The most recent study (published in the The Archives of Internal Medicine) on multivitamins continue to show that there are no special health benefits.  This eight-year study that included 161,808 post-menopausal women found the pills did nothing to prevent common cancers or heart disease. [Multivitamins May Not Cut Cancer Odds (WebMD)]

A previous study done by the National Cancer Institute already had bad news for the industry when it reported that Men who take multi-vitamin supplements more than once a day are twice as likely to die of prostate cancer as men who never take supplements, researchers confirmed. [Mega Multivitamin Use Risks Prostate Cancer (MedPage Today)]

An eight-year study completed in November, 2008 and published in The Journal of the American Medical Association also showed no benefits from vitamin C & E supplements in preventing heart attacks or strokes.  This was a large disappointment since there had been much excitement surrounding antioxidants like vitamin C, vitamin E, and beta-carotene as a way to help protect against cardiovascular disease by slowing the formation of plaque in the arteries. [Vitamins C and E Don't Cut Heart Risks (WebMD)]

There has always been evidence suggesting vitamin supplements aren't effective because of their low bioavailability. But this only applies to most of the water soluble vitamins, like C and B vitamins.  It is possible to overdose on some fat soluble vitamins like A and K.

Will this finally put a dent in the 20-billion-dollar per year supplement industry?