Reports on the effects of diabetes on androgen and gonadotropin secretion, testicular histology, semen quality, and fertility of men have often been contradictory, with some authors suggesting that diabetes results in severe disturbances and others reporting no detrimental effects. This discrepancy appears to be related predominantly to differences between study populations, particularly with regard to the degree of control of the diabetes of each patient and the type of treatment that the subjects received. Recent reports have suggested that the function of the hypothalamic— pituitary—testicular axis remains normal or is only very mildly affected in patients with well controlled diabetes, while suppression of gonadotropin and androgen secretion and testicular lesions occur in patients with improperly controlled diabetes. This conclusion is supported by studies in laboratory animals demonstrating that disturbances of pituitary and testicular function in diabetic animals increase in severity with the duration and degree of hyperglycemia. Thus, the question of the possible effect of diabetes on the hypothalamic—pituitary—testicular axis in man needs to be re-evaluated in properly designed and controlled studies.

Although several reports have been published suggesting the association of diabetes in man with compromised spermatozoal motility, this is also controversial; the mechanisms by which diabetes could result in this disturbance remain to be elucidated.

Finally, it is important to emphasize that the incidence of undiagnosed diabetes in patients with compromised semen quality is very low. Thus, this reviewer agrees with Spellacy et al (1979) that routine evaluation of the carbohydrate metabolic status of every patient with abnormal semen analysis is probably not cost effective.