RECOMMENDED DIETARY INTAKES(RDI)

The body stores of vitamins vary from one individual to another according to the general state of nutrition and health. The stores of the fat-soluble vitamins are usually higher than those of the water-soluble vitamins. However, even the stores of the latter are sufficient to protect the well nourished individual for many days or even months. For example, it may take as long as 80-90 days before the symptoms of scurvy appear if one eats a diet without vitamin C.

It is estimated that body stores of vitamin B12 are adequate for more than two years and a diet lacking vitamin A will not lead to clinical signs of deficiency for several months.

Consequently, well nourished individuals are usually able to withstand periods of deprivation or periods of increased need such as occur with pregnancy and lactation. They are also at an advantage when stressed by disease or trauma. Undue concern about particular food preferences, for example about children who seem to want one kind of food and not another for a few days, is unnecessary. As long as a variety of foods are eaten over a period of time, the range of essential nutrients should be provided.

RDI's are the amounts of essential nutrients that are considered adequate to meet the nutritional requirements of healthy people. The RDI's are designed to easily prevent classical nutritional deficiency diseases, such as scurvy, beri-beri, pellagra, rickets and anaemia. Indeed, there is a wide margin of safety. However, they do not address the extra nutrient needs of persons with certain chronic ailments, who smoke, or who are on drug medication.

New research suggests a greater role for vitamins (and minerals) in the prevention or slowing down of many diseases such as heart disease, cancer, cataracts, osteoporosis and birth defects. The total effects of vitamins on the body are still not fully known or understood. Further, there is increasing scientific evidence to suggest that higher levels of certain vitamins (e.g. antioxidants vitamins C, E, and beta-carotene) may be necessary for optimal health, and may provide extra protection against cancer, heart disease and other diseases.

In time, the concept of RDI may well be broadened to include a second set of much higher vitamin levels that optimise their disease-preventing properties. From the medical practitioner's point of view, it is particularly important to remember that RDI's are for healthy people. In illness the requirements for many nutrients are altered. For example, with stress, trauma or surgery, the requirement for vitamin C may be more than 8 times the RDI for healthy adults; zinc requirements increase for wound healing.