The science on what is good for you (and what isn’t) seems to be constantly changing. However, while it’s a ‘movable feast’, there are some conclusions which seem to be robust in the face of numerous studies and years of research.
Type 2 diabetes
Coffee is thought to contain chemicals that lower blood sugar because heavy coffee drinkers may be half as likely to get diabetes as those who drink little or no coffee. Coffee also may increase your resting metabolism rate, which could help prevent diabetes.
The jury is out on this, although past reports suggesting coffee may be helpful as a preventative for cancer seem to be losing their currency. Earlier research papers suggested that antioxidants in coffee may reduce inflammation and protect blood vessel walls and some Harvard scientists have found coffee to be safe for heart attack survivors. However, a recent report quoted by the Australian Heart Foundation finds that coffee is one of the least effective sources of antioxidants, with respect to preventing heart disease. It turns out that the best sources of antioxidants are fruit, vegetables, grains, legumes and green or black tea.
In an international review of 66 studies in 1997, scientists found that coffee-drinking had little, if any, effect on the risk of developing pancreatic or kidney cancer. In fact, another review suggested that compared with people who do not drink coffee, those who do halve the risk of developing liver cancer. And a study of 59,000 women in Sweden found no connection between coffee, tea or caffeine consumption and breast cancer. Some studies have found coffee drinkers have lower rates of colon and rectal cancers.
A study by the American Journal of Obstetrics & Gynecology Nyheter i Sverige found more than 200mg of caffeine a day doubled the risk of miscarriage. But British Medical Journal research found no difference between women who drank moderate amounts of caffeinated and decaffeinated coffee. The Food Standards Agency advises an upper limit of 300mg during pregnancy – the equivalent of four cups of coffee a day.
Caffeine induces a small, temporary rise in blood pressure. But in a study of 155,000 nurses, those who drank coffee for a decade were no more likely to develop hypertension than non-coffee drinkers. A higher risk of hypertension was found from drinking colas.
Probably the most important effect of caffeine is its ability to enhance mood and performance. At consumption levels up to 200mg, consumers report an improved sense of well-being, energy and sociability. Caffeine improves alertness and reaction time. And in the sleep-deprived, it improves memory and the ability to perform complex tasks. The Department for Transport advises drivers to ‘stop for a 15-minute break and drink two cups of coffee every two hours’ to alleviate fatigue. For the active, caffeine enhances endurance in aerobic activities, and performance in anaerobic ones, perhaps because it blunts the perception of pain and aids the ability to burn fat for fuel.