March 17, 2000 (Atlanta) -- Sperm density has not changed significantly since 1950, according to a report in the March issue of Fertility and Sterility. Researchers say the findings refute the notion that exposure to environmental toxins has caused sperm quality to decline.
Because there's been considerable concern that sperm quality is declining in the U.S. and other industrialized countries, researchers collected semen specimens from 1,400 men over 36 months. The men were partners of women who were being evaluated for problems with fertility, but it was not known whether any of the infertility was due to problems with sperm. Semen, the fluid that carries the sperm, was analyzed using criteria accepted by the World Health Organization (WHO).
Approximately half the samples had at least one sperm abnormality. Flaws included problems with the sperm's swimming movement, their shape, or not having any sperm at all. The lead author says the findings are consistent with previous research.
"Our findings are very similar to a landmark study conducted in 1950," says Rebecca Sokol, MD, a professor of medicine, obstetrics and gynecology at the University of Southern California School of Medicine. "And similarity over time refutes the hypothesis that sperm quality is declining in the United States."
Previous reports about sperm quality have presented conflicting results. Some researchers have concluded that today's men are just as fertile as their grandfathers were. Others proposed that the opposite seemed to be true, while still other scientists have reported a dead heat between the generations. Observers note the discrepancy shows that larger studies are needed, using standardized methods to count the squirming little subjects.
"It's very difficult to compare sperm counts from one laboratory to the other," says Harry Fisch, MD, a urology professor at Columbia-Presbyterian Medical Center in New York. "That's why the emphasis now and in the future will be to standardize how we do semen analysis so we can have a long-ranging understanding of what's going on."
Sokol tells WebMD that her findings show there may be regional differences in sperm quality. Her results were similar to what others found with Chinese men, but differ significantly from a French study. "This suggests that there may indeed be geographic differences in sperm concentrations," says Sokol. "But overall, research shows that sperm density has changed very little in the last 50 years."
Physicians say anatomical defects and hormonal deficiencies are common causes of male infertility.
"Anatomical defects are caused by birth anomalies [defects], surgery, trauma, and infection," says Aida Shanti, MD, medical director of in vitro fertilization at the Emory Clinic and assistant professor of obstetrics and gynecology at Emory University School of Medicine in Atlanta. "And hormonal deficiencies refer to a lack of testosterone or its chemical precursors."
Shanti tells WebMD that medication can also affect sperm counts. "Blood pressure medication and steroids, including some dietary supplements used by athletes, can affect sperm counts. And there's evidence that alcohol and tobacco use may have adverse effects as well.
"The cause for half of all male infertility is not yet known, so we should continue to look closely at environmental toxins," says Shanti. "Additionally, the WHO criteria for sperm concentration has changed in recent years. So comparisons with previous studies should be adjusted accordingly."
"The most common abnormality we observed was borderline low motility [or problems with swimming movement]," says Sokol. "And time delays between collection and analysis may help explain this finding." Sokol tells WebMD that follow-up studies of geographic toxins and drug-induced effects are already under way.
- New research shows that sperm density among American men has not significantly changed since 1950.
- The finding provides evidence against the theory that environmental toxins are causing sperm counts to decline, but it cannot be completely ruled out yet.
- Anatomical defects and hormonal deficiencies are the most common known causes of male infertility, but half of all cases have an unknown cause.