How to Choose a Vitamin D3 Supplement
On a supplement shelf, "vitamin D" can mean two different forms. For a daily supplement, vitamin D3 is the better-supported choice, and here is how to pick a good one.
Last reviewed: October 2026 · How we research
Disclosure: As an Amazon Associate I earn from qualifying purchases. This guide is general information, not medical advice. Talk to your doctor before starting any supplement.
D3 or D2? Look for the "3"
Vitamin D supplements come in two forms: vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). A label that only says "vitamin D" does not tell you which one is inside, so check the Supplement Facts panel. The NIH Office of Dietary Supplements reports that research shows vitamin D3 raises blood levels of vitamin D (measured as 25(OH)D) to a greater extent than vitamin D2, and that D3 can maintain those higher levels for longer. Both forms do raise blood levels, but D3 is the better-supported choice for a daily supplement, which is why the shopping links on this site search for D3.
- Standard D3 is typically made from lanolin, a substance obtained from the wool of sheep, so many D3 products are not vegan.
- Vegan D3. An animal-free D3 made from lichen is also available. Look for "vegan D3" or "from lichen" on the label.
- D2 is made by exposing a compound in yeast to ultraviolet light. If you avoid animal products, you can also contact supplement makers and ask how their vitamin D is sourced and processed.
Check the label
- Units. Labels may list IU, mcg, or both. One microgram (mcg) equals 40 IU, so 25 mcg is 1,000 IU. Make sure you are comparing like with like.
- Dose per serving. Products range from modest daily amounts to very high-dose capsules meant for occasional use. Do not assume bigger is better.
- Other ingredients. Some products add vitamin K2 or calcium. That is a choice to make with your doctor, not by default.
- Third-party testing. Look for seals from USP, NSF, or similar independent labs.
Pick a form you will actually take
- Softgels: Vitamin D3 is fat-soluble and is often sold in oil, which is convenient.
- Drops: Good if you have trouble swallowing pills, and the dose is easy to adjust.
- Gummies: Pleasant to take but may contain sugar, and the amount per gummy can vary more than in other forms.
Good habits
- Take it with a meal that contains some fat, which helps absorption.
- Take it at the same time each day so it becomes routine.
- Store it away from heat and moisture.
Talk to your doctor about the dose
Your needs depend on things like diet, sun exposure, skin tone, age and where you live. A simple blood test (25-hydroxyvitamin D) can show where you stand, and NIH describes a level of 20 ng/mL (50 nmol/L) or higher as adequate for most people. Your doctor can interpret your result. The NIH Office of Dietary Supplements lists 100 mcg (4,000 IU) a day from all sources, including food and supplements, as the upper limit for adults, because too much vitamin D over time can cause problems. Doctors sometimes recommend higher amounts for a limited time to treat a deficiency, which is a decision to make with your doctor. Some medicines can interact with vitamin D, including statins, thiazide diuretics, orlistat and steroids such as prednisone, so tell your doctor or pharmacist about everything you take.
How US and UK guidance differ
Official advice on amounts is not the same everywhere, so numbers you see in one country may not match another. Neither is a prescription for you.
- United Kingdom. According to the NHS, children from age 1 and adults need 10 micrograms (400 IU) a day. Government advice there is that everyone should consider a daily supplement during autumn and winter, because from about late March or early April to the end of September most people can make what they need from sunlight. The NHS says people at higher risk of not getting enough, including people with dark skin and people who are rarely outdoors, should take a supplement all year round, and that adults should not take more than 100 micrograms (4,000 IU) a day.
- United States. The recommended amount is 600 IU (15 mcg) a day for most adults up to age 70 and 800 IU (20 mcg) after that, with 4,000 IU a day from all sources as the upper limit for adults, according to NIH and MedlinePlus.
The numbers differ, and so does the thinking behind them, such as how much sun people in each country get. Your doctor can tell you what fits your situation, ideally with a blood test.
What about vitamin K2?
Many D3 products add vitamin K2, and it is reasonable to ask about it. Here is what the NIH says. Vitamin K comes as K1 (phylloquinone) and K2 (menaquinones such as MK-4 and MK-7). K2 is found in fermented foods and foods from animals. Vitamin K is important for healthy bones, but the NIH says research on vitamin K supplements for bone strength is mixed and more is needed. It does not say that K2 must be taken with D3, only that some supplements combine them.
- Warfarin (Coumadin) and other blood thinners. The NIH warns that vitamin K can have a serious interaction with warfarin, and that a sudden change in the amount of vitamin K you get can cause dangerous bleeding. If you take a blood thinner, do not start a D3 + K2 product without your doctor.
- Check the label. Look for the form (MK-4 or MK-7) and the amount in micrograms. The adequate intake is 120 mcg a day for adult men and 90 mcg for adult women, from all sources.
- Soy. If you avoid soy, ask the maker where the K2 comes from and what the other ingredients are.
- If you decide on a combination, search Amazon for D3 + K2 supplements.
Sources and further reading
We read these pages in October 2026. They come from government health agencies in the United States and the United Kingdom and are not affiliated with this site. Where official advice differs between countries, we say so in the guide. Always follow the advice of your own doctor or pharmacist.
- NIH Office of Dietary Supplements: Vitamin D, consumer fact sheet (page dated November 2022)
- NIH Office of Dietary Supplements: Vitamin D, health professional fact sheet (read October 2026)
- NIH Office of Dietary Supplements: Vitamin K, consumer fact sheet (read October 2026)
- NHS (United Kingdom): Vitamin D (read October 2026)
- MedlinePlus en español (U.S. National Library of Medicine): Vitamina D (in Spanish; read October 2026)
- NIH Office of Dietary Supplements: Dietary Supplements, What You Need to Know (page dated January 2023)
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