Does coffee drinking pose health risks? Loaded with caffeine, coffee is a natural stimulant. Drinking too much of it can make you feel edgy, nervous and jittery. Coffee can raise your blood pressure, and caffeine is slightly addictive.
But recent research has found that moderate coffee drinking - a few cups a day - can actually have some beneficial effects, and might even reduce the risk of some serious diseases.
Dr Rob van Dam of the Harvard School of Public Health in the United States has been studying the link between coffee, both regular and decaffeinated, and diabetes.
“I think about 16 prospective studies around the world have now looked at coffee consumption in relation to Type II diabetes, and they consistently show that people who drink more coffee - we're talking about four or five cups a day - have a low risk of diabetes. We're also looking at what components of the coffee could be responsible for that.  I think so far we have very consistently seen that associations are the same for decaffeinated coffee and caffeinated coffee," he said.
Dr van Dam was among several coffee experts who spoke at an experimental biology conference in Washington recently. He said a big challenge to researchers was separating out the effect of coffee from other risk factors, such as weight, diet or exercise.
Coffee and cancer
There have also been reports over the years that coffee might cause cancer. Some two decades ago, a study suggested a link between coffee and pancreatic cancer. But Dr Lenore Arab of the University of California Medical School in  Los Angeles says hundreds of studies since then have shown that coffee drinkers are less likely to get certain types of cancer, starting with colo-rectal cancer. “There might be a 24 per cent reduction with regular and higher consumption of coffee,” she said. 
“There are also surprisingly interesting and consistent results with liver cancer, that is protective to the extent that drinking coffee regularly in Japan appears to be associated with a 50 per cent reduction, and there's a dose-response (relationship) in some of the studies.  It has gone down as far as a 70 per cent reduction in those drinking more than five cups of coffee a day.”
Not all cancers respond in the same way. Dr Arab says there are some studies indicating that a pregnant woman who drinks coffee may put her unborn child at greater risk for childhood leukemia. Coffee may also increase the risk of stomach cancer.
Part of the challenge facing researchers is quantifying coffee consumption. Blend, brewing method and strength are some variables. Espresso, for example, is quite different from filter coffee. And according to James Coughlin, a scientist and consultant to the industry, the chemistry of coffee itself is enormously complex.
“There are at least 2,000 components, individual chemical components, in coffee, which makes it difficult when we're looking at some of the positive beneficial health effects. We're trying to figure out what's in there that could be contributing to that story,” he said.
Experts say that, like so many other things, coffee should be enjoyed in moderation. Drink much more than a litre a day, they say, and you may have to balance some of coffee's benefits with a risk of irritability, nervousness, and perhaps an upset stomach.