Citing studies that show that the antioxidants and vitamins B6, B12 and folic acid in multivitamins not only don't prevent disease, but that folic acid may actually cause cancer, Harvard Medical School researchers argued against taking a daily multivitamin in the March issue of their Harvard Men's Health Watch newsletter.

The Council for Responsible Nutrition questioned the research the newsletter cited and called the multivitamin cautions "premature."

Stating that an estimated 35 percent of U.S. adults take multivitamins regularly, Harvard researchers presented a history of multivitamin research in their newsletter article titled, "Multivitamins and your health: A reappraisal." They began with antioxidant research, citing studies showing that antioxidant supplements not only don't protect against heart disease or cancer, but "in some cases, they may actually do more harm than good."

They next tackled research on the "three Bs": B6, B12 and folic acid, and concluded that recent randomized clinical trials show that B-vitamin supplements don't prevent heart disease. They also cited one U.S. study showing that people who took folic acid had more colorectal adenomas and more prostate cancers than those who took a placebo. However, the researchers cautioned, the study involved only people who were at high risk for colorectal cancer, and who took 1,000 mcg of folic acid, two and a half times the recommended daily allowance.

The researchers also cited a 2007 report in which scientists traced colorectal cancers diagnosed in the U.S. and Canada between 1986 and 2002. In the mid-1990s, they found an extra four to six diagnoses of colorectal cancer per 100,000 people in each country. "The researchers don't know what caused the blip," the Harvard researchers wrote, but "the scientists speculated that folic acid may have contributed to the uptick in colorectal cancers—not because of multivitamins, but because of foods."

The Harvard researchers pointed out that government-mandated folic acid fortification in U.S. grain products has reduced the incidence of spinal cord birth defects by up to 50 percent since 1996, but cited an unproven theory that when those fortified foods are coupled with a multivitamin, blood levels of folic acid can increase to amounts that may be associated with increased risk of cancer.

The newsletter concluded: "There is no proof that a daily multivitamin is harmful. Still, it now seems possible that the high levels of folic acid achieved by well-intentioned people who take a multivitamin and eat healthful foods could increase the risk of colorectal and possible prostate and breast cancers. Perhaps, then, the answer is to give up the multivitamin, at least until scientists solve the puzzle of folic acid and cancer."

Andrew Shao, Ph.D., CRN's vice president for scientific and regulatory affairs, said he was "a little bit disappointed" in the research the newsletter cited, noting that the antioxidant studies it referenced have been "heavily criticized by the scientific community." In addition, the folic acid research cited was "only one study. It may merit a follow-up, but it's only one study," he said.

He said the newsletter's recommendation to jettison multivitamins is "clearly a premature action. Even the Harvard professors I contacted about this thought it was premature, and said they still take their multivitamins."

Noting that multivitamins are vital to the vast majority of Americans "who come up short when it comes to getting the recommended daily nutrition," Shao said "changes to the recommendations [that people take] multivitamins don't make sense at this point." He also cited an October 2007 CRN study of 1,177 healthcare professionals that found that 87 percent of doctors and 86 percent of nurses take multivitamins, and about three-quarters of them said "it is a good idea for patients to take a multivitamin."