All women, and most men, know about the menopause. Women have a sudden lowering of estrogen levels leading to their menstrual periods stopping; this is often accompanied by hot flashes, irritability, and vaginal dryness. It is a fairly short-lived event, spread over a matter of months, and although some of the symptoms can persist much longer, they can usually be controlled by appropriate treatment.

The possibility that men might experience a similar wind down in reproductive function has been pondered for some years. In the mid-1940s a scientific paper was published describing the symptoms that men can develop in connection with a decline in levels of the male hormone testosterone; these could be reversed by testosterone injections. Such symptoms in fact only occur in a small percentage of men, and are not associated with a sudden observable change, such as the cessation of menstruation.

The British Medical Journal has just reopened discussion of the male menopause, using a debate format. Two specialists argue that there is a clear-cut condition that has symptoms that deserve to be treated, while another suggests that the gradual decline in male sex hormone levels is a natural process of aging and does not, in itself, require therapy.

Writing in favor of the existence of a male menopause, the experts refer to the testosterone blood levels that are critical for male sexual function, and point out how these decline steadily from the age of 45 or so. (The cells responsible for producing the hormonal-stimulus for testosterone formation are smaller and less numerous as we age.) In parallel with this decline in testosterone production, there is an age-related increase in the blood of a protein that fastens onto to sex hormones, which means that there are less of them available to exert their actions. Consequently, the amounts of available testosterone decrease by as much as 50% between the ages of 25 and 75. Adding to this, the daily rhythm of the pituitary gland's control can result in exaggerated falls in testosterone levels in the evening.

While hereditary factors can play a role in these events, more likely risk factors for early severe falls in testosterone levels are trauma or inflammation of the testes (e.g. after mumps), obesity, excessive alcohol intake, and diabetes. Some authorities believe that physical and psychological stress is relevant, too.

Not surprisingly, people assume there is a direct link between the fall in male sex hormone levels and the fairly common decline in sexual interest and potency reported with age. However, a close relationship is by no means certain. There are many other causes of decreased potency in elderly man - for instance, changes in blood vessels, nerves, or the effects of medication.

The symptoms of the male menopause listed in the early '40s include: depression and nervousness, flushes and sweats, decreased sex drive, inability to have or maintain an erection (erectile dysfunction), easy fatigue, poor concentration and poor memory. Reduced bone mineral density (leading to weak and brittle bones) and an increase in upper and middle body fat, that are often seen as we age, are also associated with lower blood levels of testosterone. Some studies have shown an improvement in the described symptoms, as well as an increase in bone mineral density and muscle bulk and strength, following testosterone injections.

These various pieces of information lead the "male menopause" champions to the view that the symptoms experienced by aging men can be helped by testosterone therapy, much the same way that post-menopausal women can be helped by hormone replacement therapy using estrogens.

The expert that argues against this approach points out that the links between the rather vague symptoms and decreases in average testosterone levels are not strong enough to say that one is caused by the other. To obtain evidence of this we need more conclusive studies involving testosterone replacement. In most of the studies reported to date, the doses used have been unsuitably high. When doses large enough to raise elderly men's testosterone levels to the range found in 20-year-olds were given in a study, there was no improvement in bone mineral density or muscle strength (although body fat was reduced).

In particular, it is unclear how important testosterone is in the declining sexual activity reported in elderly men. As we said earlier, as many as 80% of cases of erectile dysfunction are thought to have a medical cause, such as diabetes, blood vessel disease (atherosclerosis), nerve disorders (multiple sclerosis, spinal injury), surgery (prostatectomy) or injury. The intensity of impotence is more likely to be a function of psychological difficulties than hormonal deficiencies.

The availability of Viagra (sildenafil citrate) now allows successful treatment of many forms of erectile dysfunction. It is much safer from a benefit/risk viewpoint than injections of testosterone, which carry a fairly severe risk of liver toxicity.

The opponent of "male menopause" suggests that the other signs of sexual decline and apparent symptoms of menopause in men are more likely related to age-related changes in hormones other than testosterone, such as those from the adrenal glands or pituitary gland. Hormone replacement treatment is highly successful in diseases such as diabetes or low thyroid activity, compared with the results of testosterone in aging men.

In summary, it seems likely that the symptoms credited to the male menopause are better treated if an exact cause can be determined - whether this is a medical condition producing erectile dysfunction or a naturally aging phenomenon causing other hormonally-related conditions. Sufferers looking for more information can visit "It never ends: Aging and Sexuality".