What is Doctor’s Best Vitamin D3? Doctor’s Best Vitamin D3 supports healthy bone density and structure as it is required for optimal calcium absorption. More than that, this nutrient enhances and regulates immune function, supports optimal cardiovascular function and enhances cellular function. It is made of D3, the naturally-occurring form of vitamin D. Research shows that supplemental vitamin D3 (cholecalciferol) is significantly more efficient at converting to active vitamin D in the body than vitamin D2 (ergocalciferol). This makes vitamin D3 the preferred supplemental form of this nutrient. Vitamin D deficiency is prevalent with more than 75% of Americans deficient in this nutrient. People who live in the northern half of the United States are at a greater risk of being Vitamin D deficient due to a lack of sunlight.* How does it work? Vitamin D from dietary intake or sun exposure requires two activation steps in the body. The first activation occurs in the liver, while the second activation occurs in the kidneys, allowing for regulation of calcium metabolism. Vitamin D receptors are present throughout the body, in tissue such as the skin, cartilage, heart, prostate, bones and intestines so the second activation step also takes place in local tissues. Vitamin D plays a role in most organs and systems of the body. It is hormone-like, known to interact with over 200 different genes, and plays a crucial regulatory role as a metabolic activator for a multitude of metabolic processes. It acts as a “molecular switch” by influencing the expression of multiple genes. Therefore activated vitamin D not only influences bone health, but is involved in supporting the function of the immune system, respiratory system and the musculoskeletal system.