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Vitamins: A Short Course For Pharmacists

Lauren S. Schlesselman, PharmD
Published Online: Sunday, February 1, 2004   [ Request Print ]

Although pharmacists are usually not experts in the area of nutrition, they are often the only health professional that patients approach with questions pertaining to nutrient supplementation. A common patient concern is how much of a vitamin is enough and whether a supplement is needed. To appropriately answer these questions, pharmacists should possess an understanding of dietary guidelines and recommendations.

Dietary Reference Intakes

The Food and Nutrition Board of the Institute of Medicine, National Academy of Sciences, publishes periodic reports called Recommended Dietary Allowances. They are now expanding these reports to include other nutrient-based reference values. These values are collectively referred to as the Dietary Reference Intakes (DRIs). The values include the Recommended Dietary Allowance (RDA), Adequate Intake (AI), Tolerable Upper Intake Level (UL), and Estimated Average Requirement (EAR). These values define the daily nutrient requirements necessary to maintain nutritional adequacy. These needs are based on nutritional components supplied by foods in the United States and Canada, not on supplementation. They take into account changing needs at various ages, gender, and life events (such as pregnancy).

The most commonly referenced DRI is the RDA, the average daily dietary intake level sufficient to meet the nutrient requirements for healthy individuals of a specific age and gender. Although the RDA is intended as a goal for daily intake, it is calculated as an average daily intake over time, rather than a specific requirement for each day. These recommendations should apply only to healthy individuals.

The RDA is derived from the EAR, which is calculated by evaluating all available scientific evidence pertaining to each nutrient. The EAR takes into account the amount of nutrient necessary to prevent symptoms of deficiency, to prevent symptoms of deficiency of other nutrients, and to prevent other chronic diseases, such as cardiovascular disease and cancer.

When data are insufficient to derive the EAR, the RDA is not calculated. In those cases, an AI is used instead. The AI, based on experimental data and approximations, is an educated judgment from the National Academies of Science. It is intended to meet or exceed the amount necessary to maintain a healthy nutritional state. AI values are provided for vitamin D and calcium (Tables 1 and 2).

In this era of megavitamins, the establishment of UL recommendations becomes more important. The UL represents the highest level of daily intake that is likely to pose no risk of adverse health effects. Unlike the RDA, the UL is not intended as a recommended level of intake, because no known health benefits exist when the RDA is exceeded.

Need for Supplementation

Patients take vitamin supplements for a variety of reasons. Some believe that their diets do not provide adequate amounts of vitamins. Others believe that supplementation, especially in megadoses, will prevent chronic illnesses. A look at both of these reasons follows.

Although the typical American diet consists of fast food and other meals on the go, recent surveys show that Americans meet or exceed daily recommendations for some nutrients. In particular, nutritional intake is sufficient for vitamin C, thiamine, riboflavin, niacin, and phosphorus. For other vitamins, the intake was in the range of 70% to 80% of what is recommended. Because these surveys consist of self-reported food intake, the true food consumption is often underreported. Therefore, the intake of other vitamins also is underreported and may actually meet daily requirements.

The American Heart Association (AHA) recommends adequate nutrition, rather than supplementation, as a means to meet daily needs. The AHA suggests a nutritious diet consisting of a variety of foods in moderation. The American Dietetic Association maintains a similar position and promotes additional vitamins and minerals only for patients whose nutritional needs cannot be met through a varied diet.

Vitamins are necessary for energy production, growth, and maintenance. They do not prevent the common cold, enhance athletic performance, or increase strength. This fact is particularly true of megadoses of vitamins. No scientific data support the ingestion of vitamins in excess of the RDA by healthy individuals.

Individuals with chronic conditions or undergoing life events will have unique nutritional needs. Patients undergoing dialysis often require supplementation of B vitamins, and pregnant women need folate and iron. Individuals who eat vegetarian diets typically have zinc requirements twice those of nonvegetarians.

In patients without these unique circumstances, excessive doses of vitamins may cause adverse effects. Excessive vitamin C, for example, is associated with diarrhea and kidney stones, and excessive vitamin B6 can produce irreversible numbness and tingling in the arms and legs.

Many patients are interested in antioxidant vitamins. This interest is based on observational studies in healthy adults consuming large doses. These studies do not prove a cause-and-effect relationship. Scientific trials are under way to determine the benefits of antioxidant therapy. So far evidence does not suggest that antioxidants reduce the need to treat hypertension or hypercholesterolemia, or to quit smoking.

Conclusion

Although nutritionists remain the experts on vitamins and minerals, pharmacists can provide a valuable service to their patients if they are knowledgeable about national guidelines. Understanding the DRI values will aid pharmacists in explaining these requirements to their patients. The DRI values are useful tools to guide recommendations, but pharmacists should remember to refer patients with unique health situations to a qualified nutritionist or physician for further assessment.

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