We all know that female fertility declines with age and after the onset of menopause a woman is considered to be infertile unless supplemented with hormone replacement therapy. Whether age affects fertility in males still remains a controversy. Unlike women men do not undergo a hormone induced menopause; nonetheless it is well known that there is a definite decline in sexual function of a male with increasing age.

Pathophysiology of decreasing male fertility after 50 years of age:

Erectile dysfunction: Men over the age of 50 require greater foreplay prior to get an erection. While teenage men can engage in repeated sexual activity, older men are not able to perform repeated sexual activity until hours after. The refractory period between two erections progressively increases with age. Also the turgidity of an erect penis is less in the older age group than in young males. This could be due to the progressive degeneration of the muscles which happens otherwise during the process of aging as in the other parts of the body.
Hormone levels: Various studies have proved that there is a decrease in the levels of testosterone after the age of 50 years. The decrease in the number of Leydig cells due to apoptosis and decreased regeneration may be responsible for the decrease in testosterone production. Yet it never falls below the normal range. With advanced age there is also an increase in the levels of Follicle Stimulating Hormone (FSH) and Leutinizing Hormone (LH) which negatively stimulate the testosterone levels.
Decreased spermatogenesis: A study conducted by Johnson in 1984, showed that men over the age of 50 years are likely to produce 30% less sperms than younger men. The decline in spermatogenesis is most marked in men who are oligospermic. The decreasing spermatogenesis is due to the decline in the number of seminiferous tubules producing mature spermatids.

Though a number of sperms in the early phase of maturation are likely to be present in the testes, further maturation of the sperms is arrested leading to a reduction in the number of mature sperms. This effect is most marked in males who may be at the lowest rung of fertility when young and hence become infertile after the age of 50 years.
Quality of sperms: Apart from decreased spermatogenesis, it has been shown by various studies that the quality of sperms also decreases. These sperms are likely to have damaged DNA and hence may cause genetic abnormality if conception occurs. There is also a reduction in the sperm motility as was observed by a study conducted in Berkeley at the University of California.

The results of the above study showed that there was a fall in the volume of semen by 0.03 ml per year of age, there was a decrease in motility by 0.7% every year, the forward motility decreased by 3.1% each year and the total percentage of progressively motile sperms decrease by 4.7% per year.