Methodology

The source

The Dietary Supplement Label Database (DSLD) is kept by the NIH Office of Dietary Supplements. It transcribes the labels of dietary supplements sold in the United States: the Supplement Facts panel row by row, the other ingredients, the statements (directions, warnings, claims, seals), the manufacturer and the dates a label entered the database and, where known, left the market. We use its full download, version 9.4.0, downloaded by NIH on January 10, 2026: 214,780 labels, the newest entered on September 25, 2025. The file is archived unchanged, and every page links the NIH record of its label.

From labels to products

A product is sold in several sizes, label designs and versions, each a separate DSLD label. We group labels that share a product name and a brand, ignoring letter case and punctuation, into one product: 214,780 labels become 116,682 products. A product's current label is its newest label still on the market (or its newest label when all are off the market), and the product page reads that label; every other label of the product is listed with its dates. Brands are grouped the same way into 5,741 brands.

From label rows to ingredients

DSLD names each row as the label prints it and assigns an ingredient group. We fold spelling variants of a group together and gather the forms of a nutrient into one ingredient: thiamin and vitamin B1, folate and folic acid, vitamin D2 and D3. That turns 5,411 DSLD group names into 4,053 dietary ingredients and 496 other ingredients (fillers, capsule materials, flavours). The chemical form a label names (magnesium glycinate, methylcobalamin) is kept, and the 72 most-listed forms have their own pages. Each ingredient keeps the kind DSLD records for it (vitamin, mineral, botanical, probiotic strain, amino acid and so on); because every strain or herb is its own ingredient, list pages also count how many products list at least one ingredient of each kind (below). Spellings DSLD keeps apart for one ingredient ("Magnesiium", "Coenzyme Q-10" beside "Coenzyme Q10") are folded into the commonest spelling. A mineral row named as its compound ("Magnesium L-Threonate 2,000 mg") usually states the compound's weight, so it is not counted as the mineral when the label gives the element; a row named "Elemental" is the mineral's amount.

How kinds are counted

A list page's kinds chart counts each product once per kind: a product listing three probiotic strains and vitamin D counts once for probiotic strains and once for vitamins. Only dietary ingredients count; rows from the Nutrition Facts part of the panel (calories, fat, cholesterol, carbohydrate, fiber, sugars, protein, sodium) and blend headers do not. The share is the number of products listing at least one ingredient of the kind, divided by the products on the list.

Amounts

Amounts are compared only in the same measure. Weights are converted to milligrams. Vitamin D in IU is converted at 40 IU per microgram, the equivalence the Institute of Medicine states (2011). Vitamin A in RAE, folate in DFE, vitamin E in IU and other units are compared only with amounts in the same unit, because their conversion depends on the form. An amount is per serving as the label states it; the amount per day multiplies it by the largest number of servings a day the label's directions allow, or one serving when the label states none. A row inside a proprietary blend with no amount of its own is shown as not disclosed.

Each ingredient's distribution (the 10th, 25th, 50th, 75th and 90th percentiles of amounts per serving) is computed over the current labels of every product that gives an amount in the common measure. A product page draws each amount on that distribution, and its rank says how many products list more. Percentiles from the 10th to the 90th are not moved by the few transcription or unit slips at the extremes.

An amount enters a distribution, a rank, a median, a count above the upper limit or a named list only when it is plausible: it lies between the lowest and highest 0.2% of the ingredient's amounts (the same bounds for every label), it is under 50 times the adult upper limit where one exists, the %DV the label prints agrees with it against the current Daily Value or the one in force before the 2016 revision (21 CFR 101.9, 2015 edition), not more than five times off and not 0% beside an amount worth 5% or more of the Daily Value, and it is not the weight of a mineral compound. Inside those bounds, an amount above the 99th percentile of a nutrient with a Daily Value must also be backed by the label: a printed %DV that agrees with it, or the same strength in the product's name ("Vitamin D3 50,000 IU"). The 50,000 IU vitamin D products pass; a 5,000 mcg vitamin D row on a product that prints neither does not. For an ingredient without a Daily Value, an amount above the 99th percentile and more than ten times the 90th must carry its strength in the product's name. A product with an implausible amount still counts as listing the ingredient, and its page says the amount looks like a transcription slip.

Reference values

Daily Values for 27 nutrients come from 21 CFR 101.9(c)(8)(iv), adults and children 4 years and older, and for pregnancy and lactation where the regulation gives them. Adult Tolerable Upper Intake Levels for 23 nutrients come from the Institute of Medicine's Dietary Reference Intakes summary tables (2011), with the part of intake each covers (for magnesium, supplements only; for niacin and folic acid, the synthetic forms). The saved texts of both sources are checked on every build; a value missing from them stops the build.

Comparisons

• Closest formulas. Two products are compared by the ingredients they share, each ingredient weighted by how rare it is across the database (a shared rare ingredient counts for more than shared vitamin C); the similarity is 1 for the same list, whatever the amounts. Among products with the very same list, the ones whose amounts are closest come first. A product page lists up to six products with a similarity of 0.35 or more.
• Lists. 198 lists (categories, who a product is for, diets, physical forms, seals and forms of a nutrient) are defined by rules over the label data. Each list page states its rule in plain words. A list of an ingredient in one physical form or for one group (vitamin C powder, magnesium for women) takes products where the ingredient is primary: the product name names it, or the label lists at most three dietary ingredients and gives the ingredient at its common dose or more (the lower quartile of all products listing it).
• Analyses. Each of the analyses states its own method and limits and publishes its figures as a CSV.

Limits

• The data is what labels state, as transcribed by NIH. Nobody here tests products, and a label claim (a seal, a "gluten free") is the label's claim.
• DSLD aims to cover supplements sold in the United States but is not a complete register; coverage has grown since 2011, and a product missing here may still be sold.
• A label can change after it was transcribed. The page shows the date of the label it reads; the package is the authority.
• Transcription slips happen. Where a label prints a %DV that disagrees with the amount by more than five times against both the current and the pre-2016 Daily Value, the amount is left out of every figure; a reader who finds a slip can report it.
• A comparison with the Daily Value or the upper limit describes a label, not a person's intake from food and other products. It is not medical advice; what each nutrient does and how much a person needs are in the NIH Office of Dietary Supplements fact sheets.

Who reviews the pages, and when

Before each release, three figures on every page type (products, brands, ingredients, lists and the research pages) are checked against the NIH label database records they cite, and the pages are read in separate review passes against Google's and Bing's published quality guidelines, for claims a brand or a reader could dispute, and for any figure that reads differently on two pages. The studio runs these checks with AI tools and records each one; the last full review was for the release of October 8, 2026. PlainVitamins publishes what labels state, not health advice: a label is the manufacturer's claim, and a doctor or pharmacist, with the product's own label, is the authority for what to take.

Updates

When NIH publishes a new full release of the database, it is loaded, checked against the previous one and recorded in the changelog; product addresses stay the same from release to release.