Occupational Lifestyle Effects on Scrotal Temperature

Another situation in which occupational effects on male reproductive function might become apparent is if the occupational effect applies to a large proportion of men. It is possible that scrotal heating may be one such example. Scrotal, and therefore testicular, temperature has to be maintained some 3-4°C lower than core body temperature if normal spermatogenesis is to occur (see Fig. 2), and interference with the normal scrotal cooling process can profoundly affect sperm production, quality, and fertility (45,46). Interference with scrotal cooling is an effective male contraceptive (47). Therefore, in theory, occupational or lifestyle factors that interfere with scrotal cooling/thermoregu-lation could be significant factors in lowering sperm counts (48). Examples of such potential factors are exposure to radiant heat, wearing of tight trousers/underwear, time spent having hot baths, and time spent seated (see Fig. 2). Most of the older studies that sought to investigate such factors could rely only on establishing whether there was a

Febrile

Scrotal Hyperthermia

Fig. 2. Schematic diagram to illustrate the central mechanisms involved in cooling of the testis, and the various occupational or lifestyle factors that can interfere with their function. The primary mechanism of cooling the testis is by heat loss from the scrotum, and this necessitates air flow around it. The resulting cooling of the testis means that testicular venous blood is also cool when it leaves the testis and this blood is used to cool incoming warm arterial blood within the pampiniform plexus via heat exchange and via the diversion of approx 40% of incoming arterial blood into the testicular vein via numerous arteriovenous anastomoses; the presence of a varicocele may interfere with heat exchange within the pampiniform plexus. (For further details see ref. 69.)

Radiant heat

Fig. 2. Schematic diagram to illustrate the central mechanisms involved in cooling of the testis, and the various occupational or lifestyle factors that can interfere with their function. The primary mechanism of cooling the testis is by heat loss from the scrotum, and this necessitates air flow around it. The resulting cooling of the testis means that testicular venous blood is also cool when it leaves the testis and this blood is used to cool incoming warm arterial blood within the pampiniform plexus via heat exchange and via the diversion of approx 40% of incoming arterial blood into the testicular vein via numerous arteriovenous anastomoses; the presence of a varicocele may interfere with heat exchange within the pampiniform plexus. (For further details see ref. 69.)

relationship between such factors and poor semen quality, and, perhaps not surprisingly, the evidence proved equivocal or only marginally convincing in most cases (12). However, epidemiological studies did show that occupations involving prolonged sitting and, thus, reduction in air flow around the scrotum (45,48) were associated with significant reductions in sperm counts. An example is car or taxi driving (49,50), although away from occupational situations, the worst case is probably paraplegic men who are confined to wheelchairs (51).

More objective studies became possible once the technical problems relating to measurement of changes in scrotal temperature had been overcome, which enabled quantification of scrotal heating. Scrotal temperature was measured continuously in normal young men or in men from couples planning their first pregnancy, and a significant relationship between average daily scrotal temperature and sperm counts was established (52). Moreover, the same studies linked scrotal temperature to the amount of time spent seated, i.e., the more sedentary the lifestyle/occupation, the higher the average scrotal temperature, and this has been confirmed in more extensive recent studies (53). Application of continuous scrotal temperature monitoring in reasonably large numbers of healthy men has demonstrated unequivocally that increase in average scro-tal temperature is clearly linked to lower sperm counts, as well as to associated changes in blood levels of follicle-stimulating hormone (FSH) and inhibin-B (52-54). Such findings raised the expectation that our increasingly sedentary lifestyles in the West might induce negative effects on semen quality in a high proportion of men (12), but this expectation is proving to be overly simplistic. For example, although time spent seated is an important determinant of scrotal temperature, the former has only a weak relationship with semen quality (54), and other factors, such as nighttime scrotal temperature (53) and genetic determinants of scrotal temperature (55) may prove to be more important.

From a clinical perspective, the number of men in whom infertility is induced partly or totally by elevated scrotal temperature is likely to be low. However, there are three other points to keep in mind. First, even quite mild elevations in scrotal temperature in animal studies can increase miscarriage rates (46), so its effects on sperm can be qualitative as well as quantitative. Second, treatment to lower overall scrotal temperature in patients who have poor semen quality, although being a shot in the dark, is relatively noninvasive and can be quite effective in some cases (56)—and there are no side effects! The discovery that there are genetic determinants of scrotal temperature (55) also reinforces the possibility that some individuals may be predisposed to adverse effects of prolonged seating or radiant heat on semen quality. Although such individuals cannot yet be recognized, careful attention to lifestyle factors to minimize scrotal heating in all men with fertility problems is therapeutically benign and can have only beneficial effects. Third, the well-established, if inconsistent, effect of a varicocele on semen quality in men may itself induce such effects by interfering with normal cooling of incoming arterial blood in the pampiniform plexus (see Fig. 2), and it is possible that such an effect might be exacerbated by the time spent seated or make such individuals more susceptible to effects of radiant heat than men without a varicocele.

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