SuppScoutCompare smarter. Supplement better.
Vitamin

Vitamin D

A fat-soluble vitamin sold as D2 or D3. Labels list micrograms (mcg), often with IU in parentheses.

Last reviewed September 28, 20263 sources2 forms
In short

Vitamin D is a fat-soluble vitamin that helps the body absorb calcium and maintain bone. The skin makes vitamin D when exposed to UVB sunlight, and it is found naturally in a few foods and added to others. Supplements come in two forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

U.S. labels list vitamin D in micrograms (mcg); many also show International Units (IU). The conversion is fixed: 1 mcg = 40 IU, so 25 mcg = 1,000 IU and 50 mcg = 2,000 IU.

Quick facts

Type
Fat-soluble vitamin
RDA
15 mcg (600 IU) ages 1–70; 20 mcg (800 IU) over 70[1][2]
Upper limit (age 9+)
100 mcg (4,000 IU)/day[1]
Unit conversion
1 mcg = 40 IU
Forms
D2 (ergocalciferol), D3 (cholecalciferol)

Common vitamin d supplement forms

FORM

Vitamin D3 (Cholecalciferol)

The form of vitamin D the skin makes from sunlight. Most D3 supplements are made from lanolin; vegan D3 is made from lichen.

D2 vs D3 →
FORM

Vitamin D2 (Ergocalciferol)

A plant- and fungus-derived form of vitamin D made by exposing yeast or mushrooms to UV light. It’s vegan and used in some prescriptions and…

D2 vs D3 →

What researchers have studied it for

Vitamin D supplements reliably raise vitamin D status, and D3 tends to raise blood levels more than D2 in comparative research. For outcomes beyond vitamin D status — fractures, cancer, heart disease — large trials in generally healthy adults have mostly been disappointing, while people with low status or specific medical needs are a different situation best handled with a clinician.

Correcting low vitamin D status

Consistent evidence

Both D2 and D3 supplements raise blood levels of 25-hydroxyvitamin D, the standard marker of vitamin D status.[1][3]

Bone health (with calcium)

Mixed evidence

Vitamin D is required for calcium absorption and bone health. Trials of supplements for preventing fractures and falls in generally healthy community-dwelling adults have produced mixed results; effects appear more likely in people with low vitamin D status.[1]

Cancer and cardiovascular disease

Insufficient evidence

Large randomized trials, including the VITAL trial summarized by the NIH, did not find that vitamin D supplements reduced overall rates of cancer or cardiovascular events in generally healthy adults.[1]

Evidence labels summarize the overall body of published research for each topic; they are not a recommendation and do not mean a supplement is appropriate for you. Published research

Typical amounts in supplements

Single-ingredient supplements commonly contain 25 mcg (1,000 IU) to 50 mcg (2,000 IU) per serving, with higher-dose products available. The Upper Intake Level for people 9 and older is 100 mcg (4,000 IU) per day from all sources; clinicians sometimes use higher amounts short-term for deficiency under supervision.

[1]
Common per-serving range
25–50 mcg (1,000–2,000 IU)
UL (age 9+)
100 mcg (4,000 IU)/day
RDA ages 1–70
15 mcg (600 IU)

These describe what supplements commonly contain and published reference values — not a recommendation for you.

Food sources

  • Fatty fish such as trout, salmon and sardines
  • Fortified milk and many plant milks
  • Fortified cereals and some orange juice
  • Egg yolks and beef liver (small amounts)
  • Mushrooms exposed to UV light (vitamin D2)

Source[1]

Potential considerations

  • Too much vitamin D, almost always from high-dose supplements, can cause high blood calcium with symptoms such as nausea, muscle weakness, confusion and kidney problems.
  • Because it’s fat-soluble, vitamin D can accumulate; stacking several products (a multivitamin plus a D supplement plus fortified foods) adds up.
  • D3 is commonly made from lanolin (sheep’s wool); vegan D3 is made from lichen. D2 is typically produced from yeast or fungi.

Interactions and warnings

  • Orlistat (a weight-loss drug) can reduce absorption of vitamin D.[1]
  • Statins and vitamin D may affect each other’s metabolism (studied mostly with atorvastatin).[1]
  • Steroids such as prednisone can reduce calcium absorption and impair vitamin D metabolism.[1]
  • Thiazide diuretics combined with vitamin D can raise the risk of high blood calcium, especially in older adults.[1]

Not a complete list. Ask a pharmacist or clinician about your specific medications.

Who should speak to a healthcare professional first

  • Anyone considering more than 100 mcg (4,000 IU) per day
  • People taking the medications listed above
  • Anyone with kidney disease, sarcoidosis or a history of high blood calcium
  • Anyone who is pregnant or breastfeeding

Products containing vitamin d

Primary ingredient
Vitamin D3 (Cholecalciferol)
Per serving
25 mcg (1,000 IU) vitamin D
Servings
30
Format
Gummies
Price
Not available
Per serving cost
—
Not verified
View details

Plainlabel Vitamin D2 1,000 IU

Plainlabel Nutrition · Demo
Primary ingredient
Vitamin D2 (Ergocalciferol)
Per serving
25 mcg (1,000 IU) vitamin D
Servings
120
Format
Tablets
Price
Unavailable
Per serving cost
$0.08
Not verified
View details
All 4 vitamin d products →

SuppScout may earn a commission when you purchase through certain links. This does not affect how products are compared. Learn more.

Related comparisons

VITAMIN D

D2 vs D3

Sources, vegan status and what research says about raising levels.

Compare →

Guides & research

VITAMIN D

How to Compare Vitamin D Supplements

Units, D2 vs D3, source, totals across products and cost per 1,000 IU.
LABEL BASICS

Supplement Serving Size Explained

Why “per serving” can mean one capsule or five, and how that changes comparisons.
FORMATS

Capsules vs Powders vs Gummies

How format affects amount per serving, other ingredients and cost.
LABEL BASICS

How to Read a Supplement Label

Serving size, amount per serving, ingredient form, other ingredients and testing information — in the order that matters.
EVIDENCE REVIEW

Vitamin D2 vs D3: Reading the Research

What the 2012 meta-analysis compared, and how dosing pattern changed the result.

Frequently asked questions

How many IU is 25 mcg of vitamin D?

1,000 IU. Multiply mcg by 40 to get IU, or divide IU by 40 to get mcg.

Is vitamin D3 better than D2?

Both raise vitamin D levels. A 2012 meta-analysis found D3 was more effective at raising blood 25-hydroxyvitamin D than D2, especially with large, infrequent doses. D2 is usually vegan by default, and vegan D3 from lichen is also available. See D2 vs D3.

Is vitamin D3 vegan?

Usually not — most D3 comes from lanolin, a substance from sheep’s wool. Look for D3 labeled as sourced from lichen, or choose D2.

Sources & references

  1. Vitamin D: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. ods.od.nih.govGovernment
  2. Institute of Medicine (2011). Dietary Reference Intakes for Calcium and Vitamin D. The National Academies Press. nap.nationalacademies.orgGovernment
  3. Tripkovic L, Lambert H, Hart K, et al. (2012). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition 95(6). doi:10.3945/ajcn.111.031070Meta-analysis

SuppScout links to primary and authoritative sources wherever possible. See our editorial policy for how sources are selected and how corrections are handled.

This page is educational and is not medical advice. Talk to a healthcare professional before starting a supplement, especially if you have a medical condition, take medications, or are pregnant or breastfeeding. Medical disclaimer.