Researching Dietary Supplements

Despite their natural connotation, dietary supplements are biologically active substances. Evidence for their safety and efficacy should therefore be based on accepted principles of science.

What Is Good Science?

The Agency for Healthcare Research and Quality ranked scientific studies by the value of their results. Below they are ranked from most powerful to least powerful:
· prospective, randomized, double-blind, placebo-controlled clinical trial with crossover;
· prospective, randomized, double-blind clinical trial;
· single-blind clinical trial;
· open-label clinical trial;
· retrospective epidemiological study;
· other types of consumer or patient-based, interview-type studies (including meta-analyses).

Randomized, controlled trials are considered the gold standard of scientific research. Such trials include a control group, people who are observed but receive no treatment of any kind, and an intervention group, people who receive a certain treatment, such as a dietary supplement. Members of
the control and intervention groups are similar (matched) in age, sex, ethnicity, marital status, socioeconomic status, health status, and diet and are randomly assigned to the respective groups. The power of such a trial is that it controls for any variation between the two groups, so that the only relevant difference is that the intervention group receives the specific treatment. Thus, any difference in the outcomes between the control and intervention groups is likely attributable to the intervention.
To determine whether the results of a study are due to the intervention or to chance, scientists conduct statistical analyses. A P value (probability value) of 0.05 is generally used to indicate statistical significance. P values greater than 0.05 indicate that the likelihood the results were a product of chance is greater than 5 percent. Conversely, the smaller the P value, the more significant the results. Thus, a P value lower than 0.001 indicates that it is very unlikely the results were due to chance; that is, the intervention had a highly significant effect on the treatment group.
In case-control studies, cases who have a particular outcome (for example, a disease) are identified and their past exposure to various components (such as a dietary supplement) is compared with that of control subjects, who do not have the particular outcome. By matching case and control subjects for sex, age, and other variables, there is less chance that the results are due to anything but the difference in exposure.
Cross-sectional studies measure the prevalence of a health outcome (for example, a disease) or determinants of health (such as ethnicity) in a population at any one time. For example, a cross-sectional study could measure the relationship between osteoporosis and calcium intake. This type of study is vulnerable to confounding, however, as a result of selection bias, which distorts statistical analysis by including a sample
that is not representative of the population of interest. In addition, cross-sectional studies are not good for determining cause and effect.

Cohort studies are long-term studies that compare subjects who have a particular outcome (for example, a disease) and/or who receive a particular intervention (such as a dietary supplement) with those who do not have that outcome or exposure. Cohort studies tend to be less reliable than randomized, controlled trials because there is less control over the differences between the two groups. For more accurate results, cohort studies may have to last for several years, which allows for additional differences between the groups to enter into the study and confound the results.
The validity of a scientific study should determine whether it is published in a prestigious scientific journal, such as the Journal of the American Medical Association and the New England Journal of Medicine. Most scientific journals require that published material is reviewed by peers, other experts who can evaluate the strength of the evidence and identify shortcomings of studies. Published studies can be retrieved online at PubMed (see Appendix D).
Many dietary supplement manufacturers promote their products through testimonials and anecdotes from satisfied customers. While persuasive, testimonials cannot replace scientific evidence and are often fabricated, paid for, or provided by people who are emotionally bound to a product. Testimonials should never be substituted for rigorous scientific data.

Who Are the Experts?

Consumers get information about dietary supplements from many sources, including friends, family members, and
healthcare professionals. This information is often a mixture of scientific data, hearsay, and anecdote. Given the complexity of dietary supplements, however, only people with in-depth knowledge of science, medicine, and nutrition should be considered experts.
Registered dietitians, pharmacists, physicians, nurses, and physician assistants tend to be the most informed about the scientific evidence on dietary supplements. Registered dietitians are certified by the American Dietetic Association, and during the last several years, dietary supplements have become a major focus of their training and practice. In addition to answering specific questions about dietary supplements, a registered dietitian can determine individual nutrient needs based on age, sex, life stage (for instance, premenopausal versus postmenopausal women), and medical history. By analyzing the diet (including intake of fortified foods and dietary supplements), a registered dietitian can determine whether a person is consuming the recommended levels of nutrients or if any nutrients are lacking or being consumed in excess. Based on these results, a dietitian can recommend improvements to the diet and/or if dietary supplementation should be considered.
Pharmacists are trained to understand drug formulation and interactions. In addition to answering specific questions about dietary supplements, they can recognize potential interactions between dietary supplements and drugs. Pharmacists can also help identify those dietary supplements verified by the USP, ConsumerLab.com, or the NPA, as well as the recommended doses.
Physicians (MDs, DOs), nurses (RNs, NPs), and physician assistants are gradually becoming cognizant of the widespread use of dietary supplements. As a companion to the Physician's Desk Reference, an immense and detailed catalogue of drug and prescribing information that can be found in virtually any doctor's office or library, a new Physicians Desk Reference for Nonprescription Drugs, Dietary Supplements, and Herbs has been created. Physicians, nurses, and physician assistants can be useful resources regarding dietary supplements, including whether there is adequate evidence to support a benefit, no effect, or potential for harm.
People considering taking dietary supplements can benefit from consulting a knowledgeable expert. This is especially true for women who are breastfeeding or pregnant (or who may become pregnant); older individuals; people of smaller stature; people with chronic medical conditions such as cardiovascular disease, diabetes, or hypertension; and people with upcoming surgery. In addition, a pediatrician should be consulted when considering giving a dietary supplement to a child.

Dietary Supplement Information in the Media

Information about dietary supplements can also be found in books, magazines, newspapers, television shows, radio programs, and web sites, and these sources contain a range of reliable and unreliable information. Identifying accurate information should begin by determining the original source. If dietary supplement information does not come directly from an expert, it is important to establish whether an expert was consulted. (See Appendix D for a list of reliable resources on dietary supplements.)
Whether dietary supplement information is balanced, objective, and free of commercial influence can help determine if its motive is educational or promotional. Magazines and newspapers often contain full-page articles that seem to come from medical or scientific establishments;
upon closer examination, however, the word "advertisement" can often be found in small print at the top of the page, indicating that the information is indeed intended to sell something. Information contained in obvious advertisements can be misleading. Television commercials and lengthier infomer-cials are crafted so they appear to be backed by medical organizations. While these advertisements have the look and feel of a medical establishment, they are misleading and designed to sell a product to a vulnerable population.
Consider this common scenario: An attractive man or woman wearing a lab coat approaches the camera while speaking words of empathy to overweight viewers. "It's not your fault. You struggle with extra weight because of a malfunction in your body. Dietary Supplement X can reverse the effects of this malfunction and help you lose the extra pounds. Clinical trials have shown that people who take Dietary Supplement X lose weight faster and easier than those who do not take it." Inevitably, this monologue culminates in the opportunity to purchase Dietary Supplement X.
The format of information on dietary supplements can also provide cues as to its validity. Books, magazine and newspaper articles, and live newscasts deliver information in various levels of scope and depth. While a book might explore dietary supplements in great detail, a 60-second piece on the evening news might only offer tidbits that are sensational, very recent, or particularly interesting, without exploring the whole story. Shorter pieces, such as newspaper or magazine articles, may highlight the newest development regarding a dietary supplement but may not place this new information in context. Due to extended production and publication schedules, however, sources that do discuss dietary supplements in greater depth—such as books and encyclopedias—may not include the very latest information.