Epidemiology and Evidence of Declining Male Fertility
Abstract
Is it is true that sperm counts are declining over time? This question may have an enormous negative impact on the popular imagination. However, this trend has been extremely hard to prove due to difficult-to-control confounding factors in the highly variable nature of seminal parameters, study population selection criteria, and apparently geographic variations in semen quality. Another crucial problem is a lack of comparability of various study populations from different time periods in secular-trend studies, due to the problems of poor quality assurance in laboratory methods for counting sperm.
Some researchers remain highly skeptical of the evidence for changes over time, whereas others argue that human sperm counts are falling and that global exposure to environmental pollutants, mainly chemicals, that act as endocrine disruptors are causing severe damage to the male reproductive tract. The biological significance of this damage over time is emphasized by a concomitant augmentation in the incidence of genitourinary abnormalities such as testicular cancer and cryptorchidism, suggesting a growing impact of factors with serious effects on male gonadal function.
Although it appears that the lifestyle changes of our societies undoubtedly play a major role in these possible trends, it seems premature, and not based on solid information, to conclude that this decline can be ascribed to social and behavioral changes alone. Such assumptions are based on few meta-analyses and retrospective studies showing a progressive decline in semen quality over time. However, other well-conducted studies could not confirm these findings, and therefore, the debate is still ongoing on whether or not sperm parameters are changing over time.