Doctor's Best Vitamin D3 delivers 125 mcg (5,000 IU) of vitamin D3  as cholecalciferol, a nutrient that is critical to many bodily functions. Vitamin D3 is beneficial for supporting bone health, immunity, cardiovascular function, and cellular metabolism, among others. Mounting research is highlighting the ever-increasing benefits of optimal vitamin D3 status. Vitamin D3 is known to interact with over 200 different genes and thus plays a crucial regulatory role as a metabolic activator for a multitude of metabolic processes.