How do I know if a supplement is high quality?

Quality is a chain of custody with five links: follow the tub backwards from the sale to the raw material, and the document that proves each of the first three links

How do I know if a supplement is high quality is a question most people try to answer from the front of the tub, and the front of the tub is the one place the answer is not, because the front is written by the brand to be read by the buyer. The answer is behind the tub, in the chain of custody, the sequence of hands and documents through which an ingredient became a capsule in a kitchen, and the useful thing is that the chain has five links, each with a document, and a high quality supplement is simply one whose chain is documented at every link while a low quality one is one whose chain has a gap. A buyer follows the chain backwards, from the sale to the raw material, because the links nearest the buyer are the easiest to check and the gaps are usually in the middle.

The first link backwards is the sale, and its document is on the tub: the name and address of the food business operator responsible for the product, required by law on every supplement sold in the UK, which names the company that answers for the tub and gives the buyer someone to write to. A tub without it has a chain that ends at a warehouse, and nobody in the UK answers for it; a tub with it has a chain that can be followed, and the operator can be checked in the company register for its history. The second link backwards is storage: the shelf life printed on the tub was set, in a well-run brand, by stability data, the testing of the product over time under stated conditions that shows how long the labelled content lasts, and the tub was kept within those conditions between the factory and the shelf; the document is the brand's stability study, which a buyer rarely sees, and the proxy is an expiry date that is set from the fill date and a product whose storage conditions are stated and sensible, with the oils and the live cultures being the products where this link breaks most often on a long import.

The third link backwards is release, and it is the centre of the chain and the gap a buyer finds most often. Before a batch of finished product is allowed out for sale, a well-run brand tests it against a release specification, the assay of the active against the label within the tolerances, the heavy metals against limits, the microbial counts against limits, sometimes the disintegration of the capsule, and records the result on a certificate of analysis for that batch, from an accredited laboratory for the tests that need one; the batch is released if it passes and rejected if it does not. The document is that certificate, identified by the lot number printed on the tub, and it is the one document a buyer can ask for and a brand with a documented chain can send. The commonest gap in the whole market sits here: a brand that buys finished product from a contract manufacturer, puts its label on it and never sees a batch result has a chain that is documented at manufacture and at sale and empty in the middle, and the brand's own quality is whatever the manufacturer's was, unverified.

Three links followed backwards from the tub to the release document, and the two links behind them, manufacture and raw material, the one question that tests the whole chain, and the worked example traced, which is the next section.

The fourth and fifth links, manufacture and raw material, and their documents; the one question that tests the whole chain and how the reply is read; what the chain does not tell a buyer; the worked example traced link by link; and the verdict

The fourth link backwards is manufacture: the facility where the product was made, and its document is a certification to a named standard, good manufacturing practice under the food or medicines framework and, for many UK facilities, the retail consortium's standard, both audited by a third party on a schedule, with the certificate carrying the facility's name and the certifier's. A brand states which standard its facility holds and a buyer verifies the certificate with the certifier; a brand that says made to high standards without naming one has not documented the link. The fifth and last link backwards is the raw material: the ingredient arrived at the facility with a certificate from its supplier stating its identity, assay and contaminants, and a well-run manufacturer verified that certificate by testing the incoming material rather than taking it on trust, because the raw material is where heavy metals in a mineral and adulterants in a botanical enter the chain. The document is the supplier's certificate and the manufacturer's incoming test, and a buyer rarely sees either, but a brand that can describe where its ingredient comes from and how it is verified on arrival has a chain that reaches all the way back, and a brand that does not know has a chain that starts at its own label.

One question tests the whole chain, and it is the release link's question: an email to the brand with the lot number from the tub, asking for the certificate of analysis for that batch. The reply is read for more than the certificate. A brand that sends it within days, naming the laboratory and the tests, holds the release document and almost always holds the links on either side of it, because a brand that releases against a specification knows its facility's standard and its ingredient's source. A brand that sends a general statement about testing, a certificate for a different lot, or a redacted document has a gap at the release link and probably at the raw material link too. A brand that does not reply has told the buyer where the chain ends. The question costs nothing and reads the chain from its centre outward.

What the chain does not tell a buyer is worth a sentence so that it is not asked to: it covers whether the tub contains what the label says, made and kept properly, and answered for by a named company. It does not cover whether the product does anything, which is the evidence question answered by the trials and the claims register, nor whether the dose suits the buyer, nor whether the price is fair; a product can have a perfect chain and no evidence, and the chain is the quality half of a purchase, with the evidence being the other half.

The worked example is traced link by link in the open: {FL} carries a UK operator's address on the tub, a UK company on the company register, for the sale link; an expiry set from the fill date for a dry capsule with no cold chain to break, for the storage link; each batch released against specification with lead, mercury, arsenic and cadmium tested at an accredited UK laboratory and the certificate available by lot number on request, for the release link; a UK facility certified to GMP and BRC, for the manufacture link; and a magnesium bisglycinate raw material supplied with a certificate and verified on arrival, for the raw material link. It is 1500mg magnesium bisglycinate stated as 300mg elemental at 80% NRV, two capsules with the evening meal, 180 capsules for £19.99 at 22p a day. The full label breakdown is here.

The verdict: a supplement is high quality when its chain of custody is documented at all five links, and a buyer follows the chain backwards from the tub: a named operator with an address for the sale, a shelf life set by stability data for storage, a certificate of analysis by lot for release, a named and audited standard for manufacture, and a verified supplier certificate for the raw material. One email asking for the lot's certificate tests the chain from the centre, and the commonest gap is a brand that has never seen its own batch result.

What to check on the label

Questions people also ask

What makes a supplement high quality?

A documented chain of custody at all five links: a named operator with an address answering for the sale, a shelf life set by stability data and kept within its conditions, a finished batch released against a specification with a certificate of analysis by lot number, a facility certified to a named and audited standard, and a raw material that arrived with a supplier's certificate and was verified on arrival; the front of the tub says none of this, and a buyer follows the chain backwards from the sale to the raw material, with one email for the lot's certificate testing it from the centre.

How can I check if a supplement is good quality before buying?

Three links are checkable before the purchase: the operator's name and address on the listing or label, searched in the company register for a trading history; the expiry and the stated storage conditions, with oils and live cultures on long imports being where the storage link breaks; and the brand's statement of its manufacturing standard, GMP and for many UK facilities BRC, verifiable with the certifier; the release link, the certificate of analysis by lot number, is tested after purchase with one email, and a brand that cannot send it has the commonest gap in the market.

What is a certificate of analysis and why does it matter?

The release link's document: before a batch is allowed out for sale, a well-run brand tests it against a release specification, the assay of the active against the label within tolerances, heavy metals and microbial counts against limits, sometimes disintegration, at an accredited laboratory for the tests that need one, and records the result on a certificate identified by the lot number printed on the tub; it is the one document a buyer can ask for and a brand with a documented chain can send, and its absence means the brand has never seen its own batch result.

Does a high quality supplement mean it works?

No; the chain of custody covers whether the tub contains what the label says, made and kept properly and answered for by a named company, and it does not cover whether the product does anything, whether the dose suits the buyer or whether the price is fair, which are answered by the trials, the claims register and the arithmetic of price against effect; a product can have a perfect chain and no evidence, so the chain is the quality half of a purchase and the evidence is the other half, and a buyer checks both.

Is this site's magnesium high quality by this test?

Each link is documented in the open: a UK operator's address on the tub and a UK company on the company register for the sale, an expiry set from the fill date for a dry capsule with no cold chain to break, each batch released against specification with lead, mercury, arsenic and cadmium tested at an accredited UK laboratory and the certificate available by lot number on request, a UK facility certified to GMP and BRC, and a magnesium bisglycinate raw material supplied with a certificate and verified on arrival; 300mg elemental at 80% NRV in two capsules with the evening meal at 22p a day.

Sources

1. The supplement manufacturing standards: Good Manufacturing Practice, the BRCGS Global Standard for Food Safety and ISO 22000 are the facility-level certifications a contract manufacturer holds and a brand may cite. https://www.brcgs.com/our-standards/food-safety/
2. The batch release and certificate of analysis framework: a product has a written specification for identity, assay, contaminants and physical properties, each batch is tested against it before release, and the certificate of analysis for a batch reports the results against the specification, so that batch-to-batch consistency is read by comparing certificates across lot numbers. PubMed record
3. The stability and shelf-life testing framework: a declared best-before date is supported by real-time or accelerated stability studies showing the labelled content is still present at the end of shelf life, the test that connects a label number to a tub opened a year later. PubMed record
4. ISO/IEC 17025, the standard for testing and calibration laboratories: accreditation to it by a national body attests to a laboratory's technical competence and the validity of its results for the methods in scope, and is what makes a certificate of analysis a document someone has audited. https://www.ukas.com/accreditation/standards/laboratory-accreditation/

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