The quality of sperm from men in North America, Europe and Australia has declined dramatically over the past 40 years with a 52.4 percent drop in sperm concentration, according to a study published July 18.
The research — the largest and most comprehensive look at the topic, involving data from 185 studies and 42,000 men around the world between 1973 and 2011 — appears to confirm fears that male reproductive health may be declining.
While a number of previous studies found that sperm counts and quality have been declining, some have dismissed or criticized the studies for things like the age of the men included, the size of the study and other aspects of the selection of the study population.
Shanna H. Swan, one of the authors of the new study published in the Human Reproduction Update, said she hoped this broad meta-analysis of all the published literature out there would put some of the uncertainty to rest.
“It shows the decline is strong and that the decline is continuing,” Swan said.
The analysis found drops only for men in Europe, North America and Australia and not for those in South America, Asia and Africa. Swan explained that this could mean that there’s something specific to certain cultures or countries that affects sperm, but that it’s also possible that there just isn’t enough data yet to draw firm conclusions about the rest of the world. There have been far fewer sperm studies conducted in non-Western countries.
The most important data points in the study involved sperm concentrations for what are known as “unselected” men who haven’t yet proven they are fertile. These are men in the studies who are on the younger side and are not yet fathers or do not have partners who are pregnant. Researchers estimated that these men had an average sperm concentration of 99 million per milliliter in 1973 but that had dropped to an average 47 million per milliliter in 2011.
That is a disturbing number given that, according to World Health Organization criteria, men with a sperm concentration of less than 40 million are considered to have an impaired chance of conceiving and those with a sperm concentration of less than 15 million per milliliter are considered infertile.
These numbers mean “surprisingly higher proportions of men are falling into the infertile and subfertile categories,” Swan said.
There are numerous theories about what may be happening to sperm. Many scientists say the most sensitive period may be during the first trimester, when the developing fetus’s reproductive system may be impacted by a mother smoking or stress she experienced or food she ate. Exposure to chemicals that can change hormone levels, known as endocrine disrupters, are among the issues being studied.
