Health: A Question of Health: Espresso to insomnia

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I have heard that both coffee and tea have caffeine in them. Why is it only coffee that keeps me awake at night?

A cup of coffee has about 75mg of caffeine and a cup of tea has about 30mg. Cola drinks fall in between coffee and tea, with about 50mg of caffeine. Caffeine is a stimulant, and its effect, like most drugs, depends on the dose. A cup of espresso can be very effective at ruining a good night's sleep by providing a whopping 150mg of caffeine. Recent research has revealed another, unexpected effect of too much caffeine. Pregnant women who have more than 150mg of caffeine a day are more likely to miscarry than those who have less than that amount, and more likely to have a baby who will be underweight at birth.

Because of developing arthritis, I have started taking glucosamine. The recommended dose is 820mg a day. But I have heard that a dose of 1,200mg is more effective. Which is correct?

There have been at least eight scientific studies of glucosamine over the last 20 years. Most of them have used doses of 1,500mg a day. The results of these show that glucosamine appears to be beneficial in reducing pain and tenderness in arthritic joints. Some of the studies have compared glucosamine with ibuprofen (a widely used painkiller available without prescription). These have shown the two drugs to be similar in their effectiveness for arthritis symptoms. There do not seem to be many reports of serious side effects from glucosamine, but some people do experience stomach pains, heartburn, diarrhoea and nausea. One possible problem with glucosamine is that it is sold as a food supplement, rather than a licensed drug, and so it is difficult to be certain about its purity.

What effect will a vasectomy have on a man's sexual enjoyment and performance?

When a vasectomy is performed the tubes that carry sperm from the testicles to the penis are cut, so no sperm is present in a man's semen after a vasectomy. (It may take several weeks for sperm to disappear from the semen, so it is important to have several semen analyses before relying on a vasectomy for contraception.) But the absence of sperm in the semen does not interfere with sexual enjoyment or performance. Semen is mostly made up of secretions from the prostate gland and seminal vesicles, and a vasectomy does not affect these secretions. So the amount of semen that is ejaculated is not reduced and the sensations of orgasm and ejaculation are not impaired. Once the discomfort of the vasectomy operation is over, sexual performance and enjoyment should return to normal levels. Indeed, some men find that sex is better after a vasectomy because the risk of pregnancy is removed. The risk of passing on or catching sexually-transmitted diseases, however, is not affected by a vasectomy.

Please send questions to A Question of Health, The Independent, 1 Canada Square, Canary Wharf, London E14 5DL; fax 0171-293 2182; or e-mail health@independent. Dr Kavalier cannot respond personally to questions