Coffee is enjoyed as a drink by millions of people world-wide and has been for at least a thousand years. It contains caffeine, which is a mild stimulant, and in many people coffee drinking enhances alertness, concentration and mental and physical performance. Although it contains a wide variety of substances, it is generally accepted that caffeine is responsible for many of coffee’s physiological effects. Because caffeine influences the central nervous system in a number of ways and because a small number of people may be particularly sensitive to these effects, some people have attributed all sorts of health problems to coffee. Caffeine is not recognised as a drug of abuse and there is no evidence for caffeine dependence. Some particularly sensitive people may suffer mild symptoms of withdrawal after sudden abstention from coffee drinking. A 150 ml cup of instant coffee contains about 60mg caffeine and filter coffee contains about 85 mg. For those who like coffee but are sensitive to caffeine, the decaffeinated beverage contains only 3 mg per cup.
There is no sound evidence that modest consumption of coffee has any effects on the outcomes of pregnancy or on the wellbeing of the infant. In the UK, the Food Standards Agency issued guidelines for caffeine intake during pregnancy with an upper limit of 300mg/day. This figure is in line with that stated in 1999 by the EU Scientific Committee on Food who said that 'While intakes up to 300mg/day appear to be safe, the question of possible effects on pregnancy and the offspring at regular intakes above 300mg/day remains open. Despite a small negative effect on calcium balance which can easily be made up from other dietary sources there is no evidence that this is translated into any effect on bone health. It has been known for over 100 years that coffee drinking can help asthma sufferers by improving ventilatory function.
There is no evidence that coffee increases the risk of cancer of the female breast, ovary, pancreas or kidney. It is now accepted that the small increased risk of bladder cancer sometimes associated with coffee drinking is primarily caused by cigarette smoking. There is also evidence that coffee protects against colon cancer and preliminary evidence that it protects against male breast cancer.
There is no evidence that coffee increases the risk of heart disease. Moderate consumption of coffee does not increase cardiac arrhythmias. In some sensitive individuals, ingestion of coffee after a period of abstinence may cause a temporary rise in blood pressure but there is no persistent hypertensive effect in the long term. Coffee made by the Scandinavian method of boiling or by the cafetiere method may cause mild elevation of plasma cholesterol concentration in some people but instant and filter coffee have no such effects. Although coffee elevates plasma homocysteine levels this effect is not large enough to have a significant effect on the risk of heart disease.
There is no evidence that coffee promotes indigestion in the majority of people. Although coffee is known to increase heartburn this effect is not large enough to justify advising people with gastro-oesophageal reflux disease to abstain from drinking coffee. There is no evidence that coffee increases the risk of developing peptic ulcer disease. There is some evidence that coffee may protect against gallstone disease.
Caffeine is a mild diuretic but scientific studies do not support the idea that caffeinated beverages exaggerate dehydration and electrolyte loss caused by exercise. There is some evidence that coffee may protect against the development of kidney stones.
Evidence is growing that coffee might protect against the development of Parkinson’s disease and a few studies suggest that it might also protect against Alzheimer’s disease. The relationship between coffee consumption and diabetes is an area of active investigation but no clear picture has emerged so far. Available evidence suggests that coffee might also protect against liver cirrhosis.
Coffee has a much higher total in-vitro antioxidant activity than other commonly consumed beverages. This is due in part to intrinsic compounds of coffee such as chlorogenic acid, in part to compounds formed during coffee bean roasting such as melanoidins and in part to as yet unidentified compounds. It is widely believed that antioxidants protect against the development of chronic diseases including heart disease and cancer but whether the antioxidants characteristic of coffee have such effects remains to be determined