One hundred years after Vitamin D discovery: Is there clinical evidence for supplementation doses?

In the last decade, an increasing awareness was directed to the role of Vitamin D in nonskeletal and preventive roles for chronic diseases in different fields. Vitamin D deficiency was reported in many countries worldwide and is considered as a pandemic. However, no consensus exists about whether and how supplementation of Vitamin D may be beneficial as a preventive or adjuvant therapy. Thereby, this review aimed to deliver an overview about the administrated doses of Vitamin D in randomized controlled clinical studies, in order to evaluate the currently available clinical evidence. In addition, focus was placed on the recent advances on Vitamin D nonskeletal actions. The results sometimes showed a great discrepancy between the recommended Vitamin D dose by different guideline authorities, which are from 400 to 4000 IU/day, and the used doses in recent randomized controlled clinical studies, which were up to 100,000 IU/day. Different studies showed the positive effect of Vitamin D in supporting the immune system and preventing different chronic and infectious diseases. These findings reflect the need to rethink existing reference ranges and intake recommendations. Based on the analyzed range of clinically applied doses, we recommend a Vitamin D supplementation based on three different ranges, which include 40 80 ng/ml with oral Vitamin D intake of 10,000 IU/day, 5000 IU/day, and 1000 IU/day, respectively. A 25-hydroxyvitamin D blood serum monitoring is furthermore recommenced every 3 months to re-adjust the Vitamin D dose based on the above-mentioned concept. Ongoing clinical studies will have to further prove this concept for different patient groups.