MICRONUTRIENTS, DIETARY QUESTIONNAIRES AND CANCER

There is increasing evidence that many chemicals, although present in the diet al only low levels, play an important role in protection agai nst cancer. Micronutrients are defined as nutrients present in the bod y in amounts less than 0.005% of body weight. Some micronutrients sugg ested to play a protective role in cancer are beta-carotene, vitamin E and vitamin C. In addition to those chemicals with an established rol e in nutrition, there is also a less well-defined group of chemicals, often referred to as phytochemicals, which may prove even more importa nt. Examples here are a group of sulphur-containing chemicals present in brassicaceous vegetables, such as broccoli and cabbage, that appear to be very effective anticarcinogens. Epidemiology will be essential in accurately defining the role of phytochemicals and micronutrients i n cancer. However, the large prospective studies that would be most de sirable increasingly utilize food frequency questionnaires containing a limited number of questions. Such an approach has been well validate d for macronutrients. However, there is often less accurate informatio n available on micronutrients and phytochemicals, and the food combina tions necessary (and acceptable) for macronutrients may be inappropria te for these other factors. It would be most desirable that fruits and vegetables are individually itemized or grouped according to plant fa milies rather than macronutrient status. This map be the most appropri ate way of identifying potentially novel protective factors in the die ts of countries such as Morocco or New Zealand.