Doctor's Best Vitamin D3 is a "sunshine vitamin" that helps support immune, heart, and bone health.* Vitamin D3 enhances and regulates immune function, supports optimal cardiovascular function and enhances cellular function.* Vitamin D3 (cholecalciferol) is a nutrient that is critical to many bodily functions. Vitamin D3 is beneficial for supporting bone health, immune wellness, cardiovascular function, and cellular metabolism, among others. Mounting research is highlighting the ever-increasing benefits of optimal vitamin D3 status.