Over the years, a number of studies have found evidence that reproductive health in men has been declining. Research has shown that sperm concentrations (SC) and total sperm counts (TSC) are decreasing significantly in several parts of the world. But there has been criticism that the investigations have focused only on data collected in North America, Europe, and Australia between 1981 and 2013. Now, the research has been updated to include Asia, Africa, and South and Central America, as well as more recent counts. This work confirmed that the decline in sperm count is accelerating, and it's happening around the world. Sperm counts appear to have been cut in half over the past four decades, and scientists don't know why it's happening.
Sperm counts are falling by about 1.1 percent every year, and SC in men who are not infertile has dropped by over 51 percent from about 101 million sperm per milliliter of semen to 49 million. The World Health Organization (WHO) considers counts between 15 million and 200 million sperm per milliliter to be normal, so even with the decline, men are still generally in the normal range.
This data included samples from 57,000 men who participated in 223 studies conducted in 53 countries. It was reported in Human Reproduction Update.
The study authors are stressing that more research needs to be conducted to find out why this is happening and to stop further degradation of sperm quality.
Sperm movement can also influence fertility, but that factor was not considered in this research.
Many things, including exposure to drugs, smoking, medication, pollution, plastics, or lifestyle factors like obesity or a poor diet might all be contributing to these observations. But researchers have not been able to link any one thing to the decline in sperm quality.
The AFP spoke to several scientists who held differing opinions about the paper, however. Some thought that we've gotten better at counting sperm, so the numbers are more accurate now and we are just getting a better picture of real sperm counts. Others think that the findings are too consistent to be ignored.