Vitamins are organic compounds (compounds containing both carbon-carbon and carbon-hydrogen bonds) that are needed in small quantities for very specific functions, such as the main-tenance of regulatory and metabolic processes in the body. Consequently, vitamins (and minerals) are considered micronutrients, because they are required in much smaller amounts than macro-nutrients (carbohydrates, fat, protein, and water). In nearly all cases, human cells cannot synthesize vitamins, so it is essential to obtain them through diet. The few vitamins manufactured by the body (or by intestinal bac-teria) are not produced in amounts sufficient to meet our needs. If we don’t consume enough of a vitamin, or are unable to adequately absorb or utilize it, we may develop symptoms characteristic of an insufficiency of that vitamin.

In many cases, researchers discovered each of the individual vitamins by working backwards from symptoms or diseases that resulted from deficiencies—such as when people (or lowland gorillas) fell ill because they lacked enough of a particular vitamin. As we’ll discuss in Chapter 11, early pioneers in vitamin research recognized that there was a link between these unique and “vital” constituents in foods and the maintenance of health and body functions. The observations, research, and isolation of specific vitamins spanned decades and, even today, the door isn’t closed to the possible identification of additional vitamins.

Vitamins and macronutrients are essential nutrients found in foods, but they differ in significant ways. For instance, macronutrients in foods are typically complex structures that the body must break down into individual units before they can be utilized for energy or other functions; vitamins, in contrast, are already individual units. Macronutrients (including water) are also incorporated into structures of the cell—lipids, for example, are incorporated into cell membranes—but vitamins do not have this role in cellular structure. Finally, carbohydrates, lipids, and proteins provide energy; vitamins do not.