How much is enough? What is the range for healthy individuals? Is it normal? These are but a few of the many questions often asked of health practitioners, nutrition gurus, and physical activity advocates by individuals worried about “numbers”—for cholesterol, body fat, vitamins, minerals, and more. And while the need to be precise about numbers can become a matter of personal pride, the usage of terms that give those numbers their proper perspective can become somewhat jumbled. In science, particularly medical science, amount describes a quantity or sum—the total quantity of a given component present in things such as solutions or preparations: By the end of the experiment, the amount of reagent used exceeded 10 grams. In medical usage, concentration is also used to describe a quantity but one that is set within the context of another quantity. Thus, the relative content of any substance that is dissolved or dispersed within a solution or mixture is referred to as the concentration of that substance. For example, the concentration of cholesterol in the blood is usually measured in terms of one quantity, milligrams, of cholesterol set within the context of another quantity, usually deciliters, of blood. The use of the term level within a medical context, in comparison, is usually descriptive rather than quantitative, conveying a sense of the relation a particular range of concentrations has to a standard or normal concentration of a substance: Although low compared with that of other individuals of her age and weight, her blood sugar level had remained consistent for the past five checkups; therefore, no therapeutic action was considered necessary.
