How to tell if supplements are good quality in the UK?

The home bench: five tests a buyer runs in ten minutes with a kitchen scale, a glass of warm water and a good light, and the gross failures each one catches

How to tell if supplements are good quality in the UK is a question with two honest answers depending on which bench the buyer is standing at, and the useful thing is to know what each bench can and cannot see. The home bench is a kitchen table, a scale that reads to a hundredth of a gram, a glass of warm water, a good light and ten minutes, and it runs five tests that catch the gross failures, the ones a careless or fraudulent product shows on its surface. Test one is the fill weight: ten capsules are weighed together, the shell weight is subtracted, roughly a tenth of a gram for a size 0 shell and a little more for a 00, and the remainder divided by ten is compared with the stated content per capsule; a magnesium bisglycinate capsule stated at 750mg of compound should weigh about 850mg with its shell, and a tub whose capsules average well under that has been underfilled or has a different content from the one stated, which is the single most common gross failure and the one a scale finds in a minute. Test two is disintegration: a capsule dropped into a glass of water at about body temperature should see its shell soften and open within a few minutes, and an uncoated tablet should break apart within the time the pharmacopoeia allows, around thirty minutes, with gentle swirling; a tablet still whole at the limit has been pressed too hard to dissolve in a stomach and will leave the body much as it entered, which is a failure that a glass of warm water finds and a label cannot. Test three is uniformity: under a good light, the capsules or tablets across the tub should match in colour, size and fill, and the tub should smell of what it is or of nothing, since a fish oil that smells of paint has oxidised, a protein that smells sour has spoiled, and a batch where some capsules are darker than others has been blended badly or mixed from two lots.

Test four is the label against the seven particulars the food supplements regulations require: the words food supplement, the names of the nutrient categories, the portion for daily consumption, a warning not to exceed it, a statement that supplements do not replace a varied diet, a keep-out-of-reach statement, and the amounts per portion, alongside the operator's name and address, an ingredient list, a lot number and a best-before date under general labelling law; a label missing any was written by someone who did not know the regulations, and a product whose makers did not know the regulations is a product whose makers may not know much else. Test five is the arrival check: the seal intact, the lot number and best-before date printed and legible and matching between the tub and any outer box, and the lot number photographed before the tub is opened, since it is what every later question is asked about. Five tests, ten minutes, and a tub that fails any of them is returned under the consumer rights act as not of satisfactory quality or not as described, without the laboratory bench ever being needed; a tub that passes all five has shown that it is not grossly wrong, which is a real result and a limited one.

The laboratory bench: the four tests a kitchen cannot run, the one message that obtains them, what each bench can and cannot see, the worked example across both, and the honest answer

The laboratory bench is where quality in the only sense that matters is decided, and a kitchen cannot run any of its four tests. Identity, that the tub contains the substance on the label and not a cheaper relative, needs chromatography or spectroscopy against a reference standard. Purity, that it contains nothing it should not, needs mass spectrometry for lead, mercury, arsenic and cadmium down to parts per billion, plate culture for microbes, and the specific method for the category's adulterant. Potency, that the labelled amount is present and will still be present at the best-before date, needs an assay at release and a stability study across shelf life, with the overage a competent manufacturer adds so that the label is still true at expiry. Consistency, that this batch matches the last, needs a certificate for every batch against a written release specification. A buyer obtains the laboratory bench by one message quoting the lot number photographed at the arrival check, asking for the certificate of analysis for that batch, and a competent brand sends it within a working day, from a laboratory on the national accreditation register, with the lot number matching, the analytes the category is exposed on listed, and results against limits; a brand that sends a paragraph, a generic certificate, or nothing has failed the laboratory bench by declining to show it, which is as informative as a failed result.

What each bench can and cannot see is the point of setting them side by side. A tub can pass every home test and fail the laboratory bench, since a well-filled, well-dissolving, uniform, correctly labelled, sealed capsule can still contain oxide where glycinate was stated, lead above the limit from a cheap raw material, or a dose that has fallen below the label in the cupboard, none of which has a surface; the home bench rules out the gross and the fraudulent and says nothing about the subtle. The reverse, a tub that fails the home bench and passes the laboratory one, is rare, because a manufacturer that cannot fill capsules evenly or write a compliant label rarely runs an accredited stability programme, which is why the home bench is worth ten minutes as a screen and why its failures are usually final. The worked example is put across both benches in the open: {FL}, capsules whose fill is consistent with 750mg of magnesium bisglycinate each, 1500mg across the two-capsule portion stated as 300mg elemental at 80% NRV; an HPMC shell that opens in warm water within minutes; uniform capsules in a tub that smells of nothing; every mandatory particular on the label with a UK address and operator; a seal, a lot number and a date on arrival; and on the laboratory bench, a certificate of analysis for the lot number testing for lead, mercury, arsenic and cadmium at an accredited laboratory, sent on request, 180 capsules for £19.99 at 22p a day. The honest answer to how to tell if supplements are good quality in the UK is that it takes two benches: ten minutes at the kitchen table on every tub, which catches what is grossly wrong, and one message for the certificate, which decides what the kitchen cannot see, and a buyer who runs the first and sends the second has told as much as can be told without a laboratory of their own.

What to check on the label

Questions people also ask

How can you tell if a supplement is good quality?

At two benches: the home bench, where ten minutes with a kitchen scale, a glass of warm water and a good light runs five tests that catch gross failures, the fill weight of ten capsules against the stated content, the opening of a capsule shell or the breaking apart of a tablet in warm water within the pharmacopoeial time, uniformity of colour, size and smell, the seven mandatory label particulars, and the seal, lot number and date on arrival; and the laboratory bench, where identity, purity, potency and consistency are decided by tests a kitchen cannot run and are read from the certificate of analysis a brand sends when asked for the lot number.

How do I check a capsule's fill weight at home?

Weigh ten capsules together on a scale that reads to a hundredth of a gram, subtract the shell weight, roughly a tenth of a gram for a size 0 capsule and a little more for a 00, and divide by ten to get the average fill, then compare it with the stated content per capsule; a magnesium bisglycinate capsule stated at 750mg of compound should weigh around 850mg with its shell, and a tub whose capsules average well below the stated content has been underfilled or contains something other than what is stated, which is the commonest gross failure and the one a scale finds in a minute.

What is the warm water test for supplements?

A crude imitation of the pharmacopoeial disintegration test: a capsule dropped into a glass of water at about body temperature should see its shell soften and open within a few minutes, and an uncoated tablet, swirled gently, should break apart within about thirty minutes, which is the limit the pharmacopoeia sets; a tablet still whole at the limit has been pressed too hard to dissolve in a stomach and will leave the body much as it entered, a failure a label cannot show and a glass of water can, though the test says nothing about whether what dissolves is the right substance at the right dose.

Can a supplement pass home tests and still be poor quality?

Yes, and this is the reason the laboratory bench exists: a capsule can be well filled, dissolve properly, match its neighbours, carry a compliant label and arrive sealed, and still contain magnesium oxide where glycinate was stated, lead above the limit from a cheap raw material, or a dose that has fallen below the label in the cupboard, none of which has a surface the home bench can see; identity, purity, potency and consistency are read only from the certificate of analysis for the lot number, from an accredited laboratory, which one message obtains from a competent brand within a working day.

What should I do if a supplement fails a home quality test?

Return it: under the Consumer Rights Act 2015 goods must be of satisfactory quality, fit for purpose and as described, with a short-term right to reject within 30 days of delivery and repair, replacement or refund thereafter, and a tub that is underfilled, whose tablets will not disintegrate, whose capsules do not match, whose label lacks the mandatory particulars or whose seal was broken has failed at least one of those; photograph the lot number and the failure, tell the seller which test failed and why, and treat the brand's reply, a lot number request and a named person or a template, as the next test.

Sources

1. The pharmacopoeial disintegration test: uncoated tablets and hard capsules are required to disintegrate in warm aqueous medium within a set time, typically 30 minutes for uncoated tablets and shorter for capsules, the test a tablet pressed too hard to dissolve fails and a kitchen glass of warm water crudely imitates. PubMed record
2. The Food Supplements Regulations' mandatory label particulars: the words food supplement, the names of the categories of nutrients or substances, the portion recommended for daily consumption, a warning not to exceed it, a statement that supplements should not replace a varied diet, a keep-out-of-reach-of-children statement, and the amounts per portion. https://www.legislation.gov.uk/uksi/2003/1387/regulation/7/made
3. The UK and EU guidance on tolerances for nutrition declarations: declared values may deviate from measured values within published tolerance bands, macronutrients by roughly 20% and vitamins and minerals in food supplements by roughly 20% below to 50% above the declared value, with rounding rules for each nutrient. https://www.food.gov.uk/business-guidance/nutrition-labelling
4. The UK Accreditation Service: UKAS accredits testing laboratories to ISO 17025 for defined scopes and publishes a searchable directory of accredited organisations and their schedules of accreditation. https://www.ukas.com/find-an-organisation/

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