Vitamin D3, also called cholecalciferol, forms naturally when you expose your skin to the sun and also appears in supplements. Its chemical structure differs slightly from that of another form of the vitamin, called D2, or ergocalficerol. However, both forms of the vitamin have highly similar effects inside your body, and the only real difference between 400 IU of vitamin D and 1,000 IU of vitamin D3 is the amount of the vitamin you consume.
Different Vitamin Forms
Vitamin D2 is a plant-based substance. Supplemental forms of the vitamin come from the irradiation of a yeast component called ergosterol. Supplemental forms of vitamin D3 come from either chemical alteration of animal cholesterol or from the irradiation of a specific form of cholesterol derived from the sebaceous glands of wool-bearing animals. Despite minor differences in their chemical structures, both D2 and D3 are processed by your body in more or less identical ways. When taken at levels that support your general health, they produce the same body effects.
Understanding International Units
IU is an abbreviation for the term "international unit." The designation of IU in the dosage of a drug or vitamin indicates an international scientific agreement on the effects of that dosage. The specific amount contained in an IU varies with the medication or vitamin in question. A single IU of vitamin D contains 0.000025 mg of the vitamin. Therefore, 400 IU of the vitamin equals 0.01 mg, while 1,000 IU equals 0.025 mg.
Recommended Intakes
Infants need at least 400 IU of vitamin D per day, according to the National Academy of Sciences' Institute of Medicine, which sets nutrient intake standards for the U.S. All other children and adults up to age 70 need at least 400 IU, but require 600 IU for optimal health. Adults over 70 need at least 400 IU, but require 800 IU for optimal health. Until they reach six months, infants have a maximum safe daily vitamin D intake of 1,000 IU. Maximum safe intakes for other age groups range from 1,500 to 4,000 IU. Intake totals include both food and supplemental sources of the vitamin.
Considerations
Although common intakes of D2 and D3 have the same effects on your body, high doses of D2 are less potent than high doses of D3, the Office of Dietary Supplements notes. Your doctor might recommend high vitamin D dosages for the treatment of specific health problems, including vitamin deficiency. Because you can get vitamin D from sunlight in addition to food sources, doctors can have difficulty fully assessing your vitamin D status. For this reason, the Institute of Medicine's recommendations assumes you have minimal sunlight exposure. Consult your doctor for more information on appropriate amounts of vitamin D for your particular circumstances.
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