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Diet and Nutrition

Is 400 IU Vit D the same as 400 mg Vit D?



My multivitamin (Centrum) lists Vitamin D as 400 IU. Is there a way to correlate IU (International Units)with mg (milligrams)?

The reason I'm asking is because recent information recommends that someone who lives in northern latitudes should take 800 mg Vit D daily rather than 400 since there is less sunlight. I assumed that this meant that I should take an additional 400 mg to that already contained in my Centrum --- thus using IU and mg in this case as interchangeable. Is this correct?


A very good question. It is wise to be cautious when supplementing your diet with Vitamin D as it is the most potentially toxic of all vitamins. (Symptoms of vitamin D toxicity include: vomiting, diarrhea, headache, weight loss, kidney damage, and calcium deposited in soft tissue (like your heart and kidneys) resulting in death.)

To begin, know that the Recommended Dietary Allowance (RDA) for Vitamin D is only 5 micrograms (ug) if you are over 24 years old. This number is doubled (10 ug) for people who are still growing (it is needed for bone growth).

Here is the math: 40 International units (IU) of vitamin D are equivalent to 1 microgram. A microgram is equal to 1/1,000 of a milligram (mg). (Please note the difference between mg. and ug. The amounts you stated are MUCH larger than the RDA, 800 mg. of vitamin D is equal to 800,000 ug.!!!! Again, the RDA is only 5 ug.)

Some more facts about Vitamin D:

*It is also known as the "sunshine vitamin" because it is unique in that it can be made in the body with the help of sunlight.

*In the U.S. most cases of vitamin D deficiency show up in dark-skinned people who live in smoggy northern cities or who lack exposure to sunlight. It may also occur in societies where people traditionally wear concealing garments, those that are housebound, institutionalized, or who work the night shift and sleep during the day (therefore missing the sunlight).

*Most foods typically eaten are not high in vitamin D, therefore, it is added to milk and other foods to make sure a majority of us get an adequate amount. Other food sources include fish oils, cream, egg yolk, liver, and butter.

*There are 12 IU of vitamin D in every ounce of milk. Since 1 ug of vitamin D is equal to 40 IU, 200 IU will supply the RDA of 5 ug. (in other words, 2 cups of milk will give you the recommended amount of vitamin D).

*Natural exposure to sunlight should provide adequate amounts of vitamin D.

I hope that this has been helpful to you. If you are still concerned about your vitamin D intake, you may wish to discuss this with your doctor or a registered dietitian. To locate a dietitian in your area, refer to the website below.

Related Resources:

American Dietetic Association

For more information:

Go to the Diet and Nutrition health topic, where you can:

Response by:

Jane   Korsberg, MS, RD, LD Jane Korsberg, MS, RD, LD
Senior Instructor of Nutrition
School of Medicine
Case Western Reserve University