By: Prof. Dr. Mikael Rørth, Rigshospitalet (University Hospital), Copenhagen

Nowadays, in modern Western society, cardiovascular disease and cancer are by far the most frequent causes of death.

As regards both groups of diseases, we know a great deal about causal connections, which now makes it possible to prevent many cases of illness, and thus deaths, and at a relatively early age. The major single factor for both diseases is tobacco smoking. And without doubt the most effective way to reduce the risk of contracting these diseases is to stop smoking tobacco. In Denmark, for example it is reckoned that more than 30% of all cancer cases are related to smoking tobacco.

The influence of diet
Many people claim that just as many or even more cases are determined by various factors related to our diet. However, the causal connections relating to diet are not as explicit.

There are many factors in our diet that may influence the development of cancer, either as initiators (that start the process that leads to cancer) or promotors (that accelerate the initiated process). Other diet factors may have antioxidant properties or in other ways reduce the risk of cancer initiation.

From epidemiological studies, i.e., comparing sections of populations, or from studies on people who have moved from one culture to another, it has been possible to point out certain connections between diet and the occurrence of cancer. This is especially the case with Japanese people who have moved to the USA.

Excessive consumption of calories in general increases the risk of getting breast cancer. Excessive consumption of fat increases the risk of getting cancer in the breast, large intestine, rectum, and prostate. Excessive consumption of meat increases the risk of cancer in the rectum and a high consumption of nitrates/nitrites increases the risk of cancer of the stomach.

A low consumption of fruit, vegetables and vitamin C also increases the risk of cancer of the stomach. A low consumption of cabbage and dietary fibre increases the risk of cancer in the large intestines, while low consumption of betacarotene, vitamin E and selenium is connected with the risk of contracting a number of cancers, including those related to tobacco smoking, such as lung cancer.

Difficulties of prevention
These connections are however only indirectly verifiable and it has proven quite difficult to use this knowledge as a viable means of intervention in reducing the risks to people who might be exposed to them. For example, in large clinical studies conducted in both Finland and the United States, heavy smokers have been given betacarotene as a supplement to their diet in order to reduce the risk of developing lung cancer. Surprisingly enough, however, in both studies the findings showed that those who received betacarotene had an increased risk of developing cancer of the lung.

These results obviously do not exclude evidence that the consumption of carotenes and other antioxidants from vegetables can help against cancer – the many indirect research projects are significant enough – they simply demonstrate that supplements of single components of this type cannot be recommended as such. It also shows that it is necessary to conduct large-scale intervention studies before it is possible to make recommendations to populations as regards this kind of dietary supplement.

Dangerous fast-food
Our diet patterns in the Western world involve a high consumption of energy, fat, and animal protein and are known to contribute to the relatively frequent appearance of cancers such as cancer of the breast, large intestine and maybe of the prostate and uterus. Modern lifestyles with too little exercise and too much fat food, such as "fast-food", lead to obesity and an increased risk of developing cancer and cardiovascular diseases. For many of these diseases, current treatments are not effective or have many side effects, which is why there is a good reason to concentrate intensively on prevention. And it has to be done quickly.

If we are asked to advise on a preventive effort against cancer disease on the basis of current knowledge of the influence of diet, this must include: A reasonable, low amount of calorie consumption, so that obesity is avoided; less fat, especially from animals, more carbohydrates, and less meat – all factors that also help lessen the risk of cardiovascular disease. Regular physical activity (exercise) also has a documented positive influence on both cancer and cardiovascular diseases. From a large Norwegian study it has been concluded that a moderate amount of exercise reduced the risk of breast cancer in women.

Healthy living
Even though we do not always understand the details of how the mechanisms work, it is clear that with intensive effort in these areas it is possible to prevent many serious illnesses. In this connection it is ‘lucky’ that the prevention of both cardiovascular disease and of cancer can be managed in this way. However, one single important exception should be mentioned. While the daily consumption of a certain amount of alcohol (approximately 2 units daily for women and 3 for men) may reduce the risk of cardiovascular disease, alcohol is a risk factor as regards developing cancer of the mouth, throat, larynx and liver.

A healthy lifestyle means exercise, avoiding obesity, eating fruit and vegetables, modest consumption of fat or meat from animals, and, most important, quitting smoking.