There is now abundant evidence that sexual function declines with increasing age even though interest in sexual activity may remain. This decline in function was described by Kinsey et al. in 19488, who found a steady decrease in the frequency of coitus with increasing age. Their data of the effect of age on sexual function are shown in Fig. 1.1. These data, however, have been criticized for being obtained from a very select population. Although the data were derived by interview, their subjects were all volunteers; many were either in prison or had spent a long time away from their partners and, indeed, they included relatively few men over the age of 55 years.

1.1 Prevalence of erectile dysfunction according to age.(Data derived from Kinsey et. al. 8 )

Of later studies, the most important and reliable data come from an analysis of the Massachusetts Male Aging Study (MMAS)1. In a sample of 1290 men aged 40-70 years. 9.6% suffered from complete ED, 25.2% from moderate ED, and 17.2% from minimal difficulty. The probability of complete ED rose from 5.1% at age 40 to 15% at age 70 years. Again, this population was relatively select, consisting of only Caucasian middle class men living in cities.

With regard to the overall prevalence of ED worldwide, Aytac et al.9 have recently used data from the MMAS and UN to propose that in 1995 theft were over 152 million men in the world suffering from ED and that this figure will increase to 322 million by 2025. Loss of erectile function with increasing age is probably due to atherosclerotic disease of the penile arteries and consequent corporeal ischaemia. This may result in fibrosis and loss of smooth muscle.

Data from the MMAS have also been used to estimate the incidence of ED. The annual incidence appears to rise with increasing age, from 12.4 to 46.4 cases per 1000 man years between the ages of 40-49 and 60-69 (10).

Apart from the Massachusetts study, other reports give varying estimates of the prevalence of ED. It docs seem clear, however, that it increases with age, and that libido probably declines in parallel with the loss of erections. There is also some evidence that the rate of decline is related to the frequency of previous sexual activity, with better preservation of sexual function in men who had been more sexually active. Although it has been suggested that potency may be preserved in men with more than one sexual partner, there is little evidence to support this view.