Quick answer

Vitamin D3, or cholecalciferol, is the form your skin makes in sunlight and the form in many supplements. It raises blood levels of vitamin D more, and keeps them up longer, than D2. Its roles are vitamin D's roles: calcium absorption and normal bones, muscles and immune function. On labels, 50 mcg is 2,000 IU.¹

Key facts

Supplement D3 is usually made from lanolin in sheep's wool; a D3 made from lichen is animal free.¹
In trials comparing the two, D3's edge over D2 was clear with large, spaced-out doses and not with daily doses.²
5,000 IU of D3 is 125 mcg, above the adult upper limit of 100 mcg (4,000 IU) a day.^1,3
VITAL, the largest US trial of vitamin D, gave 2,000 IU of D3 a day.⁴

What vitamin D3 does in the body

Once absorbed, D3 follows the same path as any vitamin D: the liver and then the kidneys turn it into the active hormone. So the benefits of D3 are the benefits of vitamin D, and the large trials behind the grades below used D3.^1,4

Raises and maintains blood levels of vitamin D*^1,4

Strong evidence

In the VITAL trial, 2,000 IU a day raised average blood 25-hydroxyvitamin D from 29.8 to 41.8 ng/mL after one year among the 1,644 participants who had repeat blood tests, while levels on placebo barely changed. NIH notes that vitamin D3 raises blood levels more, and keeps them up longer, than vitamin D2.

Amount studied: 2,000 IU (50 mcg) of vitamin D3 a day

Helps the body absorb calcium and maintain normal bones*^1,5,6

Moderate evidence

This is vitamin D's best-established role and the basis of official intake recommendations. It matters most when intake and sun exposure are low. In adults who mostly had adequate levels already, extra vitamin D gave no added benefit for bones: VITAL tested 2,000 IU a day in 25,871 people for about five years and found no difference from placebo.

Amount studied: The recommended 15 to 20 mcg (600 to 800 IU) a day from all sources; VITAL tested 2,000 IU a day on top of diet

Contributes to normal muscle function*^1,5,7,8

Moderate evidence

Low vitamin D can cause muscle weakness, and 'contributes to the maintenance of normal muscle function' is a nutrient-function statement permitted in the EU. Extra vitamin D has not improved strength in trials: a pooled analysis of 54 placebo-controlled trials (8,747 people) found no benefit for muscle strength or physical performance, and a three-year trial of 2,000 IU a day in 2,157 adults aged 70 and over found no gain in physical performance. Read this as a reason not to run low, not as a strength aid.

Amount studied: The recommended daily intake; DO-HEALTH tested 2,000 IU a day for three years

Contributes to normal immune function*^1,5,9

Moderate evidence

NIH lists immune function among vitamin D's roles, and 'contributes to the normal function of the immune system' is a permitted nutrient-function statement in the EU. Whether supplements help people get through the year with fewer respiratory illnesses is unsettled: the latest pooled analysis, covering 40 trials and 61,589 people, found a small effect that was not statistically significant.

Amount studied: The recommended daily intake from food, sun and supplements

D3 and D2

Vitamin D3, or cholecalciferol, is the form the skin makes in sunlight. In supplements it is usually made from lanolin, a fat from sheep's wool, and an animal-free version made from lichen is also sold.¹

Vitamin D2, or ergocalciferol, is made by exposing yeast to ultraviolet light. It is also the form that mushrooms provide.¹

Both forms raise blood levels of vitamin D, but most evidence shows D3 raises them more and keeps them up longer. In a pooled analysis of trials comparing the two, D3's advantage was clear with large, spaced-out doses and was lost with daily doses.^1,2

In practice either form will raise your level. If you take vitamin D as a large dose once a week or less often, the pooled trials favor D3. Taken every day, the two performed about the same in those trials.^1,2

Other forms you may see

Some studies have used 25-hydroxyvitamin D3, which is three to five times as potent per microgram as vitamin D3, but no such supplements appear to be sold to consumers in the US.¹

Mushroom-based products carry vitamin D2, and the FDA has approved UV-treated mushroom powder as a food additive that supplies it. Some D3 softgels, ours included, hold the vitamin in oil; since fat in the gut helps vitamin D absorb, a meal with some fat does a similar job for tablets.¹

Reading a D3 label: 1,000, 2,000 or 5,000 IU

Common D3 amounts against the adult targets^1,3
Label amount	mcg	Against the 15 mcg most adults need	Against the 100 mcg upper limit
1,000 IU	25 mcg	167%	25%
2,000 IU	50 mcg	333%	50%
5,000 IU	125 mcg	833%	125%
10,000 IU	250 mcg	1,667%	250%

A 2,000 IU product sits at half the adult limit and matches the daily amount the largest trials tested. A 5,000 IU product passes the limit every day it is taken. High doses are not rare: about 3 in every 100 US adults take 4,000 IU or more a day.^1,3,4

Vitamin D3 with K2

Many products pair vitamin D3 with vitamin K2, and NIH notes that vitamin K is often sold combined with calcium, magnesium or vitamin D. The two vitamins do separate jobs, and the D3 evidence on this page comes from trials of D3 alone or with calcium, not with K2.^1,10,11

Cautions

Daily doses above 100 mcg (4,000 IU) are for a doctor to prescribe, usually for a limited time to correct a low level and with blood tests to follow. The upper limit counts food, drinks and every supplement together.³

Ask your pharmacist or doctor first

Warfarin and similar blood thinners work by blocking vitamin K. A sudden rise in vitamin K from food or supplements can weaken their effect and raise the chance of a blood clot, and a sudden drop can strengthen it and cause dangerous bleeding. NIH and the warfarin label advise keeping vitamin K intake about the same from day to day. NIH names warfarin and similar medicines used in Europe (phenprocoumon, acenocoumarol and tioclomarol), not blood thinners that work in other ways.^10,11,12,13

On the medicine's label

That warning applies to combination products too. A D3 and K2 supplement is a vitamin K supplement as far as warfarin is concerned, so do not start one without your doctor if you take warfarin.¹⁰

What's in ours

Our Vitamin D3 contains D3 only, as cholecalciferol, with no vitamin K. The amounts in each of our products are shown as printed on their labels.

What’s in ours

Vitamin D3: Vitamin D-3, 50 mcg (2,000 IU) per serving, from the label
Men's Multi: Vitamin D, 10 mcg per serving, from the label
Ashwagandha Complex: Vitamin D3, 20 mcg per serving, from the label
Immune Support: Vitamin D3, 40 mcg per serving, from the label

Questions people ask

What does vitamin D3 do for your body?

Your liver and kidneys turn D3 into the active vitamin D hormone, which tells your gut to take up calcium and phosphate and is needed for normal muscles and immune cells. It is the same job any vitamin D does; D3 just keeps blood levels up better than D2.¹

Is vitamin D3 vegan?

Usually not: most D3 is made from lanolin, the grease in sheep's wool. Vegan D3 made from lichen exists, and D2 is made from yeast. Our softgel is not vegetarian either, because its shell is gelatin.¹

Vitamin D3 2,000 IU or 5,000 IU: which should I take?

For most adults, 2,000 IU (50 mcg) is the larger of the two that stays within the 4,000 IU limit, and it is the dose VITAL tested. 5,000 IU (125 mcg) goes past the limit and belongs under a doctor's care, usually for a set period.^3,4

See what we make

Every product shows its whole label and what its lab report covers. The store opens soon.

See the Full Measure line Ashwagandha Complex Immune Support Men's Multi

Sources

*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.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.