Nutritional intervention studies in cancer prevention.

Nutritional intervention trials are important tools in the search for efficient cancer prevention strategies. They can be divided into two types of trials; chemoprevention in which intervention is a defined chemical agent or a micronutrient, and diet trials in which intervention is a change in dietary habits. The most commonly used chemopreventive agents are retinoids, beta-carotene, and vitamins. The chemopreventive trials are directed to general cancer prevention or focus on target organs. The diet intervention studies include subjects at increased risk for cancer, cancer patients and community-based intervention programs. Although several completed chemopreventive studies indicate that certain micronutrients can prevent neoplastic growth, the follow-up period is still too short for most nutritional intervention studies to determine whether their preventive strategies are effective.