From the Research
To convert vitamin D3 1000 IU to an equivalent vitamin D2 dose, you would use the same dosage of 1000 IU, as vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are considered bioequivalent at this dosage level. For standard supplementation purposes, 1000 IU of vitamin D3 equals 1000 IU of vitamin D2. Both forms help increase serum 25-hydroxyvitamin D levels, though some research suggests vitamin D3 may be more effective at maintaining these levels over time, particularly at higher doses or with long-term use 1. When switching between these forms, it's essential to know that while they have the same IU measurement, vitamin D3 is the form naturally produced in human skin upon sun exposure and may have slightly better bioavailability. For most adults taking standard supplemental doses, either form will help address vitamin D deficiency, though vitamin D3 is generally preferred when available. If you're switching from D3 to D2 due to dietary preferences (D2 is plant-derived while D3 is typically animal-derived), the 1:1 conversion is appropriate for typical supplementation needs.
Some key points to consider:
- The European Society of Clinical and Economical Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO) recommends 1000 IU daily for patients at increased risk of vitamin D deficiency 1.
- Higher dosages of vitamin D may be required to achieve a relevant increase in 25-hydroxyvitamin D levels and normalization of parathyroid hormone (PTH) 2.
- A predictive equation can be used to guide vitamin D replacement dose in patients, taking into account factors such as starting serum concentration of 25-hydroxyvitamin D, body mass index (BMI), age, and serum albumin concentration 3.
- The recommended daily allowance for vitamin D is often inadequate for correcting low serum concentrations of 25-hydroxyvitamin D in many adult patients, and about 5000 IU vitamin D3/day may be needed to correct deficiency 3.
However, for the specific question of converting vitamin D3 1000 IU to an equivalent vitamin D2 dose, the most recent and highest quality study suggests that a 1:1 conversion is appropriate 1.