PREVENTIVE MEDECINE: RISK FACTORS IN CANCER RISING

Tobacco and alcohol

Consumption of these substances plays a substantial part in the rise of cancer levels as a community becomes westernized. Tobacco consumption is directly linked to cancer of the lung and bladder and probably to that of the pancreas. Cigarette consumption was low until 1973 in developing countries but as the public in the westernized world became aware of the dangers and tobacco consumption fell, the companies switched their sales to Third World countries. We can expect to see far more cancers in these countries as a result.

Alcohol interacts with tobacco as a causative agent in cancers of the gullet and larynx and independently of tobacco raises the level of cancer of the liver by producing cirrhosis. In contrast to the situation regarding tobacco consumption there is no direct and consistent relationship between alcohol consumption and economic development. Alcohol consumption is going up everywhere and there is evidence that cancer of the gullet is rising along with it.

Diet

Eating habits have always been a prime suspect as a cause of cancers but are difficult to convict conclusively. In general, westernized countries consume a diet high in energy, fat, protein and sugar and low in unrefined starch, dietary fibre, vitamins and minerals. Western diets make people fat and obesity has now been linked with an increased susceptibility to cancer. Several studies have found that tall, fat women are the most likely to develop breast cancer. Studies of Japanese women have linked the consumption of meat, eggs, butter and cheese to breast-cancer incidence. Breast cancer rates in rats can be greatly increased by feeding them diets high in fat. This raises their levels of prolactin (a hormone that acts on the breast).

Cancer of the body of the uterus (not the cervix) is more strongly linked with obesity than is breast cancer. Fat women seem to produce more oestrogens and these in turn may have a carcinogenic action on both breasts and uterus.

When we look at cancer of the colon the link seems to be with the increased consumption of meat and animal protein more than with fat. A study of Japanese migrants to Hawaii found that sufferers from cancer of the large bowel were more likely than control patients to have adopted a western style of diet and were about two and a half times more likely to have regularly eaten meat, particularly beef. Further support for this finding comes from the many studies done on the Seventh Day Adventists and other vegetarian groups in the US. They all have lower than expected colon-cancer rates. The Mormons, who are big beef consumers, also have low colon-cancer rates, so clearly beef is not the only answer. The worldwide level of cancer of the colon is related to the consumption of unrefined cereals and several experts have suggested that dietary fibre is protective in some way. This may be the result of its bulking action (which dilutes any carcinogens present in the food residue), or of its ability to increase the speed at which food residues pass through the colon (so reducing the amount of time a carcinogen is in contact with the bowel wall). Nobody knows for sure. Certainly studies have found that people with bulky stools have less colon cancer than those with hard, tarry stools. Fibre lack may well not be the only factor here though, and the answer will probably be found to be a combination of fat, meat and fibre-each of which causes has its champions in the scientific world of cancer research.

But we don’t learn about diet and cancer by looking only at the negatives. Stomach cancer has fallen dramatically this century and always falls when a country becomes westernized. No one knows why this should be but in Japan this decline in mortality is paralleled by an increasing consumption of meat, milk, eggs, oil and fruit. Studies of individual Japanese have found that two glasses of milk a day seem to be protective. The daily consumption of green or yellow vegetables appears to be protective too. Perhaps this decline is due to the increased consumption of vitamins A and C. Vitamin A has been shown to reduce the risk of experimentally-induced cancers in laboratory animals and there are several studies that suggest that it reduces the incidence of lung cancers in humans.

This brief survey of the major diseases of the western world shows clearly how they are linked to a western lifestyle, a fact that can be established both historically and by making comparisons with non-westernized peoples around the world today.

*66/72/5*

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