Lifespan depends on month of birth (2000)

http://www.pnas.org/content/98/5/2934.full

by Petiver • 11 years ago

116 55 11 years ago

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/

[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...

ekianjo4• 11 years ago

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• 11 years ago

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.

jrapdx3• 11 years ago

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.

For anyone interested in vitamin D, I highly recommend this excellent review: http://www.tandfonline.com/doi/full/10.4161/derm.24494

jcampbell12• 11 years ago

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.

sillysaurus3• 11 years ago

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

I'm only half joking.

jcampbell12• 11 years ago

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.

Smirnoff• 11 years ago

Purely speculative but people whom I know to be the most successful in education and career happen to be born between November and January.

Age doesn't matter though. Some of them jumped a few years ahead of their classmates so they surely weren't the oldest in their classes.

My mother did think that being the oldest helps (or as she would put it: "School and work can wait. Enjoy your childhood while you can"), so my brother and I weren't allowed to go to school until we were 8. We graduated from high school at the age of 19 & 20. Both of us had 4.0 GPA and landed full rides in foreign universities and became the first generation of college educated people in the last 4 generations that we could trace back

ggreer• 11 years ago

You'll probably enjoy The Biodeterminist's Guide to Parenting[1] by Scott Alexander[2]. It's a good overview of environmental effects on cognition. There's a section on birth month, and the answer is: It's a trade-off. If you're sending your child to public school, August is best. This makes them the oldest in their grade, giving them advantages that compound throughout school. For private school, February/March might be best, as winter babies have slightly higher intelligence and social skills.

1. http://squid314.livejournal.com/346391.html

2. You may have heard of him. Scott is a resident psychologist and writer of Slate Star Codex (http://slatestarcodex.com/).

peteretep• 11 years ago

    > What month should I conceive my child to maximize their
    > educational attainment? I'm only half joking.

I'm married to a primary school teacher. We are very definitely aiming to have babies born September to December. We aren't even slightly joking about that.

CHY872• 11 years ago

You want them to be born in September or October (or, more generally, a month or two after the school year starts). Probably October, so that there's no chance they're born in August. They'll be more developed than their July birthday brethren at every stage of their education - it's a very easy boost. For example, exams at 16 in the UK (GCSEs) that by and large everyone takes, you'd expect 54% of autumn birthday children to get 5 grades A*-C. You'd expect 48% of the summer birthday children to achieve this. At age 11, the gap is a slightly larger 8 points in terms of percentage of children who meet expectations.

This is a nontrivial difference, which makes it a trivial decision.

https://www.gov.uk/government/uploads/system/uploads/attachm...

jakobegger• 11 years ago

If school starts in september, around christmas.

vidarh4• 11 years ago

I've mentioned elsewhere that someone did a study in Norway, comparing salary later in life to age when starting school, and found no statistically significant correlation.

This was published as part of discussion on reducing the school starting age. Basically there's very little apparent benefit - at the age most kids start school, brain development appears to be the big brake on learning speed.

darkmethod• 11 years ago

My team of five software developers were all born in December. I didn't think anything of it until I saw this post on HN.

wobbleblob• 11 years ago

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.

arjie• 11 years ago

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.

joe_the_user• 11 years ago

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• 11 years ago

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

EGreg• 11 years ago

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• 11 years ago

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.

TorKlingberg• 11 years ago

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.

shele• 11 years ago

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

randyrand• 11 years ago

Or maybe death on the month?

amelius• 11 years ago

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

dmichulke• 11 years ago

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?

awjr3• 11 years ago

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• 11 years ago

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.

awjr3• 11 years ago

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.

vidarh4• 11 years ago

I don't have a link, but there was a comparative study done on children in Norway during the debate on lowering school starting age (it was 7 years when I was at school - it's 6 years now, and there's some pressure to lower it to 5).

They compared salaries and other factors based on age at school start and found basically no statistically significant differences later in life between those who had been oldest and youngest when starting school.

They did not look at things like health or stress levels, though.

kulak• 11 years ago

Since she is used to having to work hard from a young age, she will be more successful in life.

By that logic, howabout we start our kids off one year earlier, so they'll be even more successful? Or howabout 2?

collyw• 11 years ago

Malcom Gladwell's Outsiders book basically covers this topic. Usually the ones who do best are the ones with an early head start. One example that I remember is that oldest kids in class are usually the biggest, that (generally) makes them better at sport early in life. That leads to extra coaching for sports teams, more practice and the effect snowballs.

tomp2• 11 years ago

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.

kevinmchugh• 11 years ago

The cutoff benefits the youngest students academically. They get used to working harder to catch up, and never stop working harder, apparently.

https://news.ycombinator.com/item?id=6421473

randomsearch• 11 years ago

Would be interesting to look at the 'stresses' that occur within schools

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.

FranOntanaya• 11 years ago

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

Lifespan depends on month of birth (2000)

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