Researchers who tracked 6.19 million Swedish residents found that people born in November had the lowest adult mortality, while spring births carried the highest. The effect was small but statistically robust, and it held across decades of records.
A separate analysis of 1,574 verified American centenarians pushed the finding further. Those born between September and November had 37 to 47 percent higher odds of reaching age 100 than siblings born in March.
The pattern is not new. In 2001, demographers Gabriele Doblhammer and James Vaupel showed that autumn-born Austrians and Danes lived several months longer, on average, at age 50 than their spring-born peers.
Where the effect actually shows up
The Swedish national cohort, published in PLoS ONE in 2013, followed Swedish-born residents alive on 1 January 1991 through the end of 2010.
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Between the ages of 50 and 80, April births carried a 42 per thousand higher hazard than November births, with May close behind.
Above age 80 the gap shrank, and between 30 and 50 the researchers found no reliable difference. Their broad conclusion was that spring and summer births die sooner than autumn births from midlife onward.
The US centenarian study, published in the Journal of Aging Research in 2011 by Leonid and Natalia Gavrilov, used siblings as controls to strip out family and lifestyle differences. September, October and November births still came out ahead.
A cohort of roughly 211,000 people in Taiwan, published in Naturwissenschaften in 2024, found a 5 percent higher risk of all-cause mortality among spring births compared with winter births, even after adjustment for medical conditions.
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Why season of birth might matter
Researchers keep circling back to conditions in the womb. A mother pregnant through the darker months produces less vitamin D from sunlight, which may shape fetal bone, immune and cardiovascular development.
Seasonal infections are the second candidate. A fetus developing during flu or respiratory virus season may face immune signals that leave a measurable trace decades later.
Columbia University's phenome-wide analysis of 1.75 million patient records identified 55 diseases with a statistical link to birth month. March births showed elevated cardiovascular risk, while October births carried a higher load of respiratory conditions.
The effect is real, but small
Roughly 2 to 5 percent of the variation in adult lifespan tracks with birth month.
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Smoking, diet, exercise and blood pressure still dominate personal risk by a wide margin, and no one can change the season they were born in.
The actionable piece sits earlier in life. The Columbia team flagged prenatal vitamin D status as the plausible target, and the US Office of Dietary Supplements currently sets the recommended daily intake at 600 IU of vitamin D during pregnancy.
Doblhammer and Vaupel also documented Australian data from the Southern Hemisphere, where the pattern shifted by six months. British immigrants to Australia kept the Northern Hemisphere pattern they were born with.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.