This week: What's the buzz about green tea? Claims about its health-protecting properties are numerous. The latest is that it can help antibiotics beat a range of superbugs - and it's more than just hype.

Why is it good for you? We could fill the page listing the evidence, some from scientifically designed and peer-reviewed studies, some anecdotal. But green tea has been found to help prevent cardiovascular disease and inhibit bacterial growth, and is thought to help prevent cancer. Certain compounds in green tea seem able to benefit those with multiple sclerosis, and slow down Alzheimer's and Parkinson's.

Give us some evidence, then The results of a huge study commissioned by the Japanese government, and published in the prestigious Journal of the American Medical Association in 2006, indicated that green tea could help prevent cardiovascular disease. The research looked at the tea-drinking habits of 40,530 Japanese adults and discovered those who drank lots of green tea were less likely than those who drank only a little tea to die from cardiovascular disease, though no less likely to die of cancer.

Earlier studies were criticised on the grounds that green-tea-drinkers are a health-conscious group who are probably doing a variety of things to reduce their risks. As drinking the tea is popular in Japan among diverse groups with different lifestyles, this did not generally apply to the Japanese study, though there was some correlation between heavy tea-drinking and eating lots of fruit and vegetables. Perhaps the most interesting finding was that women who drank five cups a day had a 62% lower risk of dying from strokes than women who drank little tea (with men, the figure was a 42% decreased risk).

And boosting antibiotic effects? Pharmacists from Alexandria University in Egypt say they tested green tea in combination with antibiotics against 28 disease-causing micro-organisms. Speaking last week at the Society for General Microbiology, they claimed that, in every case, green tea enhanced the bacteria-killing activity of the antibiotics. Existing published research also shows an antibacterial benefit from green tea. A study in the Journal of Nutritional & Environmental Medicine in 2001 found that green tea extract inhibited the growth of MRSA cultures.

So what's the magic ingredient? Green tea contains high concentrations of antioxidants called catechins - compounds that mop up free radicals (molecules linked to ageing and all kinds of diseases). It is the catechins, and in particular one called EGCG, that are thought to be responsible for green tea's beneficial effects.

A study published in Cancer Research in 2005 found EGCG inhibited cancer growth and another in 2006 stated: "Green and black tea polyphenols act at numerous points regulating cancer cell growth, survival and metastasis." A study in the Journal of Neuroscience in 2005 found that, in mice, EGCG inhibited the growth of the proteins responsible for the brain plaques found in Alzheimer's disease. Note, though, that the beneficial effect of one compound in green tea doesn't mean green tea itself would necessarily have the same effect.

Should we all be drinking it? Even if some of the benefits turn out to have been overstated, that comforting, steaming mug of tea is certainly in the category marked "good for you" and has only one-quarter the caffeine of coffee. A cure for all ills? Our grandmothers wouldn't be surprised to hear it.