Rosalee Brown - DIETITIAN'S DESK

Vitamins and minerals are very important nutrients. They support many processes in the body related to growth and development. Many vitamins and minerals have major and minor functions but do not work in isolation. They often work in conjunction with other vitamins, micronutrients and/or minerals.

Take vitamin C, for example, which enhances the intestinal absorption of iron from plant sources. Excessive intake of iron in the presence of vitamin C can cause the oxidative breakdown of vitamin C, making null its enhancing effect on iron absorption. Supplementation with vitamin C can cause a change in the distribution of iron in people with medical problems related to iron overload. In these cases, iron held in cells of the spleen and liver can move to other areas in the liver causing damage.

High intakes of vitamin C (of one to five grams or more for two months or more) can affect the levels of copper in the blood and the protein that transport copper to tissues. Copper is vital in reducing free radical damage and the formation of melanin, the pigment important to hair and skin.

The body knows best

The important message here is that our bodies, in a healthy state, are capable of making their own regulatory determination of the amounts and frequency of the vitamins and minerals needed to carry out their functions. It can safely store what is needed. Trying intervene in the body's decision on daily vitamin and mineral requirements can disturb the delicate balance. This will work against us.

There are scientific guidelines for vitamin and mineral use. There is a dietary reference intake which is divided into:

1) The estimated average requirement (EAR) - amounts expected to satisfy the needs of 50 per cent of people in specific age groups.

2) Recommended dietary allowance (RDA) - level of daily intake of nutrients deemed sufficient to meet the requirements of nearly all healthy people based on gender and age.

3) Adequate intake (AI) - used where no RDA is established and the amount established is less firmly believed to be adequate for people in a particular age group.

4) Tolerable upper limits - the upper limit that can be consumed without known adverse effect.

The role of food

Foods supply the nutrients needed for growth, development and well-being. Eating wholesome foods is encouraged to supply nutrients. Many vitamins are affected by light, heat, water and other elements therefore, food sources of, for example, water-soluble vitamins such as fruits and vegetables, should be consumed daily in adequate amounts. They should be consumed as near to harvest as possible and where cooking is necessary, it should be a short time with limited water to reduce leaching. They should also be consumed as soon as possible after preparation.

Who needs supplements

These groups may need supplements - women of child-bearing may benefit from folate supplementation; older women may need additional calcium; persons who are chronic dieters; smokers; people who consume large amounts of alcohol and, of course, those with deficiencies.

Rosalee M. Brown is a registered dietitian/nutritionist who operates Integrated Nutrition and Health Services; email: yourhealth@gleanerjm.com.