The truth about your cup of coffee

So you like coffee. There you are, drinking gallons of the stuff from morning to midnight, and then suddenly it's unhealthy - yet again.

This time it's blamed for causing cancer, or is it arthritis, dementia, heart disease or epilepsy? But just as you sigh and reach for the herbal teabags, there's fresh news from the research front: coffee is actually very healthy, and lowers the risks of cancer, cirrhosis of the liver, gallstones and umpteen other diseases.

No food has generated so many conflicting research findings, and few have been investigated as often. According to the National Library of Medicine, there have now been almost 20,000 scientific studies and the number is increasing daily.

In the latest study revealed last week, researchers found that a couple of cups of coffee can be protective against Parkinson's disease. The findings add to a growing body of evidence that this may be so, although there are doubters.

In the past year alone, various researchers have found that drinking two to four cups of coffee a day can lower the risk of colon cancer (25 per cent), gallstones (45 per cent), cirrhosis of the liver (80 per cent) and Parkinson's disease (50 to 80 per cent). It can even reduce the incidence of asthma (25 per cent) because of the presence of the chemical theophylline.

Although the chemicals and anti-oxidants present in coffee do figure in some studies, the ingredient that gets the most attention from researchers, whether they find adverse or beneficial effects, is caffeine. But despite the attention it gets, little is known about how it works to bring about disease or cures.

Another mystery about caffeine and coffee research is why the results are so conflicting. Some, for example, find links between cot deaths and consumption, while others find none. Some blame coffee for heart disease, while others say it may be protective.

"One of the big difficulties with all this research is quantifying people's consumption of caffeine. It is very difficult to get accurate records of what people eat and drink at the best of times, but with caffeine it is very, very tough,'' says Dr Susan Jebb, nutrition scientist with the Medical Research Council.

"You get people to fill in dietary diaries for researchers saying how many cups they drink a day, but they may well not say whether it is fresh or instant, how big the cup is, how strong the coffee is, or whether it is decaf and so on. That makes it a very difficult job.

"Coffee also contains things other than caffeine, which may be having an effect. And if they are looking at the effects of caffeine, that too is complicated because it comes in many other foods.''

So what should coffee drinkers do? Is it healthy, or can nothing save them from herbal teabags?

"With modest consumption - three or four cups a day - there is no evidence of adverse effects,'' says Dr Jebb.

HEALTHY

Colon cancer: Risk of colon cancer is 24 per cent lower among adults who drink four or more cups a day compared with those who never drink coffee. It is thought that caffeine neutralises cancer-causing agents in the bowel.

Parkinson's: Four or more cups a day may reduce the risk of Parkinson's disease, with regular drinkers able to reduce the danger by between 50 and 80 per cent.

Allergies: Coffee can ease the symptoms of hay fever and allergic reactions, say researchers in South Korea who believe that the beneficial effects are down to caffeine's ability to limit the release of histamine when pollen and dust trigger a reaction.

Depression: Researchers say that coffee is a good anti-depressant largely because it has four times as many anti-oxidants as green tea. It is also said to improve memory levels.

UNHEALTHY

Rheumatoid arthritis: Research in Finland shows the risk increases with the number of daily cups, and those who drank 11 or more a day were almost 15 times as likely to have problems.

Miscarriage: Too much caffeine doubles the risk of having a miscarriage, according to research which found that consuming five or more cups of coffee a day significantly increased the danger of losing a baby.

Heartburn: German researchers showed that coffee consumed in large quantities in a short time can trigger reflux or heartburn. Caffeine, oils or other compounds introduced during processing could be to blame, they say.

Heart disease: Coffee drinkers have higher levels of homocysteine, a chemical linked to heart disease and stroke and which researchers have found can survive coffee filtering.