As with all consumer products there are sure to be issues that need to resolved. Dr. Davis who writes the Heart Scan Blog has warned us before that all vitamin D is not created equal. That is some of the vitamin D will not give you the expected result of serum 25(OH)D.
His earlier warnings was that dry vitamin D in tablet form was not as potent as vitamin D in capsules. This time he has found through five of his patients that Vitamin D of the Nature Made brand has not given the expected serum 25(OH)D. Here is the article: Is it or isn’t it Vitamin D
The importance of this warning is that TESTING IS EXTREMELY IMPORTANT to assure that you have an adequate amount of vitamin D in your body.