Is Human Sperm Getting Less Healthy?
Earlier this year, my student Marya and I published “Global decline in semen quality: ignoring the developing world introduces selection bias“. The paper got the attention of writer Katharine Gammon, who interviewed me about it for her LiveScience.com article, “Sperm Quality & Quantity Declining, Mounting Evidence Suggests.”
Well, her article was picked up by the wires, and went a little viral. It’s been reproduced on NBC News and the Huffington Post.
And you know you’ve really arrived when your name occurs somewhere in the pages of Jezebel.com!
I’m particularly proud that my employer, the University of Ottawa, added the article in their official press feed:
They then asked me to blog about it for their newsletter, The Gazette, which I was happy to do.
As regular readers know, I like to keep a public record of everything I do. So I’m reproducing the Gazette post below, even though they won’t publish their version for another couple of weeks. I don’t think anyone will mind.
I welcome all comments about this curious issue.
Did you know that scientists have been collecting data on sperm quality for about seven decades? And did you also know that, according to at least one famous analysis of these data, the overall quality of sperm has been declining steadily over the years? During a recent panel discussion, a colleague leaned over and whispered to me, “What constitutes normal today wouldn’t even be on the scale a few decades ago!”
Most of these data have come from men donating to sperm banks. And most of the sperm banks are in urban centres in Western countries. This probably constitutes what we epidemiologists call, “selection bias”. It’s when the way in which the data have been selected may be affecting the conclusions we attempt to draw from such data.
For example, men who choose to donate are inherently different from men who don’t; populations with sperm banks may be inherently different from populations without them; and countries with well-organized data collection systems for their sperm banks are probably different from countries without such systems.
So, in our paper, “Global decline in semen quality: ignoring the developing world introduces selection bias”, which was published in the International Journal of General Medicine earlier this year, Marya Jaleel (a Health Sciences student) and I proposed that the global sperm data is incomplete, because it under-samples potential contributions from men in rural, poor and non-Western countries.
Men in such places probably do more physical labour than the rest of us, are less likely to eat a processed, chemical diet, and are less likely to be exposed to many environmental pollutants, in particular pollutants that may mimic human hormones.
This is important for a couple of reasons. First, if it is true that there is a global decline in sperm quality, and if that decline is not seen in poor, non-industrialized populations, then it means that the cause of any observed decline is probably related to the modern, Western lifestyle. Things like our processed diets, obesity rates, aging populations, pollution and hormonal additives to our environment may be causing our sperm to be less motile, plentiful and healthy.
And second, it’s important because any environmental impact on our reproductive systems might be pointing to some less easily seen effects on our overall health. In other words, a decline in sperm quality may be a sign of deeper biological damage.
The global industry of reproductive technologies is now worth billions of dollars, and its growth is accelerating. The issue of declining human reproductive capacity is bound to garner an increasing amount of attention and concern in coming years.
What do you think? If the decline in sperm quality is real –and it still might not be!—what do you think might be causing it?
Update #1: The story has legs! It’s been reproduced in Yahoo News, Fooyoh.com, and even Indonesian news has picked it up. The Medical Daily has plucked elements from the original news story to make their own version, even alluding to my on-the-record comments, but not citing me by name. Most interesting to me is that the American Council on Science and Health is quoting me in support for their position that man-made chemicals do not have an effect on human reproduction. The ACSH hasn’t misquoted me at all, but readers should be aware that they are funded by the chemical industry, and therefore have a financial interest in promoting scientific claims that minimize the biological impact of industrial activity.
Update #2: A community news service called Open File has now quoted me on this issue. The Oh Face blog has quoted me. And the UOttawa Gazette blog post is now live, as is my interview with the UOttawa student paper.×