
Lifespan depends on month of birth (2000) - Petiver
http://www.pnas.org/content/98/5/2934.full
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reasonattlm
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.

[1]: [http://longevity-science.org/](http://longevity-science.org/)

[2]: [http://longevity-science.org/Season-of-Birth.pdf](http://longevity-
science.org/Season-of-Birth.pdf)

[3]:
[http://rspb.royalsocietypublishing.org/content/282/1801/2014...](http://rspb.royalsocietypublishing.org/content/282/1801/20142032)

[4]:
[https://en.wikipedia.org/wiki/Reliability_theory_of_aging_an...](https://en.wikipedia.org/wiki/Reliability_theory_of_aging_and_longevity)

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ekianjo
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.

~~~
vlasev
I'm thinking it has to do with the continuous day/night cycle. It'll be
interesting to see if there are any changes with latitude, in particular, what
happens in countries closer to the equator.

~~~
ekianjo
But is there any rationale behind that anyway ? Do we see people born during
summer being usually in poorer health than people born during November-
December, let's say ?

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joe_the_user
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.

~~~
mbq
Also this is only about three countries selected a priori, so not a really
good sample, even if the number of individuals is huge...

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awjr
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.

~~~
beaumartinez
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.

~~~
awjr
Not sure that makes sense. She potentially experiences 12 years of increased
stress compared to her peers. I'm not implying that later in life, she will
have better tools for work, but that her body would have spent most of her
formative years under more stress.

This would then reflect in a shorter lifespan.

Note however that this concept she would gain the tools for hard working in
itself is flawed. Studies have shown that those born in the Summer months have
statistically lower exam scores.

~~~
theklub
If stress from school caused people to die earlier I think we'd know by now.

~~~
awjr
This is very hard to measure as you would be looking at teaching practices in
the 1920-1940s to determine the effects on life expectancy. I think
potentially, nationally, this would be possible as most nations have been
quite consistent on their school starting times.

I do think having a breakdown by month, not just quarter could be even more
insightful.

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EGreg
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!

~~~
danielbarla
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.

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jcampbell1
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.

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sillysaurus3
What month should I conceive my child to maximize their educational
attainment?

I'm only half joking.

~~~
jcampbell1
Depends on the rules which vary by location, but you want your kid to be the
oldest in the class. Your older kid is going to believe she is very bright in
1st grade, and have a lifetime of confidence to achieve great things. The real
reason she was such a good student in 1st grade is because she was just older.

~~~
desdiv
I know this sub-thread started in half-jest, but your response got me
thinking:

1\. Month of birth directly determines a child's age compared to their
classmates.

2\. An older child among younger peers performs better academically.

3\. Academic aptitude is correlated with income.

4\. Income is correlated with longevity.

Admittedly, hypothesis #2 is iffy. And the good old "correlation is not
causation" adage applies for #3 and #4.

~~~
saraid216
> And the good old "correlation is not causation" adage applies for #3 and #4.

It does, but it's not hard to come up with plausible causes for the
correlation to support in those cases.

It is probably more accurate to say "Academic aptitutde correlates with job
stability which correlates with lower overall stress levels which is part of
the definition for better health which correlates with longevity."

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arjie
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.

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dmichulke
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?

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randyrand
Or maybe death on the month?

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amelius
Indeed. If most deaths occur during mid-summer, then people born in autumn
live slightly longer on average than people born in spring.

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shele
"The differences in lifespan are independent of the seasonal distribution of
deaths" That's important of course.

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FranOntanaya
I would think people conceived in warm weather are more likely to be from less
stable relationships...

