The debate about the health effects of coffee drinking has been raging for the last 25 years, and like all good debates, both sides have interesting points to make, and the questions largely remain unanswered. UK coffee consumption fell by 10% between 1998 and 2003, but Brits are still the biggest consumers of instant coffee in Europe (the Finns are the biggest consumers in the world, but are fussier about their coffee and drink more ground coffee). The main active ingredients in coffee are caffeine and coffee oils.
The good bits
The main effect of caffeine on the body is as a stimulant to the central nervous system. Caffeine is associated with an increase in intellectual activity, but this only appears to be significant if the person is tired or bored. In these situations, however, it certainly makes people feel more alert and less fatigued. Coffee after lunch helps to counteract the common 'dip' in concentration. Caffeine has also been shown to be beneficial to night workers. Caffeinated coffee can also help to prevent road accidents, according to the Sleep Research Laboratory at University of Loughborough
There is strong evidence that coffee has a protective effect against the development of colon cancer, if more than four cups a day are drunk. Higher intakes may give more protection
Coffee contains anti-oxidant chemicals, and so may have a role in the prevention of heart disease and certain cancers, although these benefits are theoretical, and as yet unconfirmed
Caffeine has a beneficial affect on airways constriction in asthma sufferers, but the intake needs to be quite high to moderate an asthma attack
There is some evidence to suggest that coffee may reduce the risk of developing kidney stones and gallstones.
The bad bits
Women who drink caffeinated products lose more calcium in their urine and tend to have less dense bones than non-caffeine drinkers. This may increase the risk of osteoporosis in susceptible women. It has been suggested that women should drink at least one glass of milk a day for every two cups of coffee, to try to offset the calcium loss
Caffeine increases secretion of stomach acid, which is how it aids digestion as an after-meal drink. However, this acid-secreting property is bad news for people with acidity symptoms or stomach ulcers
Caffeine aggravates pre-menstrual breast pain in a significant number of sufferers
Caffeine can aggravate insomnia
Women who drink more than four cups of coffee a day have twice the risk of urinary incontinence compared with women who drink little or no coffee
Caffeine withdrawal can produce unpleasant headaches and shakiness
Coffee contains many carcinogens, whether or not it is decaffeinated. There is, however, no strong evidence of an increased risk of cancers in coffee drinkers
Coffee pumps up our stress hormones, and can cause palpitations, a rise in blood pressure and symptoms of anxiety.
The controversial bits
The most hotly contested issues relate to possible problems in relation to fertility and pregnancy. There have been many studies producing some conflicting evidence. The pro-coffee lobby claims that moderate caffeine consumption (up to 300mg a day) does not affect fertility, or cause adverse health effects in the mother or the child
Other researchers claim that high caffeine intake is associated with reduced fertility, increased risk of miscarriage, and low birth weight. Some studies suggest that pregnant women consuming 300mg of caffeine a day are twice as likely to miscarry, and women consuming 150-300mg are twice as likely to have a low-birth-weight baby compared with non-caffeine drinkers. These findings can be difficult to accurately attribute directly to drinking coffee, as caffeine consumption is often linked to other risk factors such as smoking and alcohol consumption. There may also be another explanation for the apparent increased miscarriage risk. It is already known that women who don't have pregnancy nausea are more likely to miscarry. Women who are nauseated are less likely to drink coffee, and this may have contributed to the impression that women who don't drink coffee are less likely to miscarry. What is known is that pregnant and lactating women metabolise caffeine more slowly than do other people. Caffeine passes across into breast milk, and babies are also slow metabolisers
The fertility issue is equally controversial. Some experts suggest that coffee increases female infertility by up to 50%, and is also linked to deformed sperm and reduced sperm motility. Others say that there is no real evidence that time taken to conceive is materially affected by moderate coffee consumption. The overall message seems to be that anything above 300mg a day is bad news for baby-making, and lower intakes may or may not be a problem
The role of caffeine in raising blood pressure is uncertain. Caffeine does raise blood pressure for a period of time after taking it, but this appears to be short-lived, and to become less marked with more frequent use. The significance of this for the ordinary individual is uncertain, but people with raised blood pressure should probably reduce their caffeine intake
The role of caffeine in heart disease has been the subject of much conflicting opinion. Increased coffee consumption has been found to be associated with higher blood levels of homocysteine, which has recently been shown to be a risk factor for coronary heart disease. Similar studies showed an increase in LDL-cholesterol (the 'bad cholesterol', which increases heart-disease risk). These effects are not due to caffeine, but are due to coffee oils, which are only present in significant amounts in unfiltered coffee, such as that made in a cafetière or percolator. Instant coffee and paper-filtered coffee don't contain such significant amounts of coffee oils, and have not been shown to increase homocysteine levels and LDL-cholesterol in the same way. Whether these biochemical changes have been shown to lead to an increase in heart attacks in coffee drinkers is hotly disputed.
The overall consensus seems to be that it is probably not harmful, in most people, to drink between two and four cups of coffee daily, and there may be some health benefits at this level of intake.
The caffeine content of different drinks
Drink Caffeine content in mg Pepsi Cola 12oz 38 Dr Pepper 12oz 40 Coca Cola 12oz 46 Tea 7oz cup 60 Instant coffee 7oz cup 65-100 Percolated coffee 8oz cup 75-100 Espresso 1.5-2oz cup 85 'Drip' method coffee 8oz cup 95-150
