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Vitamin D is sold in more units, strengths and forms than almost any other single-ingredient supplement. One bottle says 1000 IU. The next says 25 µg. A third says 25 mcg and 125% DV. A fourth, bought overseas, says 10 µg and 200% NRV. They may all be describing the same thing, or four quite different things, and the front of the bottle will not tell you which.
This article is about reading those labels. It covers the unit conversion, the difference between D2 and D3, the difference between an oil capsule and a dry tablet, why strengths differ so much between countries, and what the regulatory numbers on the label mean. It does not tell you how much vitamin D to take and it makes no claim about what vitamin D does for your health. For the evidence background written for an Australian reader, see Vitamin D: what the evidence supports; for supplement labels in general, start with How to Read a Supplement Label.
The conversion you need: 1 microgram = 40 IU
Vitamin D is labelled in two units. International Units (IU) are a biological measure that predates the ability to weigh the vitamin precisely; micrograms (µg or mcg) are simply mass. The U.S. National Institutes of Health Office of Dietary Supplements states the relationship plainly: 1 mcg of vitamin D is equal to 40 IU.
So the conversions that cover almost every product on sale are:
| Micrograms | IU |
|---|---|
| 5 µg | 200 IU |
| 10 µg | 400 IU |
| 15 µg | 600 IU |
| 20 µg | 800 IU |
| 25 µg | 1,000 IU |
| 50 µg | 2,000 IU |
| 100 µg | 4,000 IU |
| 125 µg | 5,000 IU |
Two bottles labelled “25 µg” and “1000 IU” contain the same amount of vitamin D per dose. This is worth stating because the numbers look nothing alike, and a shopper comparing on the front label alone can easily conclude that 1000 is forty times more than 25.
µg versus mcg: the same unit. µg uses the Greek letter mu; mcg is the plain-text version used where the symbol cannot be printed reliably. Neither is more precise.
Why the same product shows different numbers in different countries
Labelling law, not the vitamin, decides which unit appears largest. In the United States, the FDA now requires vitamin D on food and supplement labels to be listed in micrograms per serving, with IU permitted in parentheses; the Daily Value used for the “% DV” figure is 20 mcg (800 IU) for adults and children aged four and over. In the European Union and the United Kingdom, labels use micrograms and express the figure as a percentage of the Nutrient Reference Value, which for vitamin D is 5 µg — so a 10 µg product is labelled “200% NRV”, which sounds dramatic and simply means 400 IU. In Australia, vitamin D supplements are regulated as listed medicines by the Therapeutic Goods Administration and carry an AUST L number on the label; strengths are commonly stated in both IU and micrograms.
The practical consequence: a product bought from an international retailer may carry a different panel from the same brand’s product in your local shop, with a different reference percentage, even when the amount per dose is identical. Read the micrograms or IU, not the percentage.
D2 versus D3: what the label is telling you
There are two forms of vitamin D sold as supplements, and the label will name one of them in the ingredient list.
- Vitamin D3 (cholecalciferol) is the form the skin makes from sunlight and the form found in animal foods. Supplement D3 is most commonly made from lanolin (sheep’s wool grease), which is why most D3 is not vegan; some products now use D3 derived from lichen, and will say so because it is a selling point.
- Vitamin D2 (ergocalciferol) is the plant-and-fungus form, made by exposing yeast or mushrooms to ultraviolet light. It is the traditional vegan option and is also the form in some prescription products.
The two differ chemically only in their side chains, as the NIH fact sheet puts it. The same fact sheet reports that, in the research it reviews, D3 raises and sustains blood 25-hydroxyvitamin D levels to a greater extent than D2. That is a statement about a laboratory measurement, not about any health outcome, and it is included here because it explains why most over-the-counter products are D3 and why D2 products are usually labelled for the vegan market.
What to read: the ingredient list will say “cholecalciferol” or “ergocalciferol”, often with the source (lanolin, lichen, yeast) beside it. If the front says “vitamin D” without a number, the panel settles it.
Capsules, tablets, drops and sprays: the form on the label
Vitamin D is fat-soluble, and the dosage form is one of the more meaningful label choices.
- Oil-filled softgel capsules. The vitamin dissolved in a carrier oil — olive, sunflower, MCT or fish oil are common. The ingredient list names the oil, which matters if you avoid any of them. Softgel shells are usually gelatin (bovine or fish); vegetarian softgels use a plant starch and say so.
- Dry tablets. The vitamin on a powder base with fillers and a binder. Typically the cheapest per dose. The “other ingredients” list will be longer.
- Liquid drops. The vitamin in oil, dosed by dropper. The label states the amount per drop or per millilitre; check which, because a dropper can hold twenty or more drops and “1000 IU per serve” may mean one drop or one dropperful.
- Oral sprays. Dosed per spray. The same caution applies: read the amount per spray and the number of sprays per serve.
- Combination products. Vitamin D is very often combined with calcium, vitamin K2 or magnesium. These are three separate products in one bottle, and each has its own label questions. A D3 + K2 label should give the K2 form (MK-4 or MK-7) and amount separately.
Strength: reading the number in context
Vitamin D products are sold in a wide range of strengths, from 5 µg (200 IU) in multivitamins to 125 µg (5,000 IU) and higher in single-ingredient products. Two regulatory numbers give the label its context, and both come from the NIH fact sheet:
- The Recommended Dietary Allowance for adults is 15 µg (600 IU) a day from age 19 to 70, and 20 µg (800 IU) a day over 70. A product’s “% DV” is calculated against the 20 µg Daily Value, so a 25 µg capsule shows 125% DV.
- The Tolerable Upper Intake Level for adults is 100 µg (4,000 IU) a day. This is the highest daily intake the U.S. Institute of Medicine considered unlikely to cause adverse effects in the general population; it is not a target. Products above this strength are on sale and are generally labelled for use under professional supervision.
None of this tells you what strength to buy. It tells you what the number on the bottle means relative to the reference values a regulator uses, which is what you need to read the label honestly. A health professional who knows your blood results and your medications is the person to ask about the rest.
The rest of the panel
- Serving size. Usually one capsule or tablet, but check: some “1000 IU” products deliver that across two tablets.
- Servings per container. Divide the count on the front by the serving size.
- Other ingredients. The carrier oil, the capsule shell material, any fillers (microcrystalline cellulose, dicalcium phosphate), flow agents (magnesium stearate, silica) and, in chewables, sweeteners and flavours.
- Allergen statement. Fish oil carriers and fish gelatin shells are common and are declared.
- Batch and expiry. Vitamin D in oil is reasonably stable; the expiry date is still the date to read, especially on a bottle bought in a large multipack.
- Regulatory identifiers. An AUST L number on Australian products; a “Supplement Facts” panel format on U.S. products; a “Food supplement” statement on EU and UK products. Each tells you which rules the label follows.
Cost per microgram, and why it is rarely the deciding factor
Vitamin D is one of the cheapest supplements per dose, so the cost arithmetic that decides a protein-powder purchase matters less here. Where it does matter is in combination products and premium forms — vegan D3 from lichen, liposomal formulations, D3 + K2 blends — which can cost many times more per microgram of vitamin D. The method is the same as for any supplement: divide the price by the number of doses, then by the micrograms per dose, and compare like with like.
Checklist before you buy
- Convert the label to one unit: micrograms × 40 = IU.
- Read D2 or D3 in the ingredient list, and the source if it matters to you.
- Read the dosage form and, for drops and sprays, the amount per drop or spray versus per serve.
- Compare the strength with the reference values above so you know what the number means.
- Read the carrier oil, shell material and allergen statement.
- For combination products, read each ingredient’s amount separately.
- If you have a medical condition, take medication, or are already taking a multivitamin that contains vitamin D, check with a pharmacist before adding another product.
Sources
- National Institutes of Health, Office of Dietary Supplements, Vitamin D — Fact Sheet for Health Professionals — for the IU/microgram conversion, RDA, Tolerable Upper Intake Level, Daily Value, U.S. labelling requirements and the D2/D3 comparison as stated.
- U.S. Food and Drug Administration, Dietary Supplement Labeling Guide — for Supplement Facts panel requirements.
- European Union Regulation 1169/2011, Annex XIII — for the 5 µg Nutrient Reference Value used on EU and UK labels.
- Therapeutic Goods Administration (Australia) — for the listed-medicine (AUST L) status of vitamin D supplements sold in Australia.
This article is a guide to reading packaging and comparing products. It is general information only and is not medical advice. It makes no claim that vitamin D benefits any condition, it recommends no dose, and it does not diagnose, treat, or cure any condition. Speak with a qualified healthcare professional before starting any supplement.