According to Harvard Men's Health Watch, recent studies have linked multivitamin use to prostate cancer. "Scientists have many unanswered questions about folic acid and cancer. One popular theory, still unproven, suggests that timing and dose may explain folate's apparently contradictory effects on cancer," researchers said. The news could strike a damaging blow to the multivitamin market if consumers stop buying multivitamins which contain folic acid. But this morning the Council for Responsible Nutrition (CRN) said there was no reason to stop taking multivitamins. CRN vice-president for regulatory and scientific affairs, Andrew Shao, said: "The issue raised on folic acid from a scientific standpoint is one that warrants follow-up, but it is not something isolated to multivitamins. "The majority of Americans don't eat well… and multivitamins are an important component to the diet." "If you have a disease or health condition and are on medications any changes you make to your diet should be discussed with your physician." Multivitamin/mineral supplements are regularly taken by over one-third of American adults, equivalent to about 73m people, and make up a substantial part of the $23bn spent by consumers every year on dietary supplements. Harvard suggested the average man could give up the multivitamin, at least until scientists solve the "puzzle of folic acid and cancer". They said: "There is no proof that a daily multi vitamin 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 possibly prostate and breast cancers."Harvard added that if men stop taking a multivitamin, they should consider taking a vitamin D supplement. This is because the typical diet for most men and women does not supply enough of this vitamin, Harvard said. Damaging Indeed, last May a study from the US National Cancer Institute reported that taking excessive amounts of multivitamins may increase the risk of advanced and fatal prostate cancers by 30 per cent. The study, published in the Journal of the National Cancer Institute, assessed the diets of 295,344 men without prostate cancer, and found that during five years of follow-up men who consumed multivitamins more than seven times a week had increased risks of advanced and fatal prostate cancers. No effect was observed for early or localized prostate cancer.