How to read a supplement label?

The label gives enough numbers to check itself: the first sum, days and pence, which is the only price on the shelf, and the second sum, elemental over compound, which catches the front-of-label figure sold as a dose

How to read a supplement label is a question usually answered by walking through the label's lines, and the lines are worth knowing; but the thing that separates a buyer who reads labels from one who looks at them is arithmetic, because a UK supplement label is required to give enough numbers that it can be checked against itself, and almost nobody does the checking. Three sums use only the numbers printed on the tub, take a minute with a phone, and between them catch most of what a misleading label does. The words on the label, the ingredients, the warnings, the operator, are read after the sums, because the sums decide whether the words are worth reading.

The first sum is days and pence. The label states the number of capsules, tablets or grams in the tub and the number per daily dose as recommended on the label, and dividing the first by the second gives the number of days the tub lasts; dividing the price by that number gives the cost per day, which is the only price on the shelf that compares one tub with another. The shelf prices by the tub, and tubs differ in count, in capsules per dose and in dose per capsule, so that a cheaper tub is often the dearer product; a tub of sixty capsules at three a day is twenty days, a tub of one hundred and eighty at two a day is ninety, and a price that is twice as high for the second tub is a cost per day less than half. A buyer who does the first sum on two tubs has priced them correctly, and a buyer who reads the shelf price has not priced them at all. The same sum reveals the serving-size trick, in which a label states a small dose per capsule and a daily dose of four or six, so that the tub which looks like two months is three weeks.

The second sum is elemental over compound, and it catches the commonest mislead on a mineral label. The front of the tub states a weight of the compound, magnesium bisglycinate 1500mg, zinc picolinate 50mg, and the nutrition panel on the back states the elemental mineral, the magnesium or zinc itself, which is the dose the body receives and the figure the reference value and the upper level are set for. The two are related by chemistry: each form carries a fixed share of its weight as the mineral, roughly a fifth for magnesium bisglycinate, around three fifths for magnesium oxide, around a seventh for zinc picolinate, and dividing the panel's elemental figure by the front's compound figure must give that share. A label on which the sum works has told the truth twice; a label on which the front's compound figure is the only figure, or on which the panel's figure is the compound figure repeated, has sold the buyer the weight of the salt as if it were the dose, which can overstate the mineral by five times. The sum takes ten seconds once the share for the form is known, and the previous pages in this section list the common shares.

Two sums done, with the third, the reference value back-check, the words read after the sums, the worked example's label run through all three and the verdict in the next section.

The third sum, the reference value back-check, and what a mismatch means; the words read after the sums, the ingredients, the warnings and the operator; the worked example's label run through all three; and the verdict

The third sum is the reference value back-check, and it confirms the second from the other direction. A UK label must state each vitamin and mineral per daily dose and as a percentage of the nutrient reference value, and the two figures were printed from each other: the reference value for magnesium is 375mg, so a label stating 80% must be stating 300mg elemental, and a label stating 300mg must be stating 80%. Multiplying the reference value by the percentage gives the elemental figure, and a buyer who knows a handful of reference values, 375mg magnesium, 10mg zinc, 14mg iron, 5 micrograms vitamin D, 2.5 micrograms B12, can run the sum on any tub. A mismatch between the percentage and the elemental figure is a labelling error, and a label with one error is read for others; a percentage that is high, several hundred percent, is not an error but a flag to look up the upper level for that nutrient, since the label does not print it. A label whose three sums agree has told the truth in three places, and its words can be read with some confidence.

The words come after the sums. The ingredients list, in descending order of weight, gives the form of each nutrient, which the second sum needed, and the excipients after the actives, which are counted, since a short list is a formulation decision and a long one a manufacturing convenience; the allergens are emphasised within it. The recommended daily dose and the two mandatory statements, not to exceed the stated dose and that a supplement is not a substitute for a varied diet, are required and their absence is a label that has not been done to the UK rules. The warnings specific to the product, the pregnancy line, the medicine line, the under-eighteen line, are read and, for anyone they apply to, acted on with a pharmacist or a doctor. And the name and address of the responsible operator, UK or EU, closes the read, because a label with no operator has nobody answering for its numbers.

The worked example's label is run through all three sums and read for its words: {FL} states 180 capsules and two per daily dose, which is ninety days, and £19.99 over ninety days is 22p a day, the first sum; it states 1500mg magnesium bisglycinate on the front and 300mg elemental magnesium on the panel, and 300 over 1500 is one fifth, the share the chemistry allows for bisglycinate, the second sum; and it states 80% of the nutrient reference value, and 375mg times 80% is 300mg, the third sum. Its ingredients list reads magnesium bisglycinate, the HPMC capsule shell and rice flour, two excipients after the active; it carries the recommended dose, the two mandatory statements and the warnings; and it names a UK responsible operator with an address. It is batch tested for lead, mercury, arsenic and cadmium, UK made under GMP and BRC. The full label breakdown is here.

The verdict: read a supplement label by doing the three sums it invites. Capsules in the tub over capsules per dose gives days, and price over days gives the cost per day, the only price that compares tubs. Elemental over compound must give the share the form's chemistry allows, which catches the front-of-label weight sold as a dose. The reference value times the percentage must give the elemental figure, which confirms the panel from the other side and flags a high dose for an upper-level check. Then read the ingredients for form and excipients, the dose and the warnings, and the operator's address. A label whose three sums agree has told the truth in three places, and a label that fails one is read for what else it got wrong.

What to check on the label

Questions people also ask

What should I look for on a supplement label?

Three sums before any words: capsules in the tub divided by capsules per daily dose for the days it lasts and the price divided by that for the cost per day, the only figure that compares two tubs; the elemental figure on the panel divided by the compound weight on the front, which must equal the share the form's chemistry allows and catches a compound weight sold as a dose; and the nutrient reference value multiplied by the percentage on the panel, which must give the elemental figure; then the ingredients list for the form and the excipient count, the recommended dose and the mandatory statements, the warnings, and the responsible operator's name and UK or EU address.

What is the difference between the amount on the front and the amount on the back of a supplement?

The front usually states the weight of the compound, the mineral bound to whatever carries it, such as 1500mg magnesium bisglycinate, and the panel on the back states the elemental mineral, the magnesium itself, which is the dose the body receives and the figure the reference value and the upper level are set for; the two are related by a fixed share for each form, roughly a fifth for bisglycinate and around three fifths for oxide, so dividing the panel's figure by the front's must give that share, and a label on which the front's compound weight is the only figure, or is repeated on the panel, has overstated the dose by up to five times.

What does the percentage on a supplement label mean?

The share of the nutrient reference value that the daily dose supplies, printed from the elemental figure so that the two can be checked against each other: the reference value for magnesium is 375mg, so 80% means 300mg elemental and a label stating one must state the other; a mismatch is a labelling error and a label with one error is read for others, while a very high percentage, several hundred percent, is not an error but a flag to look up the nutrient's upper level, which the label does not print and which differs widely between nutrients, before deciding whether the dose is a correction or an excess.

How do I work out the cost per day of a supplement?

Divide the number of capsules, tablets or grams in the tub by the number per daily dose as recommended on the label to get the days the tub lasts, then divide the price by the days: a tub of one hundred and eighty capsules at two a day lasts ninety days and £19.99 over ninety days is 22p a day, while a tub of sixty at three a day lasts twenty and a lower shelf price can be a higher cost per day; the shelf prices by the tub and tubs differ in count, capsules per dose and dose per capsule, so the cost per day is the only price that compares two products, and it takes ten seconds with a phone.

Does this site's magnesium label pass the three sums?

Yes, and the figures are on the tub: 180 capsules at two per daily dose is ninety days and £19.99 over ninety days is 22p, the first sum; 1500mg magnesium bisglycinate on the front and 300mg elemental magnesium on the panel give one fifth, the share the chemistry allows for bisglycinate, the second; and 80% of the 375mg nutrient reference value is 300mg, the third; the ingredients list reads magnesium bisglycinate, the HPMC capsule shell and rice flour, the label carries the recommended dose, the mandatory statements and the warnings, and a UK responsible operator's address closes the read, with each batch tested for four metals and UK manufacture under GMP and BRC.

Sources

1. 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
2. The Food Supplements (England) Regulations 2003 (food supplements are regulated as foods in the UK). https://www.legislation.gov.uk/uksi/2003/1387/contents/made
3. The vitamin and mineral form literature: magnesium oxide has lower fractional absorption than citrate or glycinate; synthetic DL-alpha-tocopherol has about half the biological activity of the natural RRR form per milligram; cyanocobalamin and methylcobalamin both correct B12 deficiency; form changes absorption or activity per milligram rather than whether a nutrient works. PubMed record
4. Retained Regulation (EC) No 1924/2006 on nutrition and health claims made on foods, and the Great Britain nutrition and health claims register. https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register

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