The vitamins can help reduce the risk of cancer in women aged over 45 who have started the menopause or who drink alcohol.
Researchers from the Brigham and Woman's Hospital and Harvard Medical School made the discovery when they analysed the health records of 37,920 women who were healthy and aged 45 or over.
During a 10-year follow-up period, 1,171 women developed breast cancer. The researchers were expecting to see that multi-vitamin use was a contributory cause of the cancers. But not only were they unable to find link, the researchers also found that the vitamins had a protective effect on women who enjoyed a drink.
(Source: American Journal of Epidemiology, 2008; 167: 1197-1206).