Sperm Density Virtually Unchanged in 50 Years
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."