<\/p>\n
No trend studies were performed in the first half of the 20th century, said Niels Skakkebaek, a reproduction researcher at the University of Copenhagen, but in the 1940s, fertility doctors claimed that men should have at least 60 million sperm per milliliter to be considered normal and that many had more that 100 million per milliliter.<\/p>\n
\u201cNowadays, average young men have 40-50 per milliliter,\u201d he said.<\/p>\n
Professor Skakkebaek, an author of a 1992 study that suggested chemicals play a role in the steady decline in semen quality<\/a>, has since indicated that a rise in abnormal male reproductive systems may be linked to exposures to endocrine-disrupting chemicals.<\/a><\/p>\n
\u201cWe must find out which ones are to blame for the problems with male reproduction, including male infertility and testicular cancer,\u201d Professor Skakkebaek said.<\/p>\n
The website for the Centers for Disease Control and Prevention says<\/a> the effects from low-level exposure to phthalates are unknown, but it acknowledges that some types of phthalates have affected the reproductive system of laboratory animals and that more research is needed. The agency declined to offer further comment.<\/p>\n
The National Institutes of Health<\/a> also declined to comment on the research. The American Society for Reproductive Medicine did not respond to a request for comment.<\/p>\n
The practical effects<\/h4>\n
Professor Skakkebaek pointed to Denmark and Germany as examples of how this course is playing out.<\/p>\n \u201cIn Denmark, 8 percent of all children are now born after assisted reproduction,\u201d he said. \u201cIn spite of this activity, the birthrates have for 40 years been significantly below replacement level.\u201d<\/p>\n Advertisement<\/p>\n Continue reading the main story<\/a><\/p>\n \u201cThe number of young Germans have already declined 50 percent since the 1960s,\u201d he said, adding that a similar pattern has been seen in Japan, which while not a Western country, is a developed one.<\/p>\n In the United States, he said, the fertility rate among white people is \u201cbelow the levels where the population can be sustained.\u201d<\/p>\n Data about assisted pregnancies<\/a> has been linked to women having children later in life<\/a>, and in developed nations, statistics<\/a> have shown that more women are choosing to have fewer<\/a> (or no) babies, which may also contribute to the fluctuations.<\/p>\n In the recently released research, no significant decline in sperm quality was seen in men from non-Western countries, but this segment made up only about a quarter of the results.<\/p>\n Dr. Hagai Levine, the head of the Environmental Health Track at the Hebrew University of Jerusalem, who led the team, said that one of the differences between Western and non-Western countries is that man-made chemicals like phthalates \u201cbecame widespread much earlier in time\u201d in developed nations.<\/p>\n Professor Skakkebaek said that reproductive issues among African men were less common: \u201cIt is already known that Africans have significantly lower rates of another testicular problem: testicular cancer.\u201d<\/p>\n A study published last fall that looked at samples from just over 30,600 Chinese men asserted that semen quality and sperm count in the men had declined<\/a> over a 15-year period<\/a> ending in 2015 \u2014 with the percentage of qualified donors at a Hunan clinic falling from 55.8 percent to 17.8 percent in that time. To qualify, donors need to meet acceptable semen parameters including sperm concentration, sperm motility and semen volume.<\/p>\n \u201cWe urgently need international research collaboration to detect the causes,\u201d Professor Skakkebaek said.<\/p>\n![\"\"](\"https:\/\/static01.nyt.com\/images\/2017\/08\/08\/science\/00xp-spermstudy2\/00xp-spermstudy2-master675.jpg\")
\n Credit<\/span>
\n Figure reproduced from N.E. Skakkebaek et al\/Physiological Reviews <\/span>
\n <\/figcaption><\/figure>\n![\"\"](\"https:\/\/static01.nyt.com\/images\/2017\/08\/08\/science\/00xp-spermstudy5\/00xp-spermstudy6-blog427.jpg\")
\n Credit<\/span>
\n Figure reproduced from N.E. Skakkebaek et al\/Physiological Reviews <\/span>
\n <\/figcaption><\/figure>\nNon-Western men<\/h4>\n