
Yin Zhang, Ph.D., from Brigham and Women’s Hospital and Harvard Medical School in Boston, and colleagues conducted a prospective cohort study to examine the associations between birth month and season and overall and cardiovascular disease mortality risk. Data were included for 116,911 female registered nurses followed for 38 years.
The researchers documented 43,248 overall deaths during 4,136,364 person-years of follow-up since enrollment, including 8,360 cardiovascular disease-related deaths. No significant associations were seen between birth month, birth season, and overall mortality in fully adjusted multivariable analyses. Increased cardiovascular disease mortality was seen for women born from March to July compared with those born in November (hazard ratio for March, 1.09 [95 percent confidence interval (CI), 0.98 to 1.21]; April, 1.12 [95 percent CI, 1.00 to 1.24]; May, 1.08 [95 percent CI, 0.98 to 1.20]; June, 1.07 [95 percent CI, 0.96 to 1.19]; and July, 1.08 [95 percent CI, 0.98 to 1.20]). The highest and lowest cardiovascular disease mortality rates were seen for those born in April and December, respectively, with a relative difference of 17.89 percent between those months. Compared with women born in the fall, those born in spring and summer had a higher risk for cardiovascular disease mortality (hazard ratios, 1.10 [95 percent CI, 1.04 to 1.17] and 1.09 [95 percent CI, 1.03 to 1.16], respectively). These associations were not changed by adjustment for familial and socioeconomic factors.
“This study supports that the associations of fetal and early life factors with cardiovascular disease mortality could relate to a small but real seasonal effect of fetal or early life factors in later life,” the authors write.
Several authors disclosed financial ties to the biopharmaceutical industry.
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