If you start your day with a multivitamin, you are not alone. About half of all adults in this country take one a day. But few stop to question whether a multivitamin is really necessary. A Swedish study published online in the American Journal of Clinical Nutrition (September 22, 2010) found that multivitamins may help prevent heart attacks in women without heart disease, but that the vitamins had little effect on women with existing heart disease. Because women who take multivitamins are more likely to live a healthier lifestyle than those who dont, the authors admitted it is difficult to judge the impact of the vitamins themselves.