Glass of Milk (IMAGE) Oregon State University Caption Milk is one of the sources of vitamin D. About 70 percent of Americans, and up to a billion people worldwide, have insufficient levels of vitamin D. Credit Photo: Theresa Hogue/OSU Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.