Choosing a quality dietary supplement can be an exercise in abstraction. As a class of product nestled somewhere in between food and drug, they lack many of the obvious quality measurements inherent to these two other categories (such as the sensory properties one uses to select quality produce, or the strict quality control procedures inherent to the manufacture of a government-regulated pharmaceutical). Until recently, the only way to assess the quality of a supplement (short of spending a personal fortune on lab testing), was from the synthesis of subjective data (brand reputation, marketing claims, and personal experience).

The recent definition of the Good Manufacturing Practices (GMPs) for dietary supplement manufacturers by the Food and Drug Administration has significantly improved how supplement quality is viewed. The 1995 Dietary Supplement Health and Education Act (DSHEA), in addition to legally defining supplements and setting guidelines for their sale and marketing, also provided for a set of regulations governing their proper manufacture. It wasn’t until 2007, however, that these rules (the GMPs), were finally issued by the FDA. The GMPs are a set of requirements and expectations for the quality manufacturing, testing, and storage of dietary supplement products. They were phased in over a three year period; as of June 2010, all manufacturers are expected to be GMP-compliant. GMPs are a great benefit to consumers, and promise to dramatically improve confidence in their dietary supplement choices.

While generally viewed as a positive step, the implementation of the FDA GMPs is relatively new, and the regulations themselves still contain areas (such as testing requirements) that are not fully defined. It may also be some time before the FDA gets around to assessing the GMP compliance of every dietary supplement manufacturer, if they even choose to do so. Therefore it is useful to be familiar with other resources to determine the quality of a supplement product; this article outlines some of the most common.

What is Quality in a Dietary Supplement?
There are several ways to define quality for a supplement, but conventional assessments of supplement quality usually concentrate on two areas: adherence to label claims and freedom from adulteration.

It is fairly obvious that a quality supplement should contain the amounts of each ingredient (within an acceptable margin of error) stated in the Supplement Facts panel. Less commonly known, however, is that supplements are required to adhere to ANY claims made on the label. For example, if the label of a super-fruit supplement claims that it “contains pomegranate, an excellent source of potassium,” then the product is expected to contain potassium, even if it is not explicitly listed and quantified under in the Supplement Facts panel.

Although adulteration suggests some sort of malicious intentional contamination, in terms of GMP, it is officially used to describe any contamination of a dietary supplement product. This includes elevated levels of toxic metals (most commonly lead, mercury, cadmium, or arsenic), high levels of microbes (both benign organisms that can cause spoilage, and pathogenic ones that can cause illness), as well as toxins, either naturally-occurring or man-made (pesticides, herbicides, chemical wastes). A quality supplement product is one that can minimize or avoid the inclusion of any of these adulterants. Most often, adulteration occurs when a company misses key quality control procedures, although in some (rare) cases adulteration truly is an intentional act. The melamine contamination of wheat gluten and the “spiking” of some male enhancement supplements with generic sildenafil (Viagra) are two examples where manufacturers mingled legitimate supplements with other chemicals for a competitive advantage.

It is important to note that quality and efficacy are independent factors; what one considers to being a good or effective supplement product does not have to be one with the greatest quality (in the sildenafil example above, the supplement product was adulterated by a prescription drug, yet many consumers found it to work well). Similarly, there are many products in the marketplace that are made with quality ingredients under strict manufacturing guidelines, but contain amounts and combinations of ingredients that are less than the documented effective doses.

Usually, the company that designs, assembles, and packages a dietary supplement is distinct from the one(s) that manufacturers the individual ingredients that are contained in the supplement. Thus, ingredient quality and manufacturing quality can be treated as separate measures that must both be considered when choosing a quality supplement. A good manufacturer cannot make a quality supplement using poor quality ingredients, just as the best ingredient cannot add to the quality of a product if the manufacturer cannot reliably put the correct amount in the bottle. Many of the quality clues listed below, such as branded ingredients or manufacturing certification, only address one side of this quality equation.

Identifying Quality in a Supplement
There are several lines of evidence, both direct and indirect, that can be used to select a quality supplement. Some, such as third party product testing, directly demonstrate that the product adheres to label claims and represent the best affirmation of product quality. Unfortunately, only a fraction of the supplement market will ever get an independent test, so the savvy consumer must often look for other quality indicators when making a quality assessment.

Standardization can be an indirect measurement of ingredient quality. A standardized ingredient is one that contains a measurable amount of a particular compound. This is most often applied to extracts. An illustrative example would be for the herb milk thistle, a well-studied liver tonic and detoxicant. The milk thistle contains hundreds of different compounds; the most active for liver detoxification is the compound silymarin. There are any number of ways for preparing a milk thistle extract, however, only those that contain silymarin will be useful as liver supplements. Therefore, to guarantee the desired activity of milk thistle, manufacturers standardize their extract to silymarin; that is, they extract the seeds of the milk thistle in a way that preserves a consistent, measurable amount of silymarin. On a label, this might appear as “Milk thistle, standardized to 68 percent silymarin.”

When indicated on the label for a particular ingredient, standardization is one measure of ingredient quality because it can differentiate between ingredients that contain active fractions or are assumed to display an anticipated health benefit, and those that may not. Continuing the above example, compare a product containing milk thistle versus one containing milk thistle, 68 percent silymarin. The former could contain almost any mixture of milk thistle-derived chemicals, while the latter is enriched in liver-tonifying silymarin.

One of the most dramatic consequences of (the lack of) standardization is seen for red yeast rice, a potent cholesterol-lowering ingredient. Red yeast rice contains monacolins, which are chemically similar to the statin class of prescription drugs. Because of this similarity, federal regulations prevent red yeast rice products from bearing any standardization information. Not surprisingly, the unstandardized red yeast rice found in dietary supplements vary dramatically in their quality and efficacy. In a published analysis of commercial red yeast rice products, the amounts of monacolins differed between products by almost 100-fold.

Standardization, while a useful indicator, is not without its drawbacks; not all extracts are standardized (either due to limitations in laboratory analysis, or because researchers have not yet identified or agreed upon the correct standard), and understanding which standards to look for in each dietary extract requires a little research.

Branded ingredients are ingredients with their own branding, usually reflecting that the ingredient manufacturer has a specialized manufacturing technique, or has invested resources into validating the efficacy of their ingredient through animal or human clinical trials. Branded ingredients are often indicated as such on product labels. While not a direct quality measurement, branded ingredients are usually well tested (clinical trials require stricter analyses of potency and purity than those for inclusion in a supplement product), and many maintain their own websites where details of their quality and efficacy can be found.


strong>Adherence to pharmacopoeial monographs
Pharmacopoeiae are books of standards (called monographs) that are used to describe the manufacturing of a high quality pharmaceutical; many pharmacopoeia also contain monographs for dietary supplement ingredients. They are developed and maintained by independent organizations of scientists, and are available to manufacturers as guidelines for manufacturing quality. The most familiar (and most well-respected in the U.S.) is the United States Pharmacopoeia (USP); there are pharmacopoeial standards in other countries as well, as well as smaller, supplement-oriented collections (such as those by the Council for Responsible Nutrition (CRN)).

An ingredient that adheres to all of the standards set forth in a monograph (most of which involve measurements of potency, purity, and limits of contamination) is assumed to be a high quality ingredient. This is often indicated on the product label (for example, if a supplement contains the amino acid glutamine which meets all of the standards set out by the USP monograph, it can be labeled glutamine USP).

It is important to note that not all dietary supplements have monographs, so it is not always possible to assess standards by this method. Additionally, adherence to a monograph is voluntary and not independently verified. Most monographs in pharmacopoeia describe the quality standards for individual ingredients; there are standards for dietary supplement formulas, but these are rarely followed in commercial products (for example, the USP has a monograph for calcium plus vitamin D tablets that describes a product with a precise amount of calcium and vitamin D and no other nutrients; most supplement manufacturers would find this too limiting).

Separately from their pharmacopoeia monographs, the USP also maintains the USP Verified Dietary Supplement Ingredient Program, a voluntary program in which manufacturers can have individual ingredients verified for manufacturing consistency, meeting label claims for purity, potency, and quality, and acceptable limits of contamination. The USP website maintains a list of ingredients and manufacturers which have been verified under this program.

Manufacturing Certification. Although all dietary supplement manufacturers and distributors are required to adhere to the FDA GMPs, not all have been/will be audited by the FDA, so their compliance is not necessarily guaranteed. There are organizations, however, that perform independent audits of dietary supplement manufacturing facilities to certify that they are manufacturing using good practices. Both NSF International, a non-profit public health and safety organization, and the Natural Products Association (NPA), an industry trade group, offer certification of dietary supplement manufacturers for compliance to manufacturing standards that are consistent with, or exceed the requirements set out by the FDA. NSF also performs testing of individual products for adherence to label claims and adulterants. Both organizations maintain a list of their GMP certified companies on their respective websites; dietary supplement manufacturers certified by these groups may also include this information on their own websites.

Company reputation is the most subjective metric for assessing manufacturing quality, and one that should be weighted the most cautiously. Aside from the number of years a company has been in business (not always the best indicator of quality), one could look for more objective quality measurements, such how often the companies products pass third party testing, if it has had any product recalls, or whether it has received any FDA warning letters (the latter two are available from the FDA website).

As noted above, third party product testing of a supplement product, when available, is the strongest evident of individual product quality. Aside from the infrequent involuntary testing by the FDA, there are several organizations that provide independent testing of supplements. Some also audit the manufacturers directly, to evaluate manufacturing methods and quality control procedures.

The USP Dietary Supplement Verification Program is a voluntary product-testing program in which participating manufacturers volunteer their product for random, off-the-shelf testing by the USP. A product verified under this program bears the USP-Verified mark, which indicates that the product has met label claims, does not contain harmful levels of specified contaminants, will break down properly in the digestive system to release its ingredients, and has been manufactured according to the current FDA GMPs. Note that the USP does not have laboratory test for all dietary ingredients, so not all products can be verified under this program (herbal/botanical products, for example, are underrepresented amongst the list of USP verified supplements).

The TruLabel program of the Natural Products Association maintains a database of supplement labels from their participating member companies, and periodically selects products within the database for random testing to verify label claims. Some results can be found on their website.

Subscription services offer the most comprehensive collections of quality information for individual products; for a fee. ConsumerLab performs random, off-the-shelf testing (reviews) of individual supplement products, and also accepts voluntary product submissions from manufacturers for testing.

The monthly product reviews usually focus on a single product type, such as CoQ10 or enzyme products, for which testing results available to subscribers (non-subscribers can view a list of tested brands and a general summary of test results for free.) Products which pass testing can bear the CL Seal, and are added to the ConsumerLab Approved Products list. According to the group, they have reviews of over 2900 products from over 350 brands. Consumer Reports also maintains reviews of individual supplement products as well, and will indicate which ones have been USP verified.

Kevin M. Connolly, PhD