A recent editorial authored by British and U.S. medical doctors and scientists in response to three new studies on vitamin and mineral supplementation, concludes that “supplementing the diet of well-nourished adults. . .has no clear benefit and might even be harmful.” Eliseo Guallar, et al., “Enough Is Enough: Stop Wasting Money on Vitamin and Mineral Supplements,” Annals of Internal Medicine, December 17, 2013. Representing the University of Warwick in the United Kingdom, Johns Hopkins University School of Medicine and the American College of Physicians, the group’s editorial is based on three studies—published in the same journal issue—that examine the effects of multivitamins on preventing heart attacks and cancer and improving cognitive function in men older than 65.

The first study, a meta-analysis of 27 studies covering more than 450,000 participants, found that taking multivitamins had no beneficial effect onpreventing cardiovascular disease or cancer. A second study examined 6,000 elderly men and found no improvement on cognitive decline after 12 years of taking supplements, and a third study revealed no advantage of supplements among 1,700 heart patients studied over an average of five years. “The message is simple,” write the authors. “Most supplements do not prevent chronic disease or death, their use is not justified, and they should be avoided.” The team also claims that an average western diet is sufficient to provide the vitamins the body needs. “These vitamins should not be used for chronic disease prevention. Enough is enough.” The authors also noted that specifically, antioxidant, folic acid and vitamin B supplements seem to hold no benefits, and beta carotene, vitamin E and high doses of vitamin A could potentially be harmful.

“The [vitamin and supplement] industry is based on anecdote, people saying ‘I take this, and it makes me feel better,’” said Edgar Miller, one of the editorial’s authors and a professor of medicine and epidemiology at Johns Hopkins University School of Medicine. “It’s perpetuated. But when you put it to the test, there’s no evidence of benefit in the long term. It can’t prevent mortality, stroke or heart attack.”
Critics note that the populations examined—one group included physicians with no health problems—are not reflective of the American population, which may not get ample nutrients and vitamins from their diets. “There’s always a nontrivial minority that’s actually getting a questionable level of some micronutrients. So multivitamins are a backstop against our poor diet,” said University of California Berkeley Professor Gladys Block. 
The Natural Products Association claimed that “the authors’ hypothesis is flawed in that multivitamins are not intended to cure chronic disease or prevent death solely on their own. They are designed to address nutrient deficiencies, and to aid in the general health and well-being of consumers. Multivitamins are not meant to serve as the answer to all of life’s ailments; they are, however, an important piece of the puzzle in leading a healthy lifestyle.”
Meanwhile, an unrelated study of adults in the Midwest has reportedly revealed that the use of certain dietary supplements, including coenzyme Q10, fish oil and echinacea, was associated with changes—both positive and negative—in diastolic and systolic blood pressure. 
Catherine McCarty, et al., “The use of dietary supplements and their association with blood pressure in a large Midwestern cohort,” BMC Complementary and Alternative Medicine, November 28, 2013. Noting that “these results should not be interpreted as causal, nor can the direction of the association be assumed to be correct because the temporality of the association is unknown,” the researchers wrote that “despite these limitations, these data are intriguing and suggest areas for further research, where sufficient evidence does not already exist, into potential dietary supplements that could be used to lower BP [blood pressure] or for which use should be cautioned in people with hypertension.” See Natural Products Association News Release and Huffington Post, December 16, 2013; CNN.com, December 17, 2013.