Abstract
We systematically examined the evidence of declining sperm counts and the hypothesis that an increased exposure to environmental pollutants is responsible for such decline. Search engines, including PUBMED, MEDLINE, EMBASE, BIOSIS, and Cochrane library, were used to identify epidemiologic studies published from 1985 to 2013. We concluded that there is no enough evidence to confirm a worldwide decline in sperm counts. Also, there seems to be no scientific truth of a causative role for endocrine disruptors in the temporal decline of sperm production. Such assumptions are based on few meta-analyses and retrospective studies, while other well-conducted researches could not confirm these findings. We acknowledge that difficult-to-control confounding factors in the highly variable nature of semen, selection criteria, and comparability of populations from different time periods in secular-trend studies, the quality of laboratory methods for counting sperm, and apparently geographic variations in semen quality are the main issues that complicate the interpretation of the available evidence. Owing to the importance of this subject and the uncertainties still prevailing, there is a need not only for continuing monitoring of semen quality, reproductive hormones, and xenobiotics, but also for a better definition of fecundity.
Highlights
Carlsen and colleagues, in 1992, were the first to show robust evidence towards a semen quality decline
It has been suggested that sperm counts are declining over the last decades and that these changes might be responsible for a possible decline in fertility rates in the industrialized world
The reported decline in semen quality is a matter of great interest because it has been associated with a trend for an increased incidence of other male disorders, including testicular cancer and cryptorchidism
Summary
In 1992, were the first to show robust evidence towards a semen quality decline. Many studies have reported a decline in sperm quality over time, others could not detect any changes [2]. There are reports suggesting that the temporal decline in human sperm counts is independent of aging [5]. These changes have not been geographically homogeneously distributed, suggesting that specific factors, presented in some areas but not in others, might be related to a decline in the semen parameters [5]. Such factors include pollution, occupational exposure to industrial agents or heavy metals, and lifestyle risk factors including smoking, caffeine intake, and alcohol. Initial and final search dates were January 1985 and February 2013
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