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
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
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
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
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 reputationis 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
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.