Experts at the European Society of Human Reproduction and Embryology annual conference in London discussed studies from several European nations with large databases and the ability to track health records. They found over the past 15 years, the sperm counts of healthy men ages 18-25 significantly decreased.
For example, a prominent study from the 1990s suggested sperm counts decreased by half over the last half-century, while a recent analysis in France found the sperm concentration of men decreased by nearly one-third between 1989-2005, the Wall Street Journal reported.
Some who subscribe to the theory that world fertility might be declining said exposure to pesticides, endocrine-disrupting chemicals like Bisphenol A found in plastics and food packaging as well as a sedentary lifestyle might contribute. However, there is increasing evidence sperm count might be influenced in childhood or in the womb, too.
However, many experts questioned the validity of those findings because there are huge variations in results by country and region and some areas such as the developing world, have not been studied at all, the Journal said.
Stefan Schlatt, director of the Center for Reproductive Medicine and Andrology at the University of Munster in Germany, said he doesn't believe there is a worldwide sperm crisis. If sperm counts decreased over time, it's unclear how many men fall into the category of sub-fertile or infertile, he said.
Men produce upward of 60 million sperm per milliliter of semen, but as long as the count is roughly greater than 40 million per ml, men are considered fertile and have the same chance of getting their partners pregnant as someone who produces a higher count. But below 20 million per ml, their ability to help conceive drops -- a problem known as sub-fertility, if they succeed at all, the Journal said.