13.2: Some Basic Vitamin Facts to Keep in Mind

In trying to separate fact from fiction, it helps to keep several truths in mind. First, we should keep before us the basic definition of a vitamin. Remember that it’s a substance which, in very small amounts, is essential in our diet; each and every vitamin is essential to our health and survival. It’s misleading to speak of an “essential” or “important” vitamin. Many advertisements use such language. If it’s a vitamin, it’s by definition essential and extremely important—a matter of health or sickness, life or death.

Second, we shouldn’t forget that a vitamin can’t be made by the body. So a vitamin must always come from an outside source. This is true even of the “outside” sources which are actually inside us—such as bacteria that make vitamins in our intestines. Remember, there are other substances which are necessary to human chemistry in very small amounts, but which the body can make. These can’t be defined as vitamins.

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An exception to the rule that vitamins can’t be made by the body is vitamin D, which can be made in the skin upon exposure to sunlight. If sun exposure is inadequate, vitamin D is required in the diet.

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Third, although in chapter 11 we saw vitamins at work as coenzymes, not all vitamins play such roles in taking food substances apart or putting them together as the chemicals of life. As we’ll see, vitamins have a variety of functions. One function of vitamin A, for example, is as a structural part of a molecule that plays a key role in vision.

Fourth, we need to have some idea of how much of a vitamin is needed. There’s a limit to the amounts our bodies can use. Beyond this limit, increased amounts of vitamins are pointless and may be harmful.

When vitamin intakes fall below a certain level, certain bodily chemical processes are inhibited. Body chemistry is either hampered, or is changed in injurious ways. The result is that symptoms of the deficiency begin to appear.

Fortunately, there are ways of detecting nutrient deficiencies before they occur. One is to measure a person’s stores of a vitamin or mineral—low stores indicating a vulnerability to deficiency (see Fig. 13-1). More commonly, a person’s dietary intake of nutrients is assessed and compared to recommended levels.

Dietary intake below the recommended amount is a measure of risk rather than an actual bodily deficiency. It’s a realistic measure in that it indicates an increased possibility of a deficiency, and calls for a closer look at the person involved.

Figure 13-1: Stages of Nutrient Deficiencies.

As will be discussed in Chapter 18, the recommended amounts are called Recommended Dietary Allowances (RDAs) and are decided upon by the expert committee of the Food and Nutrition Board. The RDAs include safety margins which go beyond the true requirements of most people. Thus, many people can fall short of such amounts with no physical trouble at all. The recommended amounts aren’t minimum requirements.