I can't help it, this paper made me sing.
To everything (sperm, sperm, sperm)
There is a season (sperm, sperm, sperm)
And a time, to many humans,
It's the time, of the season (wow, wow, wow)
When sperm runs high
In this tiiiime, be mindful of your sperm counts
And dare to try, with fast-swim sperm...
We know that many animals have a "season". Maybe females go into heat, or males produce more or less sperm. In sheep and goats, the "season" is so profound that males actually halve their testicle weight (I'm trying, and failing, to imagine this happening in humans).
But do humans have a season? Female fertility is more of a monthly issue, but what about men? At first, this seems like a silly question. Sperm take about 70 days to mature, and men are always producing new sperm. So you know, if it's not good, just make more! But in fact...there may be a season. And men, you're in season now.
Levitas et al. "Seasonal variations of human sperm cells among 6455 semen samples: a plasible explanation of seasonal birth patterns" American Journal of Obstetrics and Gynecology, 2013.
Did you know that fall babies are more common?
The differences look pretty small, but when you're dealing with such gigantic numbers, they still end up significant. More babies are born in the fall (as my Facebook, with its birthday alerts, constantly reminds me), with the biggest spike in November. But why is that? Is it due to variation in female fertility? Male fertility? A certain ..."feeling"... in the air around Valentine's day (hey, February, is 9 months from November. We can count)?
Well, this study says the difference might be in the sperm. The authors of this study took over 6000 samples of sperm from a bunch of male patients being given their first evaluation for infertility. When a couple can't conceive, you often screen both the male and the female first, which means that some of your men will end up normal (normozoospermic, aka normal sperm), and some will show that they have infertility issues (oligozoospermic, aka not normal sperm). But in all of them...the authors saw a season.
The differences don't look like much, I was so shocked at all the overlapping standard deviations that I plugged the data in and analyzed it myself, but this is where the numbers make the difference, and they make a big one. In both normozoospermic men and oligozoospermic men, sperm have a SEASON. You get the highest concentrations of sperm in the winter and spring, as well as the fastest moving sperm and the best morphology (nicely shaped). This was the case if you looked at the sperm by season of...um...sperm delivery, and if you looked at it by dating back 70 days to when it was produced. Men produce the best sperm during the winter and spring.
Of course, this doesn't mean that they can't produce sperm at other times, obviously we all know that's NOT a problem. But it does mean that, in men suffering from infertility, you might be able to target your infertility treatments toward the times of highest sperm production in winter and spring, to get the biggest bang for your buck (you see what I did there).
And of course, it goes to show that for everything, there is a season.
A time to make sperm,
a time to mate,
have sex now please,
before the year's too late!
Levitas, E., Lunenfeld, E., Weisz, N., Friger, M., & Har-Vardi, I. (2013). Seasonal variations of human sperm cells among 6455 semen samples: a plausible explanation of a seasonal birth pattern American Journal of Obstetrics and Gynecology DOI: 10.1016/j.ajog.2013.02.010