What company has the purest supplements?

Pure is three words at three corners: contaminants, excipients and potency, what each is measured in, why no company sits at all three, and why purity marketing names none of them

What company has the purest supplements is a question that cannot be answered until pure is given a meaning, because it has three, and they pull against each other. The first corner of the triangle is purity from contaminants: the heavy metals, lead, mercury, arsenic and cadmium, that arrive in a mineral or a plant extract from the soil and the process, measured in parts per million by mass spectrometry, and the microbial load, total counts, yeasts and moulds and the named pathogens, measured in colony-forming units by culture, both reported on a certificate of analysis for a specific batch against specification limits. The second corner is purity as in only: the fewest ingredients in the capsule beyond the active, the excipients, flow agents, anti-caking agents, colours, coatings and fillers that make a capsule fillable on a machine and a tablet pressable, read from the ingredient list in descending order of weight. The third corner is purity as in potency: that the assayed amount of the active in the finished product matches the label within the tolerances the European guidance allows, which is a release test on each batch rather than a label statement, and which separates a product that contains what it says from one that contains the right ingredients in the wrong amount.

No company sits at all three corners at once, and the reasons are mechanical rather than moral. A capsule with no excipients at all, the pure active and a shell, is harder to fill accurately on a machine, because the powder does not flow evenly without an agent, so the second corner costs the third a little unless the fill is slow and expensive. A product with the lowest possible metals may achieve it by diluting a botanical extract with a filler, buying the first corner with the second. A high-potency product with a large active dose per capsule leaves no room for excipients and reaches the second corner by default, while a low-dose vitamin needs a filler to make a capsule large enough to handle, and no amount of purity marketing changes the physics of a capsule. A buyer who understands the triangle stops looking for the purest company and starts asking which corner matters for the product in their hand: metals for a mineral or a mushroom extract grown in soil, excipients for a person with an intolerance or an objection to a specific additive, potency for anything where the dose is the point.

Purity marketing names none of the three corners, which is how it can be recognised. A brand that says pure, clean, nothing artificial or no nasties has made a claim that lives at no corner and is proven by no document, and the claims register that governs health claims does not govern the word pure, so it is used freely. A brand at a real corner says which one and shows the document: the metals certificate with the figures and the limits, the ingredient list of three items, the assay result against the label. The difference between the two is the difference between a word and a measurement, and the next section is about the measurements, how to get them and how to read them.

Three corners, a triangle no company fills and a word that names no corner, and the documents that prove each corner, the request that gets them and the worked example, which is the next section.

The document for each corner and how to request it, what a refusal means, the brand in the question left unnamed, the worked example placed at its corners, and the verdict

The first corner is proven by a certificate of analysis for the batch in the tub, issued by a laboratory, listing each metal with its result and its limit, the microbial counts with theirs, the method used and the laboratory's accreditation, and a buyer requests it by emailing the brand with the lot number printed on the tub and asking for the certificate for that lot. A brand at the first corner sends it within days, often with the accreditation certificate of the laboratory alongside, because the document exists for every batch and sending it costs nothing. A brand that replies with a general statement about testing, a certificate for a different lot, a redacted document with the figures blacked out, or nothing, has told the buyer which corner it is not at, and the refusal is the answer. The second corner is proven by the ingredient list on the label, read in descending order of weight, where the active comes first and everything after it is excipient, and a buyer counts the items and looks up any they do not recognise; it is the one corner that needs no request. The third corner is proven by a release specification and the batch's result against it, the assay of the active compared with the label within the legal tolerance, which a brand at the third corner can send with the metals certificate and which a brand that buys finished product from a contract manufacturer may never have seen.

No brand is named in the body of this page, by rule, and the rule has a reason that fits the question: a brand that has built its name on purity is judged here by the same three documents as every other brand, not by its reputation or its claims, and a reader who has such a brand in mind applies the triangle to it by requesting the three documents for a lot number, which is a fairer test than any opinion this page could offer. A brand whose entire proposition is purity should sit at every corner it claims with the document in hand, and if it does, the question answers itself for that buyer; if it does not, the reputation was the product.

The worked example is placed at its corners in the open. {FL} sits at the first corner with each batch tested for lead, mercury, arsenic and cadmium by mass spectrometry and the certificate available on request by lot number; at the second with three ingredients, magnesium bisglycinate, an HPMC capsule shell and rice flour as the flow agent, which is the shortest list a machine-filled capsule reaches; and at the third with 1500mg magnesium bisglycinate stated as 300mg elemental at 80% NRV, released against specification. It is UK made under GMP and BRC, 180 capsules for £19.99 at 22p a day. The rice flour is the honest note: it is the excipient that buys the third corner's fill accuracy at the cost of a third item on the second corner's list, and a buyer who wants a two-ingredient capsule wants a slower, dearer fill. The full label breakdown is here.

The verdict: no company has the purest supplements, because pure is three corners and the physics of a capsule keeps any company from sitting at all three on every product. Pick the corner that matters for the product in your hand, metals for minerals and extracts, excipients for intolerances, potency for anything dosed, and request the document that proves it for the lot number on the tub; the brand that sends it is pure in the sense you asked, and the brand that sends a word instead is not.

What to check on the label

Questions people also ask

Which supplement company is the purest?

None sits at all three corners of purity on every product, because pure means three things that pull against each other: free of contaminants, proven by a metals and microbe certificate for the batch; only the active, proven by a short ingredient list; and potent, proven by an assay against the label within tolerance; a capsule with no excipients is harder to fill accurately and an extract with the lowest metals may be diluted to get there, so a buyer picks the corner that matters for the product in hand and requests the document that proves it from the brand, by lot number.

How do I check if a supplement is actually pure?

By corner: for contaminants, email the brand with the lot number on the tub and ask for the certificate of analysis for that batch, which lists each metal and microbial count against its limit with the laboratory's accreditation, and treat a general statement, a different lot or a redacted document as the answer; for excipients, read the ingredient list in descending order of weight and count everything after the active; for potency, ask for the release specification and the batch's assay result against the label.

What does pure mean on a supplement label?

Nothing measurable: pure, clean, nothing artificial and no nasties live at no corner of the purity triangle and are proven by no document, and the claims register that governs health claims does not govern the word pure, so it is used freely; a brand at a real corner says which one and shows the measurement, the metals certificate with figures and limits, the three-item ingredient list or the assay against the label, and the difference between a word and a measurement is the whole test.

Are supplements with no fillers better?

Only at the second corner and at a cost at the third: a capsule with the active and a shell alone is harder to fill accurately on a machine because the powder does not flow evenly without an agent, so a two-ingredient capsule either accepts more variation in fill or pays for a slower fill, and a buyer with an intolerance or an objection to a specific additive has a reason to want the shorter list while a buyer who cares about the dose has a reason to accept a flow agent; the worked example's rice flour is that trade made in the open.

Is this site's magnesium a pure supplement?

At the corners it claims and with the trade-off stated: each batch is tested for lead, mercury, arsenic and cadmium with the certificate available on request by lot number, the ingredient list is three items, magnesium bisglycinate, an HPMC capsule and rice flour as the flow agent, and the 1500mg bisglycinate stated as 300mg elemental at 80% NRV is released against specification; it is UK made under GMP and BRC at 22p a day, and the rice flour is the excipient that buys fill accuracy at the cost of a third item on the list.

Sources

1. The heavy metals analysis literature: inductively coupled plasma mass spectrometry is the standard method for quantifying lead, cadmium, mercury and arsenic in dietary supplements against regulatory maximum levels. PubMed record
2. The pharmaceutical excipient literature: capsule shells, bulking agents, glidants and anti-caking agents, binders, disintegrants and coatings are functional non-active ingredients whose purpose is manufacturability, stability and dosing accuracy rather than effect. PubMed record
3. 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
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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