The panel on the back of the bottle is a legally defined object with a fixed shape. Learn to read it and you can stand in a shop, pick up a product you have never seen, and know what you are holding.
~13 min read
Pick up any supplement and turn it over. The box on the back is not marketing — it is a legally defined object with a fixed order, a fixed vocabulary and a list of things it is forbidden to say. Once you can read one you can read all of them. The front is where the persuasion lives; the back is where the facts are.
On a product made for the American market it is headed Supplement Facts, and the 1994 regulation that created the category leaves the manufacturer little room.
It looks like the Nutrition Facts panel on a food and does the opposite job: a food panel runs a fixed list whether the nutrients are there or not, while a supplement panel lists only what is in the product. A short panel is a short formula, not a failure to disclose. It must also name the plant part, because a root and a leaf extract of one species are not the same material.
Then what must not appear. No supplement label may claim the product treats, prevents, cures or diagnoses anything. Permitted instead is a statement about structure or function, carried with the notice that the claim has not been evaluated by the regulator. That small print is the exact boundary of the category: a supplement closes a gap in a diet, and replaces neither food nor professional medical care.
Diagram to come
A realistic Supplement Facts panel drawn at readable size, with leader lines out to short annotations around it. The panel itself must be convincing: heavy rule under the heading, serving size and servings per container at the top, then a three-column body — ingredient name, Amount Per Serving, % Daily Value. Show at least one vitamin with its form in brackets, one mineral declared as elemental weight, one botanical with Latin name and plant part, and one row carrying a dagger instead of a number. Below the box, outside it, the Other ingredients line. Annotations point at the serving size, the servings count, a bracketed form, the elemental figure, the %DV column, the dagger and its footnote, and the Other ingredients line. Draw it as a label, not an infographic — the reader must recognise this exact object in their hand.
Which label are you actually holding?
The panel is not identical everywhere, and which system you are in tells you which numbers mean what.
The first line of the panel governs every number under it, and it is the one most often skipped. Every amount in the box is per serving, and a serving is whatever the manufacturer decided — frequently not one capsule.
Four capsules is common in a multivitamin, because a full-spectrum formula will not physically fit in one; two softgels is normal in a fish oil. But a bottle of 120 at four a day is a thirty-day bottle, and at twice daily a fifteen-day bottle — so the shelf price you compared against the bottle beside it was comparing two different things. Do the arithmetic in the aisle: capsules over capsules per serving gives servings, servings over servings per day gives days, price over days gives the only number that matters.
| Bottle A | Bottle B | |
|---|---|---|
| Price | 28.00 | 19.00 |
| Capsules in the bottle | 120 | 60 |
| Serving size | 4 capsules | 1 capsule |
| Days, at one serving daily | 30 | 60 |
| Cost per day | 0.93 | 0.32 |
| Magnesium per serving | 400 mg | 100 mg |
| Cost per 100 mg delivered | 0.23 | 0.32 |
Bottle B looks like the sensible purchase and costs a third as much per day. It is also the more expensive product, because it delivers a quarter of the magnesium. Take the arithmetic one step past cost per day, to cost per unit of what you are buying, and the ranking inverts.
Photograph to come
Two supplement bottles of obviously different sizes held side by side in one pair of hands, both turned so the back panels face the camera and the serving size lines are legible, in real shop lighting with shelving out of focus behind. Brands must not be identifiable — angle, crop or relabel them. The point is the ordinary physical act of comparing two panels while standing up, which is what the section teaches.
The right-hand column gets read as a report card, and it is not one. The percentage is not how much of your requirement the product covers; it is the amount in a serving set against one fixed reference figure, so every product is measured by the same yardstick. One set of figures serves everyone aged four and over — a single number covering a large man and a small elderly woman. It cannot be right for both.
Some rows carry a dagger instead of a percentage, footnoted Daily Value not established: no reference figure exists for that ingredient, as is true of nearly every botanical and of CoQ10.
Neither 100% nor 500% is the answer
One hundred per cent is not a target. The reference figure is set high enough to cover almost everybody, so it sits above what most individuals need — and it is a figure for a whole day from everything, so a supplement showing 100% proposes to supply alone what your food is also supplying. Five hundred per cent is not automatically better: some nutrients have a ceiling, some are simply excreted, and the panel mentions neither.
Those ceilings are where a large percentage becomes a reason to put the bottle down. The fat-soluble vitamins accumulate and are the ones to read when a label is shouting; most water-soluble ones are simply passed. The supplemental magnesium limit of 350 mg is set by a laxative effect, so someone whose magnesium product loosens their digestion has found the dose, not an intolerance. The digestive system explains why.
In the American system the labelling references are the Daily Values, revised in 2016: vitamin C 90 mg, vitamin D 20 mcg, vitamin E 15 mg, magnesium 420 mg, zinc 11 mg, folate 400 mcg, vitamin B12 2.4 mcg. They are drawn from a larger family of figures, and knowing which is which tells you how much weight any of them carries.
Estimated Average Requirement
The amount meeting the needs of half the healthy people in a group, from balance studies and biochemical markers. A median — so half need more.
Recommended Dietary Allowance
That average plus roughly two standard deviations, covering about 97 to 98 per cent of healthy people. Not what a typical person needs — what nearly everyone needs at most.
Adequate Intake
Used where the evidence was too thin to calculate an average requirement: vitamin K, choline, and for a long stretch calcium. An observation of what healthy populations consume rather than a measurement.
Tolerable Upper Intake Level
The highest ongoing daily amount expected to pose no risk to a healthy adult, set from the lowest level at which an unwanted effect appears and divided down by an uncertainty factor. Where none is published, the data is usually missing rather than the ceiling absent.
Daily Value
The labelling figure, and the only one on the panel. Taken from the highest allowance across the groups one label must serve — which is why it sits above most individual requirements.
Most water-soluble vitamins have no ceiling and the excess is passed — riboflavin turning urine bright yellow within the hour is the visible proof. The ones that do have ceilings, worth carrying in your head: preformed vitamin A, 3,000 mcg. Vitamin D, 100 mcg. Niacin as nicotinic acid, 35 mg, above which flushing of the skin becomes common. Vitamin B6, 100 mg. Folic acid, 1,000 mcg — a limit that exists largely because a high intake can obscure a laboratory marker a practitioner uses when checking vitamin B12 status. Iron, 45 mg. Zinc, 40 mg, above which it competes with copper for absorption. Selenium, 400 mcg. Iodine, 1,100 mcg. And magnesium, 350 mg, which applies only to supplemental magnesium and never to magnesium from food.
An individual can sit well away from the labelling figure in either direction, for ordinary reasons. Body size moves nearly every requirement. Absorption changes with age and with stomach acidity, which is why B12 and calcium behave differently at seventy than at twenty. Sun exposure and skin tone change how much vitamin D a body makes for itself. None of which argues for ignoring the percentage — only for reading it as a comparison between products rather than a measurement of you.
What separates someone who can read a label from someone reading the numbers is the short phrase in brackets after most nutrient names, giving the chemical form. It routinely matters more than the figure beside it: two products showing the same milligrams can deliver quite different amounts into a body.
Start with weight. A mineral is never in a capsule alone; it is a salt or a complex bound to something. Magnesium oxide is around 60 per cent magnesium by weight, citrate around 16 per cent, bisglycinate around 14 per cent — so 500 mg of magnesium citrate contains about 80 mg of magnesium. A correct panel declares the elemental amount and puts the compound in brackets: Magnesium (as magnesium bisglycinate) 200 mg means 200 mg of magnesium.
Then the harder version: the densest form is frequently the worst performer. Oxide carries the most magnesium per gram and is cheapest to make, and comparison studies have measured the fraction actually absorbed in single figures — which is why it loosens the bowel so reliably. Magnesium is the clearest case of a principle that generalises: read the bracket, not the number.
| Nutrient | Forms you will see | What the bracket is telling you |
|---|---|---|
| Magnesium | Oxide, citrate, malate, bisglycinate | Oxide is densest and least absorbed; chelates carry less per capsule and get more through. |
| Folate | Folic acid, folinic acid, methylfolate | Folic acid must be reduced by an enzyme first. Methylfolate is already the circulating form. |
| Vitamin B12 | Cyanocobalamin, methylcobalamin, adenosylcobalamin | Cyanocobalamin is the most stable on a shelf and is converted after absorption; the others skip that step. |
| Vitamin E | d-alpha-tocopherol, dl-alpha-tocopherol, tocopheryl acetate | The d- prefix is the natural single form; dl- is synthetic, eight mirror images of which the body retains roughly half. |
Folate is the row worth studying: the panel already admits the forms are not equivalent, declaring micrograms DFE rather than plain micrograms.
Carotenoids are the caution rather than a preference. A plant delivers the family together — beta-carotene, lutein, lycopene — and isolated beta-carotene was studied heavily on the strength of how well carotenoid-rich diets performed, and did not reproduce what the food evidence suggested. A nutrient inside a whole food is not the same intervention as that nutrient alone at a dose no plate delivers, which is Natural Solutions from the other direction.
Diagram to come
Three capsules drawn side by side, identical in physical size, each labelled with a magnesium form. Under each, two stacked bars on one shared scale: how much elemental magnesium the capsule contains, and — visibly different — roughly how much of that is absorbed. The oxide capsule has the tallest content bar and much the shortest absorbed bar; citrate is middling on both; bisglycinate has the shortest content bar and the tallest absorbed bar in proportion. Keep the absorbed bars indicative rather than precisely numbered, and say so in a small note inside the drawing. The one idea the picture must land: the biggest number on the label is not the biggest amount delivered.
Better absorbed is the commonest phrase on the front of a supplement bottle and the least often defined. It has a real meaning, borrowed from pharmacology: bioavailability is the fraction of an administered dose reaching the circulation in a form the body can use. For a nutrient the sentence has to stretch, because the nutrient is already in the body and the body regulates it.
The clean way to measure it is to give a dose, take repeated blood samples over the following hours, and measure the area under the concentration-against-time curve. Two forms tested in the same people give two curves, and their ratio is relative bioavailability — what nearly every absorption claim refers to. The trouble with blood is that it is not an inventory: the body defends a mineral’s blood concentration hard, so a serum reading can look normal while stores are anything at all.
Stable isotope tracers
The dose is made with a rare, non-radioactive isotope — iron-58, magnesium-26, zinc-70 — so what came out of the capsule can be told apart by mass from what was already there. The most rigorous method, and expensive enough to be rare in studies funded to support a product.
Balance studies
Everything in, everything out, over days, with the difference taken as retention. Simple in concept, unpleasant to run, and vulnerable to small errors compounding across a long collection.
Functional markers
Rather than the nutrient, measure something it does — an enzyme whose activity depends on it, or a storage protein. Slower to move and harder to dismiss, because a marker that shifts means the nutrient reached where it works.
Folate is where a panel does the arithmetic for you. A microgram DFE is one microgram from food, 0.6 micrograms of folic acid taken with a meal, or 0.5 micrograms on an empty stomach — folic acid must be reduced by an enzyme before the body can use it, and a common variation in the gene for that enzyme slows the step in a substantial share of people. Which is why methylfolate, already the circulating form, appears increasingly in careful formulas.
The same arithmetic shows up in the units. Vitamin E labels moved from International Units to milligrams, and the conversion is not one number — a milligram of the natural form counted as 1.49 IU, the synthetic as 2.22 IU, which is the numerical expression of the fact that most of the synthetic mixture is not held on to.
Two things follow. Absorption is not fixed: the body raises the fraction it takes up when stores are low, so a form measured in depleted volunteers can look superior and then behave ordinarily in someone already well supplied. And many published comparisons are single small crossover studies funded by an interested party — enough to justify a line on a bottle, not enough to settle a question. So ask what was compared, in whom, and measured how. Better absorbed, with nothing after it, is an adjective.
Somewhere on a good many panels sits a line that reads like an ingredient and behaves like a curtain: Proprietary Blend, followed by a single total in milligrams and a bracketed list of ingredients with no amounts against any of them. That is the largest single red flag on a supplement label, and it is entirely legal.
The rule permits a blend to declare only its total weight, provided the ingredients inside are listed in descending order. That ordering is the only information you get, and it lets you evaluate nothing: a 500 mg blend of eight botanicals cannot be checked against the amounts used in the research the front of the bottle leans on, or set against an upper limit.
The ordering rule is the tell
If a label advertises an ingredient on the front and that ingredient appears last inside a proprietary blend on the back, you have been told what you need to know. The marketable component is the smallest part of the blend, and possibly an amount no study has used.
A good label you will recognise immediately. Every ingredient carries its own amount, botanicals name the species in Latin and the part used, and where the active fraction is standardised the panel names the marker compound and the percentage — turmeric root extract standardised to 95 per cent curcuminoids is a specification, turmeric 500 mg is a word. An amount you cannot see is an amount you cannot judge.
Under the box, outside its border, sits the line headed Other ingredients — everything that is not a dietary ingredient. Fillers, flow agents, binders, disintegrants and capsule shells are ordinary necessities: an ingredient measured in micrograms cannot be made into a tablet alone.
Capsule material
Gelatin is bovine or porcine collagen; vegetable capsules are hypromellose or pullulan. The choice matters for diet and for religious observance.
Colours, sweeteners and flavours
The group worth being selective about. A capsule swallowed whole has no need of a colour.
What is worth avoiding in something taken every day is short: unnecessary colouring, added sugars, hydrogenated oils, undeclared flavouring. Gummies concentrate all of it in one place. This line is also the only place allergens are declared — soy through lecithin or the tocopherols used as a preservative, fish and shellfish with omega-3 oils, wheat in a starch. If somebody in the household avoids one, this is the line that tells you.
In most markets nobody approves a supplement before it goes on sale. The manufacturer is responsible for what the bottle says and enforcement comes afterwards, so the burden of judgement sits with the buyer. Third-party testing is what carries weight: an independent, accredited laboratory tests finished product from a specific batch and states what it found, and a certificate of analysis means something only when its lot number matches the bottle in your hand.
The most useful habit is simply asking. A company that tests every batch will send you the documents; one that tests occasionally sends something dated eighteen months ago for a lot number that is not yours. Both answers are informative, and one email gets you one — the argument the oils side makes in purity and quality.
Two dates appear on supplements and they are not the same claim. An expiry date says the product should not be used afterwards. A best before date is a potency guarantee: the manufacturer undertakes that the amounts in the panel are still there on that date. Passing it ends a guarantee rather than the product.
Oils oxidise, and rancid fish oil smells and tastes of it — the practical test. An enteric coating removes that warning by design, so coated omega-3s should be bought fresh, kept cold and replaced on schedule rather than by nose.
Which makes a bathroom cabinet the worst place in the house, and the shelf above the kettle the second worst. Heat is the variable most under your control, so a cool, dry, dark cupboard is the whole requirement. Fish oils and live cultures go in the refrigerator if the label says so, and the cotton wool comes out once the bottle is opened, since it holds moisture against the contents.
Photograph to come
An ordinary kitchen or bedroom cupboard, opened, with a small number of supplement bottles standing on a shelf — dry, dim, nothing decorative, plainly a real household cupboard rather than a styled pantry shot. The room beyond should read as not-a-bathroom. One bottle carries a handwritten opened-on date on the label. The picture makes one point: the right place is dull, dry and away from heat.
Everything above is one procedure, and it takes about ninety seconds once familiar. Here it is on a bottle nobody has told you anything about: a multivitamin, 120 tablets, 29.99, confident front label, unread back.
The conclusion is rarely that a bottle is bad. It is that you know what it is, what it costs a day, which forms it uses and what it has declined to tell you. Run it on what you already own: the panels on Microplex VMz, xEO Mega and PB Assist+ answer the same questions as anything else on a shelf, and which products are available differs by country. A panel describes a product, not a diet: nothing in a capsule replaces food, and nothing here replaces professional medical care, the argument Why Supplement makes.
Supplements are intended to complement a varied diet, not to replace one. If you are pregnant, nursing, under medical care or taking medication, speak to your healthcare practitioner before starting anything new, and keep supplements out of reach of children. Nothing here is intended to diagnose, treat, cure or prevent any disease.
The skill is portable, which is why it comes before any specific product.
Lesson 3 of 12 · Nutrition