The research, conducted as part of the Women's Health Initiative Clinical Trials and the Women's Health Initiative Observational Study, involved 161,808 post-menopausal women ages 50-79. Of that group, 41.5 percent used multivitamins over 15 study years.
The study, published in the Archives of Internal Medicine, found no overall association between multivitamin use and breast, colorectal, endometrial, kidney, bladder, stomach, ovary or lung cancer. Researchers also found no association between multivitamin use and cardiovascular disease and death.
Study leader Marian L. Neuhouser of the Fred Hutchinson Cancer Research Center in Seattle, in conjunction with Sylvia Wassertheil-Smoller of Albert Einstein College of Medicine of Yeshiva University, collected data for the multivitamin study during participants' clinic visits.
Clinic staff found 35 percent took multivitamins with minerals, 3.5 percent took multivitamins alone and 2.3 percent stress multivitamins.
"Based on our results, if you fall into the category of the women described here, and you do in fact have an adequate diet, there really is no reason to take a multivitamin," Wassertheil-Smoller said in a statement.