“Caffeine is the most frequently self-administered drug in use worldwide today,” says James Bibb, an assistant professor of psychiatry at UT Southwestern Medical Centre in Dallas, Texas. Bibb is one of the authors of a study, just published in the science journal Nature, which shows that coffee affects the brain in a similar way to cocaine.

According to Bibb and his colleagues, the caffeine in coffee blocks a protein found in the brain called DARPP-32, which has been known to play a role in drug addiction. Altering this biochemical pathway prolongs and intensifies the effects of low doses of caffeine. Despite this study, “we know little about how caffeine works in the brain, whether with the kick from a double espresso or small jolts from tea or cola”, says Bibb.

We have been drinking coffee for at least 3,000 years, beginning with a dark and bitter brew from the raw berries; now our choice extends to skinny lattes, caramel macchiatos and frappuccinos, as well as the standard flat black and long white. The average American drinks 4kg of coffee a year — nothing compared with the Scandinavians, whose consumption exceeds 12kg a person annually. But as our coffee consumption increases, the messages we are receiving about coffee become more perplexing.

One of the main areas of confusion concerns caffeine — a cup of coffee contains between 30mg and 120mg. The drug is also found in tea and some fizzy drinks, such as Coca-Cola and, although caffeine is said to heighten mental performance, it can also raise blood pressure. Coffee also contains more than 800 compounds, and new research suggests that they may protect us from cancer.

Is coffee good for you?

Yes — but in moderation. “In general, there are not very many good studies which show the negative effects of coffee,” says Dr Peter Martin, Professor of Psychiatry and Pharmacology and director of the department for addiction medicine at Vanderbilt University Medical Centre, in Nashville, Tennessee. “What people are studying is the effect of caffeine, not coffee. Coffee is much more than a tablet of caffeine.”

Our count of the number of aromatic compounds in coffee has reached 800 and is still increasing, as analytical methods become more accurate. The furans are the most predominant group of compounds and these have caramel-like odours; the second-largest group, the pyrazines, contribute to the toasted flavours. But what Martin and his colleague, Dr James May, are interested in are chlorogenic acids. Vanderbilt University has recently been awarded a grant to create the Institute for Coffee Research and one of the first studies that has been carried out is on antioxidants in coffee.

Roasting coffee oxidises chlorogenic acid, which is broken down in the body to form dihydrocaffeic acid. This compound is an antioxidant and May has proved that it is preferentially taken up the body’s cells. Antioxidants can help us to live longer in a healthier state and may be found in concentrations four times higher in coffee than in tea, so drinking coffee (in moderation) does appear to be good for you.

Does coffee increase the risk of a heart attack?

Maybe. Scientists from Duke University Medical Centre in Durham, North Carolina, say that four to five cups of coffee in the morning contribute to elevated blood pressure and higher levels of stress hormones that last well into the evening. On average, the stress hormone adrenalin increases by 32 per cent.

Dr James Lane, who prepared the results of the study, says: “Moderate caffeine consumption makes a person react like he or she is having a very stressful day. If you combine the effects of real stress with the artificial boost in stress hormones from caffeine, then you have compounded the effects considerably.” This increase in blood pressure, even though slight, can be clinically significant, as it is associated with an increased risk of a stroke or coronary heart disease.

The risk of heart disease can also be increased by substances other than caffeine, such as terpenoids — which are partially removed from coffee only when it is filtered — which contribute to an increased level of cholesterol. However, Dr Collette Kelly, of the British Nutrition Institute, says: “There is not enough research to say, hand on heart, that coffee increases the risk of a heart attack.”

Does coffee cause cancer?

No — possibly the contrary. In 1997 the American Institute of Cancer Research, in Washington and the World Cancer Research Fund in London published a comprehensive review which concluded that coffee was not carcinogenic.

Indeed, coffee may help to prevent cancer of the colon. An analysis of 17 studies on colorectal cancer and coffee dating from 1960 to 1990 indicated that the risk was lowered by 24 per cent among those who drank four cups of coffee a day. In other words, coffee does not appear to be responsible for cancer, and may even confer some protective benefit.

Is it safe to drink coffee during pregnancy?

Yes, in moderation. Researchers at the National Institute of Child Health and Human Development (NICHD), in Bethesda, Maryland, warn that four cups of coffee a day double the risk of miscarriage. Caffeine can also cross the foetal blood-brain barrier and can cause seizures in new-born babies.

This damaging effect of caffeine has been witnessed in animals, leading the American Food and Drug Administration (FDA) to recommend that pregnant women limit their coffee intake. One to two cups of coffee a day seems acceptable for pregnant women, says the NICHD.

Can coffee prevent Alzheimer’s disease?

Yes. Recent research from the Faculty of Medicine in Lisbon has shown that coffee can reduce the risk of contracting Alzheimer’s disease. The study compared 54 Alzheimer’s sufferers with 54 who had not contracted the disease, matched for age and sex. They found that people who did not have Alzheimer’s had been drinking nearly 200mg of caffeine a day for 20 years — that’s just over two cups of brewed coffee a day. There is also evidence to suggest that it can reduce the risk of contracting Parkinson’s disease.

Is coffee really a stimulant?

Yes. The caffeine in coffee can increase mental alertness, according to Professor Ian Hindmarch, from the Medical Research Centre at the University of Sussex.

In one study, he and his colleagues gave 30 volunteers one to two cups of tea and coffee four times a day. Hindmarch found that repeated doses of caffeine increased cognitive performance throughout the day and although coffee had more effect than tea, it disrupted sleep more.

Psychologists at the University of Bristol have also shown that coffee reduces the malaise we feel when we have a cold because it enhances mental alertness.

Can coffee enhance athletic performance?

Yes — especially for occasional tipplers. There is substantial evidence to indicate that the caffeine in coffee increases athletic performance.

For example, in 1992 a team of researchers from the Sport Science Department at Canterbury Christ Church University College showed that coffee given to middle-distance athletes decreased the time it took them to run 1,500m and increased the speed at which they were able to run a final one-minute sprint.

This year, physiologists from Canada’s Defence Research and Development establishment proved that caffeine improves time to exhaustion, increases heart rate and boosts oxygen consumption during exercise. However, people unaccustomed to drinking coffee receive the greatest benefit.

How many cups should we drink a day?

Moderation rules. “You have to know your body and know how much you’re comfortable with,” says Martin. “Ultimately, moderate amounts — two to four cups a day — won’t harm you and may be beneficial.”

Kelly says that we should not worry about our coffee consumption. “It depends on the strength of the caffeine in the coffee,” she says, “but up to four cups of coffee a day should be OK.” Martin adds a warning caveat: “Most people drink their coffee loaded with milk and sugar and you have to ask yourself, can you afford those calories?”

Is filter coffee better for you than instant coffee?

Psychologically, yes. Blending, roasting and brewing all contribute to coffee’s complex chemical composition. For example, brewing creates hundreds of compounds. Each one weighs less than 0.3 per cent of the dry weight of the coffee but may still contribute significantly to coffee’s effects, and may act in tandem to enhance the bean’s health benefits.

Most instant coffee is prepared by freeze-drying and, as a result, many of these compounds will be retained. “My sense is that there is no appreciable difference between instant and brewed coffee if they are in similar concentration,” says Martin. However, decaffeinated instant coffee has between 30-50 per cent fewer compounds than filtered or caffeinated instant.

Hindmarch points out: “Instant coffee doesn’t have the same taste as brewed coffee and the taste can add a lot to the psychological effect. Drinking instant coffee is not like sitting down and having a latte.” He adds that some of coffee’s properties can be attributed to psychology. “We wouldn’t say: ‘Let’s go to the bar and have a caffeine pill’,” he says, concluding that coffee’s taste and its preparation all contribute to how we react to our daily brew.

How much caffeine is in a cup?

The amount of caffeine in any single serving of coffee depends on the variety of bean, where it was grown, and how it was roasted ground, and brewed.

Full-bodied, dark-roast coffee may contain less caffeine than coffee made from milder, lightly roasted beans. In general, arabica beans tend to have less caffeine and taste milder than robusta beans.