Dr.s are uneducated when it comes to vitamins because they only get about 40 minutes total on vitamins in medical school. Less if they went to med school pre 1996. Vitamins often need other vitamins to work. If you are taking Vitamin D3 it is absolutely necessary to take Vitamin K. It is much like how you need Vitamin C to utilize iron supplements. Calcium D3 and Vitamin K all need each other for your body to use it properly, unless it is D3 from the sun.