Guide
What is vitamin D? A plain guide
Vitamin D3 is a form of vitamin D, not a different vitamin. A plain guide to the forms, the label numbers and what the large trials at 2,000 IU found.
Vitamin D is a fat-soluble vitamin that your skin makes in sunlight and that you also get from some foods and supplements. Vitamin D3 (cholecalciferol) is one of its two supplement forms, the other being D2 (ergocalciferol). So vitamin D3 is not a different vitamin from vitamin D: it is a kind of vitamin D.
Is vitamin D3 the same as vitamin D?
"Vitamin D" is the family name. Two forms are sold as supplements:
- Vitamin D3, cholecalciferol. The form your skin makes when it is exposed to ultraviolet light. Supplement D3 is usually sourced from animals (lanolin from sheep's wool is common); fatty fish and egg yolk contain it too.
- Vitamin D2, ergocalciferol. The form made by plants and fungi, used in some fortified foods and supplements.
When a label says "vitamin D" without a letter, read the ingredient line: it names the form. Our guide to choosing a vitamin D goes through what else to check.
What is the difference between vitamin D and vitamin D3?
The difference that has been measured is in blood levels. A 2012 systematic review and meta-analysis of randomised trials that compared D2 directly with D3 found D3 raised blood 25-hydroxyvitamin D (the marker clinicians test) more than D2 overall. The advantage was clear for single large doses but was lost when the vitamin was taken daily. That is a blood-marker result, not a health outcome, and it does not tell you that either form does more for you.
What does vitamin D do in the body?
According to the National Institutes of Health Office of Dietary Supplements (NIH ODS), vitamin D helps the body absorb calcium and phosphorus from food, and it is needed for normal bone. Muscle, nerve and immune cells also use it. Those are statements about what the nutrient does in the body. They are not claims about what a supplement will change for you, and the next section is why we keep the two apart.
What vitamin D3 supplements have and haven't been shown to do
The largest trials of vitamin D3 at 2,000 IU a day (VITAL, about 25,000 generally healthy US adults aged 50 and over, followed a median 5.3 years) found no difference from placebo in cancer or major cardiovascular events, in fractures, or in depression. Those were adults not selected for low vitamin D, so the results say little about people who are low. We have set out the full picture, including the findings that were positive, in vitamin D benefits: what the research does and doesn't show.
How do you know if your level is low?
Not by symptoms. Low vitamin D often produces nothing you would notice, and the symptoms people list overlap with many other things. NIH ODS describes status as measured by a blood test of 25-hydroxyvitamin D, which a clinician interprets. If you are wondering about your level, that test is the answer, and the result tells you more than a guess about a supplement does.
Vitamin D3 labels: mcg, IU and the numbers on the bottle
Labels print vitamin D in micrograms (mcg), international units (IU), or both. The conversion is 1 mcg = 40 IU, so:
| Label says | In mcg | Against the adult upper limit (100 mcg) |
|---|---|---|
| 1,000 IU | 25 mcg | 25% |
| 2,000 IU | 50 mcg | 50% |
| 5,000 IU | 125 mcg | 125%, above it |
| 10,000 IU | 250 mcg | 250%, above it |
| 50,000 IU | 1,250 mcg | 1,250%, above it |
The upper limit and the other reference numbers are explained in how much vitamin D should you take a day. Watch the unit: mg, mcg and IU are not interchangeable, and a label or search for "vitamin D3 50 mg" is a unit mix-up, since 1 mg is 1,000 mcg, or 40,000 IU.
What is in our Vitamin D3 softgel
Electric Tiger Vitamin D3 has 50 mcg (2,000 IU) of vitamin D3 as cholecalciferol per softgel, which is 250% of the Daily Value (a labeling reference of 20 mcg, not a limit). The adult upper limit is 100 mcg (4,000 IU) a day from all sources, so one softgel is half of it. There are 100 softgels a bottle, as low as $15.35 a bottle on subscription. We make no claim that taking it changes any health outcome, for the reasons above.
Questions people ask
What is vitamin D3?
The form of vitamin D called cholecalciferol: the one your skin makes in sunlight, and a common supplement form. See the first section for how it differs from D2.
What is vitamin D3 for?
In the body, vitamin D helps absorb calcium and phosphorus and is needed for normal bone (NIH ODS). What a supplement does beyond that depends on who takes it and how much: see the benefits review linked above, which reports trial results at 2,000 IU.
When do I take vitamin D3, and how?
Our label directs one softgel daily, or as directed by a health care professional. Taking it with a meal that contains fat is the one timing point with trial support: see when is the best time to take vitamin D.
What about vitamin D3 and K2?
Vitamin K2 is a separate vitamin, and we sell no K2 product. We make no claim about the pair; the question is covered on its own in magnesium glycinate with vitamin D3 and K2.
Is vitamin D3 for men and women different?
The reference numbers in this guide (RDA, upper limit) are the same for adult men and women. We give no separate guidance by sex.
Sources
- Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis D3 raised blood vitamin D levels more than D2 overall, but the difference disappeared when it was taken daily.
- Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease In 25,871 older adults, 2,000 IU a day for a median 5.3 years did not lower cancer or heart-event rates versus placebo.
- Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults In 25,871 healthy older adults, 2,000 IU a day for about 5 years did not change the fracture rate versus placebo.
- Effect of Long-term Vitamin D3 Supplementation vs Placebo on Risk of Depression or Clinically Relevant Depressive Symptoms and on Change in Mood Scores: A Randomized Clinical Trial In 18,353 older adults, 2,000 IU a day for about 5 years changed neither depression risk nor mood scores versus placebo.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
