Leonid Gavrilov and Natalia Gavrilova are a good resource for this sort of demography and epidemiology of aging. [1] In particular they have a lot of material on season of birth effects. [2]
Tangentially related to the seasonal effects is data suggesting that solar cycles also influence longevity, possibly through quite indirect responses to levels of UV exposure in pregnant women. [3] You can see how this might be relevant to season as well, but it is only one of a number of mechanistic theories on the subject.
This sort of thing ties back in to application of reliability theory to aging [4], wherein to make the models fit the observed data individuals have to be born with a preexisting non-zero damage load.
The differential exposure to UVB, that is, sunlight, was the first thing I thought of reading this article. It is especially likely among people born in the industrial-era 19th century, at a time before the nature of the link between health and sunlight was clearly identified.
Around a hundred years ago, the role of UV in preventing rickets was confirmed. By the 1930's, vitamin D supplementation of foods became widespread, and the most obvious manifestations of deficiency (e.g., rickets) essentially disappeared. Studied intensively since the 1930's numerous effects of D (or lack of it) have been reported, and recently interest has exploded.
Increasingly evidence implicates low vitamin D levels in a wide range of conditions, such as autoimmune disorders, cancer, and metabolic disease, that are likely contributors to reduction of life expectancy.
Seasonality of vitamin D level is well known. In northern latitudes (>=45th parallel) the nadir occurs around March-April, and the peak is measured on average in September-October. The timing of these fluctuations appears quite congruent with the article's assertions about life expectancy, so it's reasonable to think there is a connection.
But the data in the post does not seem to be super correlated to seasons. You can see that the decrease in life expectancy occurs way before spring (as soon as February) which is still supposed to be a winter month. So the season link is weak.
The correlation is in terms of fractions of a year so they add up to an average of plus-or-minus a few month over a lifetime. The three curves don't seem to have a very close relationship to each other though there are some similarities.
I assume that if they are getting a meaningful correlation, it is over a large amount of data. It seems logical that at large scale, date born would correlate with a variety of things in various areas - social class and wealth come to mind.
I think it's a matter of taste whether one says "wow, throw enough data together you find unexpected correlations" or "garbage in, garbage out". A life insurance company could eek out a bit of profit changing its price structure on this data - if it didn't have far more to lose if the use of such tactics became public.
I bet someone can use this to claim astrology has validity too.
Would be interesting to look at the 'stresses' that occur within schools. My 11 year old daughter was born on the 30th of August. Ergo she is the youngest in the year at school. She is studying with people that have a year of development on her. She is doing fantastically well but works hard to achieve that result.
My hypothesis is that the age cut off in schools, unduly puts stress on the younger children in a class, that long term, impact on health in later years. In effect which month you are born in affects the stress you will feel during your school years as it will be inherently 'harder' for you.
I'd think the opposite. Since she is used to having to work hard from a young age, she will be more successful in life.
Others who coasted through—whom were used to everything being relatively easier—will not have the experience she has already accrued when faced with a harder challenge.
I'm from Slovenia, where it's exactly the opposite. Being born in November, I was among the younger people in my class. The cut-off point was January or February (of the next calendar year). So it could be that the more stress you have, the longer you live (better personal/immune system development). Alternatively, younger classmates (i.e. people that go to school with peers that are in average older) achieve accelerated development (because they hang out with "more developed" kids) which could also somehow affect life expectancy.
It could also have something to do with their development in school. After all the school year is the same for all. Some kids are up to 11 months younger!
This is an area which I've personally experienced, having spent the first half of my school years in Europe, and being a few days shy of the cut-off point for being held back another year, I was always the youngest in my class (I guess on a large enough population, it would mean that similar kids are the smallest as well, on average).
Later on I switched to a southern-hemisphere school, which was out of phase by 6 months, and I was all of a sudden roughly average age in class. Not that it had a huge impact on me, but it was noticeable, which probably means it has some effect on average.
The effect of school could be isolated by comparing different countries with different cutoff dates. I believe the American and UK systems are based on age when the school year starts, so the youngest in the class were born in August. Sweden groups classes by birth year, so the youngest were born in December. The Japanese school year starts in spring.
This is interesting. They seem to think it is in utero effect. Maybe Vitamin D?
I wondered if they considered if the cause is age when starting school. I know that birth month has pretty powerful effects for educational attainment.
I was wondering about that. I read somewhere else about the birth month effect for professional athletes. Kids whose birthday falls just after the season of their sport starts are up to a year older, bigger and stronger than their peers born earlier in the year, which boosts their confidence to the point that fewer of them quit.
Very curious. Information about people in the tropics would be interesting since climate doesn't vary as much there. I know in Madras, India it was hot pretty much all of the time, except when it rained.
I didn't fully read it but doesn't it look like there is potentially a big survivorship bias in the data?
They touch the subject with their 3rd hypothesis but in general it's possible that you still have a higher life expectancy being born from April-June in the Northern Hemisphere because you have increased chances of reaching 50.
So why this limit of 50 years? What is the expected lifespan for newborns depending on their month of birth?
[+] [-] reasonattlm|11 years ago|reply
Tangentially related to the seasonal effects is data suggesting that solar cycles also influence longevity, possibly through quite indirect responses to levels of UV exposure in pregnant women. [3] You can see how this might be relevant to season as well, but it is only one of a number of mechanistic theories on the subject.
This sort of thing ties back in to application of reliability theory to aging [4], wherein to make the models fit the observed data individuals have to be born with a preexisting non-zero damage load.
[1]: http://longevity-science.org/
[2]: http://longevity-science.org/Season-of-Birth.pdf
[3]: http://rspb.royalsocietypublishing.org/content/282/1801/2014...
[4]: https://en.wikipedia.org/wiki/Reliability_theory_of_aging_an...
[+] [-] jrapdx3|11 years ago|reply
Around a hundred years ago, the role of UV in preventing rickets was confirmed. By the 1930's, vitamin D supplementation of foods became widespread, and the most obvious manifestations of deficiency (e.g., rickets) essentially disappeared. Studied intensively since the 1930's numerous effects of D (or lack of it) have been reported, and recently interest has exploded.
Increasingly evidence implicates low vitamin D levels in a wide range of conditions, such as autoimmune disorders, cancer, and metabolic disease, that are likely contributors to reduction of life expectancy.
Seasonality of vitamin D level is well known. In northern latitudes (>=45th parallel) the nadir occurs around March-April, and the peak is measured on average in September-October. The timing of these fluctuations appears quite congruent with the article's assertions about life expectancy, so it's reasonable to think there is a connection.
For anyone interested in vitamin D, I highly recommend this excellent review: http://www.tandfonline.com/doi/full/10.4161/derm.24494
[+] [-] ekianjo|11 years ago|reply
[+] [-] joe_the_user|11 years ago|reply
I assume that if they are getting a meaningful correlation, it is over a large amount of data. It seems logical that at large scale, date born would correlate with a variety of things in various areas - social class and wealth come to mind.
I think it's a matter of taste whether one says "wow, throw enough data together you find unexpected correlations" or "garbage in, garbage out". A life insurance company could eek out a bit of profit changing its price structure on this data - if it didn't have far more to lose if the use of such tactics became public.
I bet someone can use this to claim astrology has validity too.
[+] [-] mbq|11 years ago|reply
[+] [-] awjr|11 years ago|reply
My hypothesis is that the age cut off in schools, unduly puts stress on the younger children in a class, that long term, impact on health in later years. In effect which month you are born in affects the stress you will feel during your school years as it will be inherently 'harder' for you.
[+] [-] kevinmchugh|11 years ago|reply
https://news.ycombinator.com/item?id=6421473
[+] [-] beaumartinez|11 years ago|reply
Others who coasted through—whom were used to everything being relatively easier—will not have the experience she has already accrued when faced with a harder challenge.
[+] [-] randomsearch|11 years ago|reply
For this to be an accurate explanation, given their data, schools in the southern hemisphere would have to start school six months later. Do they?
Your question is interesting nonetheless.
[+] [-] tomp|11 years ago|reply
[+] [-] EGreg|11 years ago|reply
[+] [-] danielbarla|11 years ago|reply
Later on I switched to a southern-hemisphere school, which was out of phase by 6 months, and I was all of a sudden roughly average age in class. Not that it had a huge impact on me, but it was noticeable, which probably means it has some effect on average.
[+] [-] TorKlingberg|11 years ago|reply
[+] [-] jcampbell1|11 years ago|reply
I wondered if they considered if the cause is age when starting school. I know that birth month has pretty powerful effects for educational attainment.
[+] [-] sillysaurus3|11 years ago|reply
I'm only half joking.
[+] [-] wobbleblob|11 years ago|reply
[+] [-] arjie|11 years ago|reply
[+] [-] dmichulke|11 years ago|reply
They touch the subject with their 3rd hypothesis but in general it's possible that you still have a higher life expectancy being born from April-June in the Northern Hemisphere because you have increased chances of reaching 50.
So why this limit of 50 years? What is the expected lifespan for newborns depending on their month of birth?
[+] [-] randyrand|11 years ago|reply
[+] [-] amelius|11 years ago|reply
[+] [-] shele|11 years ago|reply
[+] [-] FranOntanaya|11 years ago|reply
[+] [-] unknown|11 years ago|reply
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