1. CAUSES OF CANCER
Sources of damaging agent:
Which are more important in terms of cancer aetiology?
Doll and Peto analysed many epidemiological studies to arrive at estimates of the contribution to cancer from various sources:
(From "The causes of cancer: quantitative estimates of avoidable risks of cancer in the United States today." 1981)
Causes of cancer
- Smoking accounts for about one in 3 cases of cancer
- Diet is responsible for about the same proportion
confirmed in a paper from Walter Willett in 1995
- Environmental and occupational exposure account for only a few percent.
The public tend to perceive environmental chemicals as a major threat, while being reluctant to act on the causes they can control - smoking and diet.
Nutrition is complicated; the lack of ‘good’ things in the diet is as important as the presence of ‘bad’ things.
Natural mutagens in food?
Ames has listed a large number of naturally occurring substances in food (i.e. not additives or contaminants) that have been shown to be
mutagenic (causing mutations in cells, usually bacteria) and/or carcinogenic (causing cancer in experimental animals). Yet they (apparently) don’t cause cancer.
A few examples:
- Hydrazines in edible mushrooms
- Furocoumarins (e.g. psoralen) in celery, parsnips, parsley etc. - light-activated carcinogens
- Glycoalkaloids in potatoes
- Quercetin (flavonoid) in many vegetables, tea etc.
- Theobromine - 2% of dry weight of cocoa
Inappropriate doses? Very efficient repair? Overwhelmingly protective effects of other plant compounds? Endogenous damage most important?