"Some minerals like iron and calcium affect women more than men." Katz-Cohern says. "Menstruating women should stick to a multivitamin that contains iron."

While supplements can benefit, the "mega-dose," taking too much of a given nutrient, can be harmful, says Bleday. The mega-dose usually consists of 10 times the RDA.

"The ones we are concerned about are the fat-soluble vitamins like Vitamin A and D that are stored in the fat cells," Bleday says. "When vitamins and minerals are taken in very large doses, they can only be considered medication."

A large buildup of fat-soluble vitamins, which are poorly excreted by the kidneys, can produce toxic effects. According to Willett, vitamin D can cause seizuers and death if taken in extreme excess, and vitamin A and cause liver problems.

The American Cancer Society additionally warns that too much vitamin A and D may cause headaches, blurred vision, injury to the nervous system, and other effects. Recent research has shown toxic levels of vitamins to be connected with both fat soluble and water soluble vitamin.

Willett admits that the debate over the right diet still rages. But he says that the ambiguities may soon be resolved, as researchers continue to investigate the effect of vitamins and minerals.

"There are going to be a few major papers published in the next several months that will help us understand vitamins and minerals," he says