Primary care providers must be knowledgeable regarding the safety, efficacy, and drug interactions associated with common dietary supplements because of the following:

The U.S. Food and Drug Administration (FDA) is frequently criticized for not closely regulating dietary supplements and monitoring their safety. However, although the agency regulates prescription drugs and over-the-counter (OTC) products, the FDA has limited regulatory authority over dietary supplements. This is because the Dietary Supplement and Health Education Act (DSHEA) of 1994 and its resulting regulations limit the FDA’s authority. As a result of DSHEA, the FDA is able to act only when a dietary supplement has been documented to contain a prescription drug, as was the case with glyburide in a natural treatment for diabetes and diazepam in an osteoarthritis preparation. In addition, the FDA can act when safety issues related to a product have been clearly documented, although these cases are frequently challenged in the courts.

Dietary supplements generally are marketed under three types of health claims. The first category is the “nutrient content” claim, in which the product is identified as an excellent source of, typically, a mineral such as calcium, based on recommended daily values. The second type is the “significant scientific agreement” claim; these claims are used when some evidence of the product’s efficacy exists (e.g., fish oil supplements). The third and most common type of health claim is called a “structure/function” claim; these claims state that the product has some effect on health—for example, “helps to maintain a healthy heart.” However, dietary supplements are not permitted to carry claims stating that they are effective in preventing, treating, or curing diseases.

Appendix 1b provides a brief overview of common dietary supplements. Until recently, few evidence-based resources on dietary supplements were available. Clinical studies and systematic reviews on dietary supplements are now widely available through PubMed, EMBASE, and the Cochrane Database of Systematic Reviews. Although more information is available, references on specific products vary in their interpretation of the available evidence and may exhibit an unintentional bias, either pro or con, regarding the safety and efficacy of dietary supplements.

“Gold standard” evidence-based databases on dietary supplements (subscription required) include the following:

Evidence-based free websites on dietary supplements include the following:

Clinically significant interactions have been documented between dietary supplements and prescription or OTC drugs. The challenge for primary care providers is to identify real, clinically relevant interactions versus potential or theoretical interactions. Data on interactions with dietary supplements are usually based on isolated case reports or on studies enrolling healthy volunteers. As with drug-drug interactions, the likelihood of an interaction and its severity are influenced especially by concomitant medical conditions, such as heart failure and presence or absence of impaired kidney and liver function.

Appendix Ic lists interactions between selected natural products and prescription and nonprescription drugs. The following two broad interactions are particularly important in primary care practice:

The single most important counseling point related to dietary supplements is always to ask patients about their use of these products and to do so in an open, nonjudgmental manner. The approach should emphasize that many consumers have been interested in vitamins, minerals, herbs, teas, and so on, to maintain their health or to treat illness. If the clinician is unaware of the safety, efficacy, and interactions of a specific product, several websites are available to quickly scan for information. Also, access to drug information centers at colleges of pharmacy is almost always available, and some hospitals now offer programs in integrative medicine.

Patients should be asked about their goals in using the product, as well as how long they have taken it and in what dosage. Allergies to plants should be documented because cross-allergies are common. Clinicians should appreciate that an individual who uses dietary supplements may be interested in making lifestyle changes and potentially decreasing their use of prescription drugs. In addition, if an individual is also consulting an alternative medicine practitioner, clinicians should recognize that some alternative health systems discourage the use of established therapies such as vaccines.

Although problems with safety and efficacy have been identified, many dietary supplements are benign except for their cost. Some patients are at higher risk for adverse outcomes from the use of dietary supplements (e.g., those with chronic kidney and liver disease). Patients should be counseled specifically to avoid purchasing dietary supplements over the Internet.

Many clinical and observational studies of dietary supplements have been published. In the past, clinicians frequently stated that published studies of dietary supplements either did not exist or only a few were available. The reason for this finding was that until recently the National Library of Medicine did not abstract from the peer-reviewed alternative medicine literature. Fortunately, much more research is now readily available. As with all research, the more rigorous the study methodology, the less likely the dietary supplement is to demonstrate clinical benefit.

In evaluating published studies of dietary supplements, the following should be considered:

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