Vitamins and Minerals as Essential Dietary Components

The bulk of the food that we consume provides us with water, which accounts for 50% to 70% of our body weight, and the energy-yielding nutrients, such as carbohydrates (sugars and starches), lipids (fats), and proteins (Figure 1). In addition to these major nutrients, our bodies require a variety of other molecules and ions to maintain proper function. These nutrients, which are required in much smaller amounts, are known collectively as vitamins and minerals.

Figure 1 Carbohydrates, proteins, fats, and water account for most of our nutritional requirements. Vitamins and minerals are required in much smaller amounts, yet their contributions to the body's functioning are essential.

Fourteen vitamins have been shown to be essential for normal growth and health in humans. Vitamins are organic molecules (i.e., molecules containing the elements C, H, N, or O) that are needed in trace amounts to help catalyze many of the biochemical reactions in the body. The term "vitamin" derives from the words "vital amine," because the first vitamins to be discovered contained an amino group (-NR₂, where R is a hydrogen or some carbon-containing functional group) in their molecular structure. The fourteen vitamins that we know today do not have any particular structure in common, nor do they share a common function, but they can be divided into fat-soluble (nonpolar) and water-soluble (polar) molecules. In general, vitamins do not themselves provide chemical energy or act as biochemical building blocks for the body. Many vitamins (e.g., the B vitamins) assist enzymes (act as coenzymes) in activities ranging from vision to growth ability. (Enzymes are proteins or other molecules that catalyze reactions, i.e., make them go faster, without themselves being permanently transformed. You will learn about more catalysts and enzymes in the "Kinetics" experiment and the related tutorial, "Drug Strategies to Target HIV: Enzyme Kinetics and Enzyme Inhibitors".) Other vitamins, such as the antioxidants (e.g., vitamin C, vitamin E), help to maintain structures within cells.

Plants and bacteria have the enzymes necessary to synthesize their own vitamins; however, animals do not have the ability to synthesize vitamins and must consume them in the diet. (One exception is Vitamin D, which we can synthesize from cholesterol if we get enough sunlight.) Hence, we obtain our vitamins by eating plants or meat (and diary products) from animals that have eaten plants.

Minerals are typically defined by nutritionists as inorganic (not C, H, N, or O) elements, which are used in the body to help promote certain reactions, or form structures in the body. This definition differs slightly from (is a subset of) the usual chemical definition of a mineral, which is a naturally-occurring, nonmolecular solid. (A nonmolecular solid has a lattice structure rather than discrete molecular units.) We will use the nutritional definition in this tutorial. Minerals are typically consumed in the form of a salt containing the mineral element and another ion. For example, the calcium in Tums is in the form of calcium carbonate (CaCO₃). Minerals, like vitamins, perform a wide variety of functions in the body. Some, such as Mg²⁺ and Zn²⁺, enable enzymes to function, catalyzing biochemical reactions. Others, such as Na⁺, K⁺, Ca²⁺, and Cl^-, help to maintain electrical and water balance in the body, transmit nerve impulses, and stimulate muscle contraction. Still others, such as Ca and P, form the compound hydroxyapatite that is responsible for bone growth and structure.

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