Zinc is an important trace mineral for humans that is known to play an important role as a co-factor in a large number of enzymes and is vital to the male reproductive system. Experiments show that zinc deficiency is able to reduce the synthesis of testosterone by the Leydig cells of the testes and adequate zinc may be necessary for normal functioning of the hypothalamic-pituitary-gonadal axis, which is vital to normal male reproductive behaviour and biology. In addition, research has highlighted the importance of zinc supplementation in sperm motility in some sub-fertile males. Research published in the American Journal of Clinical Nutrition in 19921, attempted to further understand the effects of zinc in the male reproductive system by depleting male volunteers of zinc and analysing the effects on testosterone, seminal volume and sperm morphology.
The study was small with just 11 volunteers, each of which were fed an identical food formula along with a total of 10.4 mg of zinc sulphate (ZnSO4) for 28 days. Following this period the supplements were changed to contain either 1.4, 2.5, 3.4, 4.4 or 10.4 mg of zinc for 35 days, after which the subjects were tested for various markers of reproductive function. Those consuming the 1.4 mg zinc supplement showed decreased semen volumes (3.30 vs 2.24 mL) and decrease serum testosterone (26.9 vs 21.9 nmol/L). Subjects consuming the lower intakes of zinc (1.4, 2.5, 3.4) also demonstrates decreases in the total semen zinc loss per ejaculate compared to those consuming the 10.4 mg intake (6.29 vs 3.81, 4.68 and 5.03 µmol/ejaculate respectively). Subtle differences in sperm morphology were noted between high and low zinc intakes, however, low intakes of zinc did not decrease sperm motility.
The results of this study are interesting in that they show that short term changes to zinc intakes in young men can have significant effects on testosterone levels, zinc loss per ejaculate and seminal volume. This is supported by other studies that have found similar reductions in reproductive function with sub-optimal zinc intakes. The authors suggest in their conclusion that 9% of the daily intake could be lost in the ejaculate if the zinc intake is low (1.4 mg per day), but the percentage of lost zinc becomes negligible at higher zinc intakes. Factors such as calcium, phytic acid and iron can all inhibit the absorption of zinc, and intense exercise is also known to increase zinc requirement. Attaining adequate zinc in the average Western diet is problematic, and so supplementation with zinc is essential to maintain proper reproductive function in the male.
RdB
