While 1,000 IU of vitamin D a day might seem like a large quantity, if the goal is achieving and maintaining vitamin D sufficiency, this dose is sub-efficacious when compared to higher potency dosages like 5,000 IU and 10,000 IU. And if your current vitamin D status is below 30 ng/ml, a low dose like 1,000 IU simply isn’t enough to get your levels above 30 ng/ml, much less in the winning range of around 50 ng/ml. (Ferira previously explained that vitamin D math here).
Research published by the Clinical Journal of the American Society of Nephrology reporting on the important research by the late vitamin D advocate and bone health expert Robert P. Heaney, M.D. demonstrates that taking 1,000 IU daily (of D3, not D2, which is less potent) will only raise 25(OH)D levels approximately 10 ng/ml. This simply isn’t enough if you’re dealing with vitamin D insufficiency or deficiency—or trying to maintain vitamin D sufficiency, for that matter.*
Indeed, a high-potency vitamin D supplement of 5,000 IU per day is ideal for most people; or doubling up may be necessary, as individuals may require more or less depending on their unique biology, body composition, and health considerations.
Realistically speaking, if you’re looking to raise your 25(OH)D levels at or above 50 ng/ml to be squarely vitamin D sufficient, anything lower than 3,000 IU of vitamin D3 daily is not likely to get you there—per the science.