How to Read a Supplement Label

The serving size sits at the top of the Supplement Facts panel, and every amount below it is per serving. FDA defines a supplement's serving size as the most the label tells you to take at one time. If the directions say "take 1 to 3 capsules with breakfast," the serving is 3 capsules, and the numbers on the panel describe all three. (FDA's own labeling guide uses the same example, with tablets.) A label may add a per-capsule column, but it doesn't have to.

So before you compare two products, put them on the same footing. A two-capsule serving and a one-capsule serving can hold the same 500 mg; the first just asks you to swallow more. The next line, servings per container, tells you how many full servings the bottle holds.

Each dietary ingredient on a Supplement Facts panel gets its own line, usually with its weight per serving in grams (g), milligrams (mg) or micrograms (mcg). A microgram is a thousandth of a milligram, so 400 mcg and 400 mg sit a thousandfold apart and one letter apart. Read the unit twice.

The weight on that line belongs to the nutrient itself, and the compound carrying it weighs more. "Calcium 500 mg (as calcium carbonate)" means 500 mg of calcium. NIH's Office of Dietary Supplements (ODS) puts calcium carbonate at 40% calcium by weight and calcium citrate at 21%. So 500 mg of calcium takes about 1,250 mg of calcium carbonate, or about 2,400 mg of calcium citrate. That gap is one reason two calcium products with the same 500 mg on the label can come as very different amounts of powder.

The % Daily Value (%DV) column compares one serving with a reference amount FDA sets for each nutrient. The math is the amount per serving divided by the Daily Value, times 100. FDA's Daily Value for calcium is 1,300 mg, so a serving with 500 mg of calcium shows as 38%. FDA's rule of thumb: 5% DV or less per serving is low, and 20% or more is high.

The Daily Value is one number for the general population, so it can't tell you what you personally need, or how much is too much. For the upper end, ODS fact sheets list a nutrient's Tolerable Upper Intake Level (UL), the highest daily intake unlikely to cause harm. A %DV far above 100 isn't automatically good or bad. The UL is the number to check.

Herbs, amino acids and most specialty ingredients have no Daily Value. Next to them you'll see a symbol, such as an asterisk, pointing to the footnote "Daily Value not established." The footnote means there's no federal reference amount for that ingredient, so its weight per serving is the only number you get. That's why a label that hides the weight, as a proprietary blend does, costs you so much (Why Proprietary Blend Doses Matter).

Many nutrients come in more than one chemical form. The label names the form in parentheses after "as" or "from," as in "Calcium (as calcium citrate)." If the form isn't named there, it has to appear in the ingredient list below the panel.

Forms behave differently in the body. ODS notes that calcium citrate depends less on stomach acid than calcium carbonate does, so it can be taken without food. A few nutrients even get their own unit for this reason. Folate is listed in mcg DFE (dietary folate equivalents), a unit that adjusts for how well each form is absorbed, and FDA counts each microgram of added folic acid as 1.7 mcg DFE. When folic acid is added, its own weight appears in parentheses: "Folate 680 mcg DFE (400 mcg folic acid)." The Daily Value is 400 mcg DFE, so that line shows 170%. Same 400, different units.

A botanical listed on a supplement label has to name the part of the plant it comes from: root, leaf, seed, bark or flower. Of all the labeling rules, this is the one I'd defend hardest. Different parts of one plant can contain different compounds, and Chinese herbal medicine treats some of them as separate herbs. The cassia tree gives two: its twig is gui zhi and its bark is rou gui. A label that lists an herb with no plant part is missing something the rule requires. Many labels also give the Latin name, which settles which plant it is.

Extracts carry more fine print. A label may give a ratio such as 4:1, which usually means four parts of plant went into one part of extract, and may name the solvent, such as water or ethanol. When the solvent has been removed, the weight listed is the weight of the dried extract. Some labels add a line like "equivalent to 1,000 mg of dried root." Read that line as history: it describes the plant that went into the extract. What's in the capsule is the extract weight on the panel, and that's the number to hold up against research that used the same kind of extract.

A supplement's ingredient list sits just below the Supplement Facts panel. When the panel has already named its ingredients and their sources, this list is headed "Other ingredients" and covers the rest of the product: capsule shells, fillers, flow agents, colors, flavors, sweeteners. Like a food ingredient list, it's ordered by weight, heaviest first. If you avoid gelatin, soy or a particular dye, this is where to look.

Then find the company line. The label must name the manufacturer, packer or distributor and its place of business. "Manufactured for" or "Distributed by" means the company on the front didn't make the product; a contract manufacturer did. That arrangement is common and allowed, and it hands you a good question for any brand: who makes it? The label must also give a US address or phone number for reporting serious adverse events, meaning serious reactions to the product.

Any claim about how an ingredient affects the body's normal structure or function must carry this disclaimer, word for word: "This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease." With several claims, the label may use the plural: "These statements have not been evaluated…" An asterisk usually links each claim to it.

FDA calls these structure/function claims. Its own examples are "calcium builds strong bones" and "fiber maintains bowel regularity." Nobody at FDA signs off on them first. The company must have evidence that each claim is truthful and not misleading, and must notify FDA of the claim within 30 days of first marketing the product with it. Outside narrow exceptions, such as FDA-authorized health claims, a supplement can't claim to diagnose, treat, cure or prevent a disease.

So the disclaimer tells you who stands behind the claim: the company, with no review by FDA. That doesn't make the claim false, and it doesn't make it proven. When I see the asterisk, I take it as a prompt to ask the company what its evidence is.

A supplement label is the company's account of what's in the bottle. Whether your bottle matches it takes a lab test of that lot, and What a Certificate of Analysis Tells You shows how to read the report. A label also can't give you the individual doses inside a proprietary blend, since the rule lets the company leave them out. Why Proprietary Blend Doses Matter shows how to estimate them.

Read a few panels this way and you'll start to notice which labels hand you every number, and which ones make you work for it.