Why Kiwis born in May are likely to outlive the rest of us

People born in December have been rejoicing in recent weeks with viral news articles declaring that people born in the final month of the year are most likely to live the longest.

But unfortunately for them, this only applies to the northern hemisphere, and in the southern hemisphere, it's the May babies that are most likely to outlive the rest of us.

A number of UK websites this month published articles that quoted studies that found people born in autumn and early winter live longer than people born in spring and early summer.

The reason for this is said to be that while in utero, they're exposed to more sun towards the end of pregnancy and therefore soak up more vitamin D.

But data from Australia shows that in the southern hemisphere, the pattern is shifted by half a year, and it's those born in May that have the most longevity, while December babies have the shortest lifespan.

Lifespan depends on month of birth - graph
Deviation in remaining lifespan of people born in specific months from the average remaining lifespan at age 50. In the Northern Hemisphere countries of Denmark (green line) and Austria (blue line), the people born in the fourth quarter of the year live longer than those born in the second quarter. For Australia (red line), the pattern is shifted by half a year. Photo credit: Gabriele Doblhammer and James W. Vaupel

The findings from the study Lifespan Depends on Month of Birth, published in the US's National Center for Biotechnology Information (NCBI), are based on population data with more than a million observations. 

It compared the lifespans of Austrians, Danes and Australians, and found differences in adult lifespan by month of birth decreased over time and were more marked in those aged 50+.

"We have found that month of birth and remaining life expectancy at age 50 are related," the study's authors Gabriele Doblhammer and James W Vaupel wrote.

Researches found the difference in lifespan between the spring and autumn born is twice as large in Austria (0.6 years) as in Denmark (0.3 years).

In Australia, it was 0.35 years, with the mean age at death of people born in the second quarter of the year 78.00, while those born in the fourth quarter die at a mean age of 77.65 years.

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