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IT’S PARTY night and the lads are on the razz. They’ve all knocked back a drink or ten, and now they’re slavering over anything in a skirt. What mysterious process is going on in their brains that makes them equate a capacity to consume alcohol with being a man? The same, perhaps, that makes them believe that beery breath and slurred speech guarantees their success with the woman they fancy.

Far be it from me, a mere woman, to probe the male psyche too deeply. But perhaps it is time the average man in the pub, or in front of the TV nursing a sixpack, realised what any woman down the centuries could have told him: when it comes to virility, alcohol is a guy’s worst enemy. Drinking too much of it can put paid to their lust or, if they still feel the heat, to its gratification.

Worse, prolonged boozing can actually eat away at a man’s body, leaving his wedding tackle withered, his muscles punier and his bones weaker. He may also find himself becoming less of a lad and more of a lady, as his chest sprouts breasts, his hips become more curvaceous and his chin gets smoother.

“That may be the fate of an alcoholic, but not me-Mr Moderation, the harmless social drinker,” I hear you say. But lest you become too complacent, read on.

Just a few drinks can make most men see Cindy Crawford in any woman. Some, however, find that an evening propping up the bar leaves them more interested in drinking songs than sex. Even one alcoholic binge could be enough to dampen a man’s passion, while very heavy drinkers often experience a total loss of libido. The main reason is that alcohol lowers levels of the “male” sex hormone testosterone in the blood, and one of testosterone’s many jobs in a man is to maintain and regulate the sex drive.

Levels of this hormone can fall after both a one-off binge and long-term alcohol exposure, according to Mary Ann Emanuele of Loyola University Stritch School of Medicine in Illinois. Alcohol works on the testes in different ways, by directly suppressing the testicular cells that make and release testosterone, and by increasing the levels of some hormones that inhibit these cells.

Some men, it’s true, are still randy after a heavy drinking session; but even they shouldn’t assume all will be well. One night’s overindulgence can lead to embarrassment in bed, as the ancient Greeks were well aware: they banned alcohol consumption on wedding days. The spirit may be willing, but the flesh can be disconcertingly weak, or as the porter in Macbeth had it: “[Drink] provokes the desire, but it takes away the performance…it makes him and it mars him; it sets him on and it takes him off; it persuades him and disheartens him; makes him stand to and not stand to; in conclusion, equivocates him in a sleep and, giving him the lie, leaves him.”

Brewer’s droop, as the phenomenon is known, happens because alcohol not only reduces the testosterone available for an erection, but also interferes with the nerve impulses that make it happen. In an erection, impulses from the brain and local nerves cause tiny muscles in the penis to relax, allowing blood to flow rapidly into two chambers running the length of the penis, so making it expand. “Alcohol acts directly on the nervous system,” says David Schwartz, an adviser for the Impotence World Association. “Acute high levels can decrease conduction in the nerves required for erection. This is reversible and lasts only when blood [alcohol] levels are high.”

If overindulgence becomes a habit, a man can permanently damage his virility. “Alcohol affects both the peripheral and central nervous systems-probably through the toxic effects of alcohol’s breakdown product, acetaldehyde-and can lead to erectile dysfunction and impotence,” says Michael Wilks of the Medical Council for Alcoholism in London. A high alcohol intake over five to ten years can cause an inflammation of the nerves and eventually impotence, which persists even if the man goes on the wagon, adds Schwartz.

But alcohol may do more than cause droop, whether occasional or permanent. It can also actually diminish the size of a man’s genitalia. Heavy drinking can damage the testes, says Ernest Abel of Wayne State University, Detroit, who defines a heavy drinker as anyone who consumes more than five drinks (75 millilitres of alcohol) a session twice or more a week. One study of alcoholics found that half showed some signs of shrinking testes, according to Timothy Peters of King’s College London.

Sperm decline

This is partly because affected testes make fewer sperm cells, which ordinarily occupy 95 per cent of testicular volume. There is good news, however: moderate drinkers are unlikely to suffer shrinkage, and studies suggest that for some chronic drinkers, the testes can recover even after prolonged suppression.

But research from Finland shows that even moderate alcohol consumption can decrease sperm production, which could lead to reduced fertility. Pekka Karhunen of the University of Tampere and Jarkko Pajarinen of the University of Helsinki classed moderate drinkers as men who consumed between 50 and 100 millilitres of alcohol a day (that’s up to 5 pints of beer). They found that some of these men had some sperm that stopped developing early in its three-month life cycle.

Unsurprisingly, heavy drinkers in the study fared much worse. Sperm production and growth-spermatogenesis-ceased completely in a fifth of men who drank more than 200 millilitres of alcohol per day (the equivalent of 10 pints) for at least a year.

The Finns have also found that moderate alcohol intake may alter the shape and structure of sperm. This suggests that alcohol reduces a sperm’s capacity to fertilise an egg. Laboratory experiments show that alcohol can interfere with the enzymes on the tip of the sperm which are involved in egg fertilisation. And studies on alcoholics have found that 45 per cent had abnormal sperm shapes and half had altered sperm motility.

The precise effect of alcohol on sperm is still unclear, though. One possibility is that it inhibits the metabolism of vitamin A, which is essential for sperm development. Another is that it damages some of the proteins needed to produce sperm cells.

It is very difficult to estimate how much alcohol men can drink without it affecting sperm production. “According to our as yet unpublished data, it seems to be slightly more harmful to drink small amounts of alcohol every day, than to drink more seldom, but larger amounts of alcohol,” says Karhunen.

So much for the effects of booze on a man’s bits. What about the rest of his body? While the only muscles some men flex are the ones that get glass to lip, brawnier blokes should beware of drinking too much. Muddy Saturday afternoons spent playing football on the pitch or softball in the park may do wonders for a manly physique, but follow that with 15 pints or a couple of sixpacks and you could undo the gains.

Heavy drinking can eat away at muscles, making them smaller and weaker. Muscle wasting, or alcoholic myopathy, is a slow, insidious condition that can affect drinkers who regularly consume 1000 millilitres of alcohol-the equivalent of 50 pints of beer-a week, according Peters.

Tired old drunk

Alcoholic myopathy affects the muscle fibres involved in short bursts of movement, such as those in the buttocks, thighs and shoulders. Sufferers tire easily on exertion, may find it hard to rise out of a chair or climb stairs, or may find themselves unsteady on their feet, or developing backache. Researchers think alcohol interferes with the machinery of protein synthesis so that the muscle cannot repair itself. Remarkably, Peters has found that staying on the wagon for between three and six months is enough to reverse muscle wasting, although other researchers report that muscle strength is never fully regained.

Although chronic drinkers are most at risk from myopathy, binge drinking can also affect muscles. Peters says that bingers can develop a rare condition that results in tender, swollen muscles, often in the calf, and that may eventually lead to kidney damage. This myopathy causes the muscle fibres to swell, then burst and die.

Drinkers can also develop weaker bones. “Men who experience testosterone deprivation for any reason throughout their life have decreased bone mass,” says Emanuele. Calcium determines the strength and stiffness of bone, and alcohol alters the way it is absorbed, excreted and distributed throughout the body. Acute alcohol consumption-that is, one night’s heavy drinking-can trigger the body to excrete more calcium in the urine, while chronic heavy drinking can mean that the body does not absorb enough calcium from food. Some studies of alcoholics have found that alcohol is toxic to bone-forming cells and inhibits their activity.

Then there are the changes that, while seemingly more cosmetic, may be equally disturbing. Men who regularly drink large amounts may grow breasts and develop hips, as fat shifts from the abdomen. The reason for this bizarre development is down to hormones again: alcohol can upset the delicate balance between testosterone and the “female” hormone oestrogen. In fact, men and women have both hormones, but testosterone levels are normally higher in men. Alcohol appears to speed up the normal conversion of testosterone and one of its precursors, androstenedione, into oestrogens, explains Emanuele, possibly by stimulating the enzyme involved in this conversion.

Feminine side

Schwartz offers another reason for this apparent feminisation. “The liver metabolises testosterone and oestrogen,” he says. “If the liver is impaired as a result of long-term alcohol use, oestrogen is not removed from the blood and levels rise, which in turn suppresses testosterone.”

Yet another possible explanation for rising oestrogen levels is that some alcoholic drinks contain oestrogen-like substances. These phyto-oestrogens, which originate in the plants used to make alcoholic drinks, have been identified in bourbon, beer and wine.

Some alcoholic men may discover even more of their feminine side. They may find they don’t have to shave as much and may start to lose facial and body hair, which are maintained by the all-important testosterone. “Hair loss can result from any condition where testosterone is low,” says Emanuele.

So what’s the message for men who have a few drinks after work most nights? Should they be worried? The effects of alcohol depend on a person’s physical characteristics and genetic make-up, as well as the circumstances of consumption, but most experts seem to agree that two drinks a day is fine. There’s no evidence that moderate drinking damages the reproductive system or muscles, says Samir Zakhari, director of basic research at the National Institute on Alcohol Abuse and Alcoholism in Bethesda, Maryland.

But before you go out to celebrate this news, Zakhari has a word of warning about binge drinking. “It’s like a man who takes the subway to work every weekday but drives his car at a hundred miles an hour on a Saturday,” he says. “Revving the engine to this extent can still cause damage, even if it is only once a week.”