Most doctors and dietitians agree that an adequate diet selected from a range of foods in the Five Food Groups and taken in the recommended portion sizes, will ensure a satisfactory intake of all nutrients, including vitamins. However, it is also recognised that vitamins which are constantly needed in the metabolism can be compared to an integral part of a work force on a factory assembly line. Each worker has a specific and vitally important role to play and his absence can jeopardise the smooth running of the whole system.
In the case of an unsatisfactory vitamin intake, one should first and foremost try to rectify the situation by improving one's diet, as food sources of vitamin also include other essential nutrients - some of which may still be unknown. Incidentally, the reason for choosing a food source rather than a vitamin in pill form is not that one's system absorbs it better - the body is in fact unable to distinguish between natural and synthetic compounds in this way. Each vitamin - whether manmade or naturally available - is a very specific compound with a unique molecular structure which is handled by the body in a particular way.
Supplements should however be considered only if, for some reason, your vitamin needs exceed your dietary intake. For example, people on strict long-term weight-reducing diets, heavy smokers and drinkers, pregnant women taking a less-than-optimal diet to cover the needs of two, or people living in isolated areas (or away on expeditions) who are unable to obtain the necessary variety of foods, may all benefit from vitamin supplements. (Incidentally, a pregnant woman should always take a supplement under a doctor's supervision only.)
A recent study (by Macfarlane et al) on 774 Indian women in Durban showed that 25% had iron deficiency anaemia and an additional 17% showed sub-clinical signs of this deficiency disease. The authors concluded that South African Indian women should receive iron supplementaton during pregnancy, as their cultural dietary habits promote an inadequate intake of this important trace element.
It has also been found that heavy smokers need more vitamin C than do non-smokers, as smoking seems to reduce the availability of vitamin C in food to the body.
The dangers of the overdose
Megadoses of vitamins are a different story. Some people assume that if a small amount of a vitamin supplement is useful under certain circumstances, more would be even better, but this is not so - in fact, abnormally large quantities of the fat-soluble vitamins (A,D,E and K) can be toxic as they accumulate in the body and excesses are not immediately lost in the urine, as is usually the case with water-soluble vitamins. However, care should be taken even with the latter: cases of `rebound scurvy' have occurred in babies whose mothers have taken excessive amounts of vitamin C during pregnancy - with the result that the baby's body reacts as if deprived when it has to depend on its own food intake after birth.
A recent study (by Read et al) in which people in seven states in the USA were questioned about their health beliefs showed that regular supplement users (who were predominantly married Caucasian women between the ages of 20 and 79) believed that supplements decreased their susceptibility to health problems ranging from colds to heart attacks and cancer, and/or reduced the severity of those problems. They also found that the higher the user's level of education, the larger the number of supplements taken, but the bottom line of the study was that more non-users rated their health as 'excellent' than regular users. The authors concluded that it remains a paradox that the well-educated, settled members of the community who are in a position to obtain all their nutrient requirements from a balanced diet, continue to be the most regular users of vitamin and mineral supplements.
