The discovery of vitamins in the early 20th century was a huge ( ) in the history of nutritional science. People quickly accepted the idea that taking vitamin pills could ( ) to a healthy lifestyle. It is now becoming clear, however, that this may not always be true. ( ) , research suggests that not all the effects of vitamins are positive. Although they are ( ) very good for you, certain vitamins can be harmful in large quantities. Reports about the problems related to vitamins may ( ) from one vitamin to another, depending on the ( ) of your information. It is now generally agreed, however, that people who take large amounts of vitamins A and D should ( ) their habits. Too much of these vitamins can cause ( ) health problems. Interestingly, the amount of vitamin sales over the past decade has been ( ) and may actually be increasing. While the belief in the positive effects of vitamins happened quickly, the understanding that vitamins can be harmful still needs to ( ) .