Now Vitamin D3 5000IU f provide this key vitamin in a highly absorbable liquid form. As more people avoid sun exposure, Vitamin D supplementation becomes even more necessary to ensure your body receives an adequate supply. Vitamin D is responsible for structuring and maintaining bone tissue and balancing calcium and phosphorus levels in the body (homeostasis). In addition, studies show that this vitamin is involved in other vital processes, such as cell reproduction, hormone secretion and the immune system.