Has the quality of human sperm has been “going downhill” over the past century? As I’ve noted here before — and as Discover magazine points out in its November issue — much (but not all) of the evidence suggests that the answer to that question is “yes.”
Writes science reporter David H. Freedman for Discover:
Men appear to be making less sperm on average, several studies report, and what is made tends to be subfertile, which the World Health Organization describes as sperm that swim poorly, take on a funny shape, fail to reach concentrations higher than 15 million per milliliter, or otherwise struggle to impregnate an egg.
“We’re producing pretty poor sperm compared with those of primates and other mammals,” says Gary Cherr, a reproductive toxicologist at the University of California, Davis. “Even in the most fertile men, there are quality issues.” A recent European report found that one in five young men has underachieving sperm. That is probably one reason why in vitro fertilization (IVF) is becoming increasingly common, with 4 million humans worldwide already owing their existence to the procedure.
The quality of a man’s sperm tends to decrease with age, a factor that may explain why older men sometimes have difficulty becoming fathers. But that doesn’t explain why sperm appears to be getting less vigorous among young men.
What could be behind that decline? Research points to environmental toxins, but also to lifestyle factors, says Freedman:
Epidemiology studies have linked low sperm counts not only to aging but also to being too fat, being too thin, lack of exercise, excessive exercise, junk food, soda, exposure to toxins in food and air, and use of both prescription and nonprescription drugs, including tobacco and alcohol.
“I can tell much more about a man’s health by his sperm count and belly size than I can from all the blood tests men usually get at the doctor’s,” Harry Fisch, a urologist and researcher at Weill Cornell Medical College in New York City, told Freedman.
Improving the count
Fisch tells men who want to improve their sperm count to adopt healthier habits and to get off certain medications — including testosterone supplements, which, he told Freedman, shrink the testicles and inhibit sperm production.
Other treatable causes of poor sperm count, Fisch added, include infections of the urinary tract or prostate and a condition called variococeles, or “varicose veins of the testicles.”
Scientists have also found that many men today — about 25 percent, according to one study — have a mutant gene that makes their sperm less likely to survive the swim through the cervix to the egg. Men with that mutant gene are about 12 percent less likely to conceive. That’s not a lot, but it may be enough in some cases to prevent the men from becoming fathers naturally.
Blame it on monogamy?
Interestingly, reports Freedman, monogamy may also be a factor in why human sperm quality is declining:
The genes that control the sperm-making machinery are all packed into a single chromosome — the Y chromosome, the one that confers maleness. When a cell divides, chromosomes line up with similar mates such that if one chromosome is scrambled, it can use its counterpart as a template for repair.
Unfortunately, the X chromosome lacks sperm-producing genes, so the Y chromosome is unable to autocorrect. “It’s molecularly programmed to degrade over time,” says Sherman Silber, a urological surgeon and researcher who heads the Infertility Center of St. Louis at St. Luke’s Hospital.
In most species that degradation is countered by female promiscuity and intense male competition, which ensure that only the highest-quality sperm fertilize an egg and perpetuate their DNA. Human society’s precipitous rush toward monogamy and non-mortal-combat-based dating rituals have therefore been an unmitigated disaster for the Y chromosome. Sperm have let themselves go because they can.
You can read Freedman’s article on the Discover website.