In a peer-reviewed editorial published on October 10, 2017 in The BMJ, Niels Skakkebaek from the Department of Growth and Reproduction, Rigshospitalet, University of Copenhagen, Denmark, discussed “disturbing trends in men’s reproductive health,” and argued that chemical exposures could be one contributing factor requiring “urgent attention.”
A recent systematic review and meta-analysis found “significant declines in sperm counts” among Western world men. This study was carried out by a team of scientists from the U.S., Israel, Spain, and Denmark, and published in July 2017 the peer-reviewed journal Human Reproduction Update (FPF reported). Its results largely agree with Skakkebaek’s own findings, starting with those reported in The BMJ 25 years ago, and the findings by other groups (FPF reported).
Skakkebaek emphasized that “trend data [on the quality of semen] should be interpreted with a holistic view of male reproductive health problems, including parallel trends in testicular germ cell cancer (TGCC).” This is because the incidence of this cancer and risk of poor semen quality are known to be interlinked, he explained, supported by the fact that “strong clinical evidence exists that testicular cancer and spermatogenic disorders are biologically interrelated.” Furthermore, both types of ailments are suspected to have a fetal origin, since for example congenital cryptorchidism is a risk factor for both TGCC and poor semen quality.
Disturbingly, not only has the semen quality declined, but also the incidence of TGCC “has risen substantially over the past few decades,” Skakkebaek observed. These increases were seen “particularly in young men” and “even in countries that have had low incidence.” One hypothesis linked to both observations suggests that a “testicular dysgenesis syndrome” which affects the function of testosterone-producing Leydig cells may be involved. Indeed, a temporal trend for a reduction in the circulating levels of testosterone has been reported as well. These mechanisms have been discussed in, for example, a review by Skakkebaek and colleagues, published in 2016
“What could be causing such disturbing trends?” Skakkebaek asks rhetorically, and answer that, in short, “we do not know.” However, environmental influences, including environmental exposures to chemicals, are likely to be involved. Among these, of particular concern are the endocrine disrupting chemicals (EDCs) such as various pesticides (FPF reported) as well as several other groups of chemicals widely used in everyday consumer products (FPF reported). However, “little has been done to explore [EDC’s] potential effects on semen quality and testicular cancer,” therefore “we must act now to prioritize new basic and clinical research programs in reproductive medicine,” Skakkebaek concluded. Among the research questions that urgently need attention are “What is the role of exposure to [EDCs] in reproductive trends? … What is the role of dysgenesis of fetal testis caused by maternal exposures? Why is the incidence of testicular cancer increasing among young men of reproductive age?”
Niels Skakkebaek (October 10, 2017). “Sperm counts, testicular cancers, and the environment.” The BMJ, 359:j4517.
Levine, H., et al. (2017). “Temporal trends in sperm count: a systematic review and meta-regression analysis.” Human Reproduction Update (published July 25, 2017).
Carlsen, E., et al. (1992). “Evidence for decreasing quality of semen during past 50 years.” The BMJ, 305:609.