I don't think taking a vitamin is going to prevent an ED, considering its first and foremost a psychological disorder based on many factors. ED patients only use food as a source of their emotions/control, and its merely a by-product/tool/coping mechanism
If anything, the person who wrote the article should have made it clear that Anorexia Nervosa caused physical complications ie: malnutrition, osteoporosis etc may be helped by taking said vitamins/supplements.