Vitamin D supplements look alike on the shelf, but they differ in three ways that matter: the form of vitamin D (D3 or D2), the amount per serving, and the format, such as capsules, softgels, drops or chewables. Once you can read those three things on a label, comparing products becomes much easier.
This guide is general information, not medical advice. How much vitamin D you need depends on your age, diet, sun exposure, health and any medicines you take. If you are pregnant, breastfeeding, buying for a child, taking prescription medicines or have a medical condition, talk to a doctor or pharmacist before you start a supplement. A doctor can also arrange a blood test if you want to know your actual vitamin D level.
The short version: most products contain vitamin D3, most adults who choose to supplement pick a modest daily amount within the reference ranges below, and more is not better. Vitamin D is fat soluble, so the body stores it, and very high intakes over time can cause harm.
D3 or D2: what is the difference
There are two main forms in supplements:
- Vitamin D3 (cholecalciferol): the form the skin makes in sunlight. In supplements it usually comes from lanolin (sheep’s wool) or, in vegan products, from lichen.
- Vitamin D2 (ergocalciferol): made from plant sources and yeast, and often found in vegan products and some fortified foods.
According to the US National Institutes of Health Office of Dietary Supplements (NIH ODS), both forms raise vitamin D levels in the blood, but D3 may raise them higher and keep them up for longer. That is one reason most of the vitamin D range is D3. If you follow a vegan diet, check the label: standard D3 is not vegan, while lichen-based D3 and D2 are.
Reading the dose: IU and mcg
Labels show vitamin D in micrograms (mcg), international units (IU) or both. The conversion is simple: 1 mcg equals 40 IU.
| mcg | IU | Typical use on labels |
|---|---|---|
| 10 mcg | 400 IU | Infant drops, some multivitamins |
| 15 mcg | 600 IU | Many adult multivitamins |
| 25 mcg | 1,000 IU | Common single-ingredient capsules |
| 50 mcg | 2,000 IU | Common higher-strength products |
| 125 mcg | 5,000 IU | High strength, above the adult upper limit |
| 250 mcg | 10,000 IU | Very high strength, for use under medical advice |
NIH ODS lists these reference amounts from all sources combined, food and supplements:
- Recommended amount (RDA): 400 IU (10 mcg) for infants, 600 IU (15 mcg) for ages 1 to 70, and 800 IU (20 mcg) for adults over 70.
- Upper limit: 4,000 IU (100 mcg) a day for adults and children aged 9 and over, with lower limits for younger children.
Many products on the market, including some in this range, contain 5,000 IU or 10,000 IU per serving. Those amounts are above the adult upper limit and are normally used only when a doctor recommends it, for example to correct a measured deficiency. If you take a multivitamin as well, add up the vitamin D from both so you know your total.
Choosing a format
The best format is the one you will take consistently and that suits the person taking it.
| Format | Good for | Things to check |
|---|---|---|
| Capsules and tablets | Simple daily use | Capsule size, vegetarian or not |
| Softgels | Vitamin D already in oil | Usually gelatin, so not vegetarian |
| Liquid drops | Flexible doses, people who dislike pills | IU per drop, not per bottle |
| Chewables and gummies | Those who cannot swallow pills | Sugar, sweeteners, keep away from children |
| Combinations (D3 with K2, calcium or zinc) | People already advised to take both | Dose of each ingredient |
A plain capsule such as Bluebonnet Vitamin D3 1,000 IU shows the simplest option. Softgels like Natural Factors D3 2,000 IU come in oil. Drops such as Bluebonnet Liquid Vitamin D3 let you adjust the amount, but read the label carefully, because the stated strength is per serving, which may be one drop or several. Chewables such as Bluebonnet Earth Sweet D3 suit people who struggle with pills.
Vitamin D with K2 or calcium
Some products combine vitamin D3 with vitamin K2 or calcium. These combinations make sense only if you have been advised to take both nutrients. Vitamin K can interact with blood thinners such as warfarin, so anyone on those medicines should speak to their doctor before taking a product that contains vitamin K. You can find K products in the vitamin K category.
How to take it
Because vitamin D is fat soluble, NIH ODS notes that it is absorbed better when taken with a meal or snack that contains some fat. Many people simply take it with breakfast or dinner. Daily use is the most common pattern on labels.
Some practical points:
- Take it at the same time each day so it becomes routine.
- Store it in a cool, dry place out of direct sunlight.
- Keep all supplements, and especially chewables and gummies, out of reach of children.
- Check the expiry date and the number of servings per bottle when comparing prices.
- Look for third-party testing seals if quality assurance matters to you.
For more on keeping supplements in good condition, see the blog post on storing vitamins and supplements, and the guide to vitamin B12 supplements.
Safety: when more is not better
Vitamin D toxicity is rare and almost always comes from taking high-dose supplements for a long time, not from food or sunlight. NIH ODS describes symptoms such as nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, frequent urination, thirst and kidney stones, caused by too much calcium in the blood.
Vitamin D can also interact with some medicines, including certain steroids, the weight-loss drug orlistat and some cholesterol and blood pressure medicines. Tell your doctor or pharmacist about every supplement you take, including those in a multivitamin from the multivitamins range.
Quick checklist
- Check the form: D3 or D2, and vegan or not.
- Read the dose in IU or mcg; 1 mcg is 40 IU.
- Stay within the reference ranges unless a doctor advises otherwise.
- Add up vitamin D from every product you take.
- Choose a format you will take every day.
- Take it with a meal that contains some fat.
- Ask a doctor or pharmacist first if you take medicines, are pregnant or are buying for a child.
Common questions
Should I take vitamin D every day?
Many products are designed for daily use, and NIH ODS gives its reference amounts per day. Whether you need a supplement at all depends on your diet, sun exposure and health, so ask a doctor or pharmacist if you are unsure.
Is 5,000 IU a day too much?
It is above the 4,000 IU daily upper limit that NIH ODS gives for adults. Higher doses are sometimes prescribed for a limited period to treat a deficiency, but that should be decided and monitored by a doctor.
Can I get enough vitamin D from food?
Few foods are naturally rich in vitamin D. Oily fish, egg yolks and fortified foods such as some milks and cereals contribute, and the skin makes vitamin D in sunlight. How much you get from these depends heavily on where you live and the time of year.
