ALCOHOL, TEA, COFFEE AND CANCER
Alcohol is produced when the sugars from fruits or cereals are fermented by yeasts to release CO2 from sugar (C6H12O6) giving ethanol (C2H5OH). When we drink alcohol, 20% is absorbed by the stomach and the small intestine from which it passes into the bloodstream and hence to all tissues and organs in the body (though it’s not taken up by adipose tissue because it doesn’t dissolve in fat). Eventually most gets broken down in the liver (90%) by the enzymes alcohol dehydrogenase (producing acetaldehyde) and aldehyde dehydrogenase. Alcohol consumption worldwide is estimated to cause about 4% of all cancers and there is evidence for specific association with most of the major cancers, including breast, mouth, oesophagus, pharynx and larynx, stomach, bowel, lung, liver (Fig. 1), ovary and prostate.
1. Human liver.
The mechanism by which alcohol promotes cancer is not clear although acetaldehyde may be mutagenic and alcohol itself acts as a local anaesthetic. Nevertheless, consumption is clearly linked to an increased risk of developing breast cancer. The Collaborative Group on Hormonal Factors in Breast Cancer (2002), referred to earlier in the context of tobacco, also showed that about 4% of the breast cancers in developed countries are attributable to alcohol. Compared with non-drinkers, women who consume one alcoholic drink a day have a very small increase in risk. Those who have two to five drinks daily have about one-and-a-half times the risk of women who drink no alcohol. The American Cancer Society recommends that women limit their consumption of alcohol to no more than one drink per day. One plausible explanation of its effects on the breast is that it elevates oestrogen production, which in turn increases cell growth.
Tea and coffee are the most common hot drinks in the world and it is well known that they contain the drug caffeine (a xanthine alkaloid) that can cross the blood-brain barrier and act on the central nervous system. So one might well ask, with all this drug abuse of our throats, is there any evidence that drinking tea or coffee gives us cancer? The most comprehensive analysis so far (of pooled data from nine case-control studies) shows, perhaps slightly surprisingly, that there is an inverse association between drinking caffeinated coffee and the risk of cancers of the mouth and pharynx. In other words, drinking coffee protects against these cancers and the more you drink, at least up to four cups per day, the greater the protection. For laryngeal cancer, however, drinking caffeinated coffee has no effect on the risk. The data on decaffeinated coffee is less solid but suggest that at least it does not increase risk. Tea drinking showed no association with head and neck cancer. The leaves of the Camellia tea plant are a particularly rich source of anti-oxidants in the form of polyphenols, and on a per serving basis coffee provides even more anti-oxidants. Substantial proportions appear to be absorbed by the body so it is possible that, through their anti-oxidant effects, they can inhibit mutagenic events.