- Scientists analyzed 185 studies which included more than 42,000 men
- No significant declines were seen in sperm counts of men living in South America, Asia and Africa
Among these men there has been a 52% decline in sperm concentration and a 59% decline in total sperm count over a nearly 40-year period ending in 2011, the analysis, published in the journal Human Reproduction Update, said.
Scientists determine sperm count by looking at a sample of ejaculate under a microscope. For sperm concentration, they measure how many millions of sperm there are in each milliliter of fluid. Sperm count, then, is sperm concentration multiplied by the total volume of an ejaculate.
Researchers led by Dr. Hagai Levine of Hebrew University of Jerusalem examined thousands of studies and then conducted a meta-analysis of 185 studies. These included 42,935 male participants who provided semen samples between 1973 and 2011. The chosen studies were well distributed over the nearly 40 years of the study period and among 50 different countries. The analysis included information on fertility status, age, ejaculation abstinence time, semen collection method, sperm count method and geographic location at the level of continent.
Based on their analysis, the international team of researchers from Brazil, Denmark, Israel, Spain and the United States reported a decline in sperm concentration of 1.4% per year with an overall drop of 52.4% during the entire study period for men living in industrialized, Western countries. Meanwhile, total sperm count among the same group plunged 1.6% per year and 59.3% overall. By comparison, the researchers found no significant declines in the sperm counts and sperm concentrations of men living in South America, Asia and Africa.
"The extent of the decline is a heartache," said Levine. "It's hard to believe -- it's hard to believe for me."
The high proportion of men in Western countries with sperm concentrations below 40 million/ml is "particularly concerning," wrote Levine and his co-researchers, because evidence indicates that a sperm concentration below this threshold is associated with a "decreased monthly probability of conception."