As the role of vitamin D in the immune system becomes better understood, oral supplementation for
vitamin D deficiency is increasingly common in
multiple sclerosis (MS) centers with many patients requiring high dose supplementation to reach adequate serum levels. However, given the wide variety of vitamin D3 (cholecalciferol) supplements available and limited regulation within the nutritional supplement industry, the true vitamin D3 content of over-the-counter (OTC) supplements is a concern.