Diet nutrition and cancer (Conclusion)

Population life cycle: time-related changes in infective cancers

The pattern of cancer varies widely from one country to another, broadly matching the level of economic developing countries. Thus for example, in developing countries in Asia and Africa, the most common cancers are those of the mouth and pharynx, larynx, esophagus, stomach, and liver. This contrasts with the pattern seen in economically developed countries in Europe and North America, where cancers of the colon, breast, prostate, and body of the uterus are most common. This cross-sectional difference masks the changes that have taken place in time.

Cancer of the stomach was much more common in Europe 50 years ago, but there has been a dramatic, progressive decrease by at least 50 percent since then. This suggests strongly that within societies there are patterns of cancer that change in risk for successive cohorts of the population. It is highly suggestive that this cohort effect is a consequence of changes in the environment that expose different age groups to a potentially toxic environment at a particularly sensitive stage of the development of susceptible individuals within the society.

This change of patterns can be most graphically illustrated by the changing patterns of cancer experienced by migrant population, who retain common genetic characteristics while experiencing substantial change in environmental exposure. Thus, the pattern of cancer changes as the children and grandchildren of Japanese migrants to Hawaii become increasingly exposed to the new environment. Cancer of the stomach decreased from 40 to 20 to 12 per 100,000 from the parents’ generation in Japan to the first and then the second generation in Hawaii.

By contrast, cancers of the stomach and rectum increased from 4 to 18 by the first generation and cancer of the breast from 11 to 33 per 100,000 over the 3 generations. These dramatic patterns of change within relatively short times indicate very powerful effects of different environments for different risk factors at critical periods during the life cycle, which tend to be cumulative from one generation to the next. Cancers that are more prevalent in developing countries have broad characteristics in common.

Thus, if one uses cancers of the stomach, cervix, or liver as examples, each appears against the background that is broadly characterized as having an inflammatory base associated with a diet of poor quality and, for some exposures, limitation of specific nutrients. Cancer of the stomach is caused by behavioral factors, such as the consumption of salted fish prepared in a particular way that is likely to produce local irritation and inflammation, thereby predisposing to infection with the bacterium Helicobacter pylori, against the background of limited anti-inflammatory and antioxidant protection.

Changes in behavior, such as a reduction in the consumption of salted fish or wider access to and use of refrigeration, which helps to increase the consumption of fresh fruit and vegetables, together reduce inflammation and enhance antioxidant capability. Cancer of the cervix is caused by the human papilloma virus, but the risk of infection is determined by behavioral consideration and sexual practice; however, there is also a direct interaction with folate status, which is enhanced with the consumption of fresh fruit and vegetables.

Thus, a change in sexual behavior and improved diet together help to minimize the risk of developing cancer or the likelihood of the cancer progressing. Cancer of the liver is caused by factors associated with an unclean environment and unhygienic behavior: infection with hepatitis virus or consumption of food contaminated by aflatoxin. Both lead to an inflamed and scarred liver, and this process may be made worse by excessive consumption of alcohol or unregulated absorption of iron. It is not clear for any of these cancers whether poor nutritional status predisposes infection, thereby establishing the cancer process, or whether infection predisposes to poor nutritional status, thereby enabling progression of the cancer process, or whether other, more complex, patterns of interaction are involved.

However, all represent a feature of a potentially hospital environment in which an inflammatory process – whether the consequence of infection, a toxin, or physically damaging exposure in a cellular environment that is nutritionally poor – increases the likelihood that rapidly replicating cells are likely to experience greater DNA damage, which is less likely to be identified and corrected. In intergenerational terms for the population, each cancer rapidly becomes less common when the underlying environmental factors have been improved.