One question that has not been fully answered is how much vitamin D is needed to reach a given blood level. An organization in Canada, The Pure North S’Energy Foundation, has recently helped answer that question.
The Pure North S’Energy Foundation uses evidence-based nutritional supplements to prevent chronic diseases. It is Canada’s largest not-for-profit organization focused on primary prevention.
They studied the vitamin D levels of 17,614 healthy adult volunteers participating in a preventive health program. Participants reported vitamin D supplementation ranging from 0 to 55,000 IU per day and had serum 25(OH)D levels ranging from 4 to 157 ng/ml. None of the participants had high blood calcium.