Occupational heat exposure and male fertility: a review.

In humans, as in most mammals, spermatogenesis is temperature dependent. This temperature dependence has been clearly demonstrated by several experimental studies showing that artificial increases in scrotum or testicle temperature in fertile men reduce both sperm output and quality. Our knowledge of the effects of occupational heat exposure on male fertility comes mostly from a small number of epidemiological studies. We conducted an extensive review of these published reports, focusing on methodology and design (retrospective or prospective; reference group; number of subjects) and principal results (using several indicators such as the time taken to obtain a pregnancy or sperm characteristics). We concluded that occupational heat exposure is a significant risk factor for male infertility, affecting sperm morphology and resulting in delayed conception. The limits and biases involved in this type of research are also discussed.