Your Question, Expert Answer on Vitamin D: What is Ergocalciferol?

Q. My husband found out his vitamin D level was 16. His doctor prescribed 50,000 of ergocalciferol. What is ergocalciferol?

A. The only prescription vitamin D in the US is “ergocalciferol” at the dose of 50,000 IU (International Units). Ergocalciferol is vitamin D2, which comes from plant sources. It is made by ultraviolet irradiation of ergosterol, which is a compound from yeast.

Treatment with Ergocalciferol

A typical course of treatment is to take 50,000 IU once a week for 8 to 12 weeks. With your husband’s level starting at 16, it would be expected that this short course of higher dose vitamin D will raise his level to over 30 ng/ml. Although there is controversy over the target baseline level of vitamin D, most health care providers continue to use 30 ng/ml as the lower limit of normal.

After your husband’s vitamin D level is over 30 ng/ml with the 50,000 IU once a week prescription, a maintenance dose will be recommended to continue usually a lower dose on a daily or weekly basis. However some experts like Dr. Micheal Holick advocate continuing 50,000 IU of ergocalciferol – vitamin D2 taking one capsule every other week for maintenance of adequate vitamin D levels.

Cholecalciferol versus Ergocalciferol

When you read labels on your multivitamins, calcium plus D supplements, or vitamin D supplements alone, you may see cholecalciferol on the ingredient list. Cholecalciferol is vitamin D3, which is the vitamin D that our bodies naturally produce. It is produced from ultraviolet irradiation of the sun activating the precursor of vitamin D (7-dehydrocholesterol) in the skin to start the cascade of making active vitamin D3. For supplements, it is obtained from the lanolin of sheep’s wool.

Conventional teaching says that ergocalciferol – vitamin D2 is not absorbed as well as cholecalciferol – vitamin D3. So it takes approximately one-third more vitamin D2 to create the same increases in vitamin D levels that you would get from vitamin D3. However, a few recent publications have shown that a 1,000 IU dose of vitamin D2 daily is as effective as a 1,000 IU dose of vitamin D3 in maintaining vitamin D levels. So whether you take a daily product with vitamin D2 or D3 may not matter, it is your overall vitamin D level that is important,
not the amount you are taking.

Diane L. Schneider, MD, MSc
Author, The Complete Book of Bone Health
Medical Editor,