How Long Does It Take Vitamin D3 to Work?
Depending on how deficient you are, it could take 2 to 3 months to get your vitamin D levels where they need to be.
Even with the guidelines from the National Institutes of Health, there has yet to be an international agreement on vitamin D intake.
The Endocrine Society recommends 1,500 to 2,000 IU daily for adults, while the United Kingdom advises just 400 IU per day for those four or older (11, 12).
To determine your unique vitamin D dosage, consult your doctor. Again, the dosage can depend on your current state of health, skin pigmentation, and weather.
Is It Possible to Take Too Much Vitamin D3?
Although extremely rare, vitamin D toxicity can occur at extremely high doses. The reported doses of vitamin D toxicity actually happening range from 50,000 IU to 1,604,000 IU per day (13).
This toxicity results in a buildup of calcium in your blood (hypercalcemia), causing nausea, vomiting, weakness, and frequent urination. It may also lead to bone pain and kidney problems, like the formation of calcium stones (14, 13).