Vitamin D Dose and Upper Limits: RDA, UL, mcg and IU

Vitamin D amounts are written in two units, the recommended amount is not the same as the label's Daily Value, and the upper limit counts everything you swallow, not only the supplement. This guide sets out the figures from the National Academies, the FDA and the NIH, and shows how to add up your own intake. It is general information for healthy adults, not medical advice or a dose for you. Our buying guide covers the other label checks.

Two units: mcg and IU

The FDA says the required unit for vitamin D on food and supplement labels is micrograms (mcg), and that IU may be added in parentheses. Its conversion is 1 mcg of cholecalciferol = 40 IU, which is also 0.025 mcg per IU. Quick equivalents:

• 10 mcg = 400 IU
• 15 mcg = 600 IU
• 20 mcg = 800 IU
• 25 mcg = 1,000 IU
• 50 mcg = 2,000 IU
• 100 mcg = 4,000 IU

Older bottles and many websites still use IU only, so convert before you compare two products.

Recommended amounts by age

MedlinePlus gives the recommended daily intake as follows. The amount for infants is an Adequate Intake (AI), the others are Recommended Dietary Allowances (RDAs).

• Infants 0 to 12 months: 400 IU (10 mcg), an AI.
• Children and teens 1 to 18 years: 600 IU (15 mcg).
• Adults 19 to 70: 600 IU (15 mcg).
• Adults over 70: 800 IU (20 mcg).
• Pregnancy and breastfeeding: 600 IU (15 mcg).

A summary of the National Academies' 2011 report by Ross and colleagues explains what an RDA means here. The RDAs of 600 IU for ages 1 to 70 and 800 IU for age 71 and older correspond to a blood level of at least 20 ng/mL (50 nmol/L) and meet the needs of at least 97.5% of the population. The report set them assuming minimal or no sun exposure, and the average requirement it used was 400 IU. An RDA is a figure for planning intake across a population from all sources, food included. It is not a prescription.

The Daily Value on the label

The FDA lists the Daily Value (DV) for vitamin D as 20 mcg, and the % Daily Value on a Nutrition Facts or Supplement Facts panel is the amount in a serving divided by that figure. The FDA says its Daily Values are based on the RDAs, and 20 mcg matches the highest of them, the 800 IU for adults over 70. Some examples:

• 10 mcg is 50% of the DV.
• 25 mcg (1,000 IU) is 125%, the figure in the FDA's own worked supplement example.
• 50 mcg (2,000 IU) is 250%.
• 100 mcg (4,000 IU) is 500%.

A %DV above 100 is not a warning by itself, because the DV is a labeling reference and not the upper limit. The next section gives the limit. Our guide to percent Daily Value explains the column in general.

Upper limits

A Tolerable Upper Intake Level (UL) is the National Academies' term for the highest daily intake that is unlikely to cause harm in almost everyone in a group. MedlinePlus lists the ULs for vitamin D:

• 0 to 6 months: 1,000 IU (25 mcg).
• 7 to 12 months: 1,500 IU (38 mcg).
• 1 to 3 years: 2,500 IU (63 mcg).
• 4 to 8 years: 3,000 IU (75 mcg).
• 9 years and older, including adults: 4,000 IU (100 mcg).

The NIH Office of Dietary Supplements says the limits cover all sources, food, drinks and supplements, and that a provider may still prescribe higher doses in some cases. The 2011 summary says the UL was set with a margin of safety, partly because of concerns about risks at blood levels above 50 ng/mL (125 nmol/L), and that levels above that should raise concerns among clinicians about potential adverse effects. A UL is a ceiling, not a goal. Anything above it belongs under a clinician's direction.

Adding up your sources

Most people take vitamin D from more than one place. Add them as you would a budget:

• Fortified milk or plant milk: look at the %DV on the carton and convert, at 20 mcg for 100%.
• A multivitamin: many contain vitamin D, so read its Supplement Facts panel.
• A calcium supplement with vitamin D, or a prenatal vitamin: the same.
• A separate vitamin D supplement.

An illustration, not advice: three 8-ounce cups of milk at about 100 IU each give 300 IU, and a 1,000 IU softgel adds 1,000 IU, for 1,300 IU, well under the 4,000 IU adult limit. Two such softgels and a multivitamin with 800 IU would still be under it, but the margin shrinks quickly if you stack high-strength products. Fish and other foods add more, and the limit is a ceiling, not a target.

What too much can do

MedlinePlus says vitamin D toxicity almost always occurs from using too many supplements. Too much can make the intestines absorb too much calcium, which may raise calcium in the blood and lead to calcium deposits in soft tissues such as the heart and lungs, confusion and disorientation, kidney damage and kidney stones, and nausea, vomiting, constipation, poor appetite, weakness and weight loss. The ODS consumer fact sheet says blood levels above 150 ng/mL (375 nmol/L) can cause symptoms such as nausea, vomiting, muscle weakness, confusion, excessive urination and thirst, dehydration and kidney stones. If you have any of these symptoms while taking supplements, stop and call a doctor. The FDA says that if you have a serious reaction, you should first contact or see your health care provider.

Prescribed doses and medicines

MedlinePlus says a provider may recommend higher doses for people with certain risk factors, conditions that reduce absorption or a low blood level. That decision is for the clinician and the blood work, not for a label. The ODS consumer fact sheet lists medicines that interact: orlistat can reduce how much vitamin D the body absorbs, statins might not work as well with high-dose vitamin D, steroids such as prednisone can lower blood levels, and thiazide diuretics could raise blood calcium too high. The FDA advises bringing a list of every supplement and medicine, with doses, to your provider.

Shopping by label amount

If a clinician has suggested a particular amount, these searches match common label amounts, and they are not recommendations: vitamin D3 400 IU (10 mcg) on Amazon (opens in a new tab), vitamin D3 1,000 IU (25 mcg) on Amazon (opens in a new tab) and vitamin D3 2,000 IU (50 mcg) on Amazon (opens in a new tab). Search results are decided by Amazon, so read the Supplement Facts panel of anything you consider, check the serving size, and confirm the amount per serving, not per bottle.

The label is the authority on your product's dose and warnings. If you are pregnant, buying for a child, have kidney disease or take medicines, ask your doctor or pharmacist before you start.