According to the latest American study women who take multivitamin supplements don't live longer than those who get their nutrients from food alone. In fact, they appear to have slightly higher death rates, researchers found.
Dr. Jaakko Mursu of the University of Minnesota in Minneapolis, who worked on the new study said, “There is very little evidence showing that common dietary supplements would be beneficial in prevention of major chronic diseases… Unless you are deficient, there is hardly any reason to take them.”
About half of adult Americans take dietary supplements, and the industry now boasts of annual sales as high as $20 billion. An editorial published in the Archives of Internal Medicine along with the study says some of the largely unregulated substances - such as vitamins A and E - could be harmful in high doses.
“The belief that antioxidant supplements are beneficial seems likely to have resulted from a collective error,” Dr. Goran Bjelakovic of the University of Nis in Serbia and Dr. Christian Gluud of Rigshospitalet in Copenhagen write. “Perhaps oxidative stress is one of the keys to extension of our life span.”
Mursu and his colleagues used data from nearly 39,000 older women who participated in the Iowa Women's Health Study and filled out questionnaires starting in 1986. The survey asked about use of multivitamins, vitamins A, C, D and E as well as beta-carotene, B vitamins and minerals such as calcium, copper, magnesium, selenium and zinc. During the study, supplements became increasingly popular: Between 1986 and 2004, the proportion of women who said they took one or more jumped from 63 percent to 85 percent.
Results revealed that only calcium supplements were linked to a lower risk of death over 19 years of follow-up, with 37 percent of users dying compared to 43 percent of nonusers. That link held up even after considering that women taking supplements had a healthier lifestyle than the rest.
But women taking other supplements did not live longer. 41 percent of multivitamin users died versus 40 percent of nonusers - and the gap became even wider when adjusting the numbers based on health problems like diabetes, high blood pressure and overweight in the two groups.
Mursu suggests his findings will be true for men as well, adding that dietary supplements do little good in Western countries where vitamin deficiency is not common. One possible exception is vitamin D, which one recent study suggests may help women live a little longer.
Mursu also cautioned that his study doesn't prove supplements cause harm. “I would rather conclude that there is no evidence for benefits,” he said.
The 2010 U.S. dietary guidelines recommend getting nutrients from foods, not supplements. However, women of reproductive age group are advised to get extra folic acid and those who are pregnant may want to take iron supplements if their doctor suggests it. The guidelines also urge people 50 and older to get extra vitamin B12 from fortified foods or supplements.
Duffy MacKay of the Council for Responsible Nutrition, a trade association representing manufacturers and ingredient suppliers of dietary supplements, disagreed with the researchers' conclusion that doctors should only recommend supplements to people with deficiencies. He added that in the case of iron, women on high doses may have underlying conditions that could explain their higher death rates.
Dr. Donald Hensrud, chair of preventive medicine at the Mayo Clinic, said the conflicting evidence seems overwhelming, but the new study helps to clarify the overall message. “It can be confusing for the public when something isn't entirely black and white,” Hensrud said. “But based on this new study, people should be even a little more cautious now about taking these supplements.”
“People take nutritional supplements for a variety of reasons, both related directly to a health problem or only related to a health belief that a little of something is good and a lot of something must be better. This is not always the case,” said Dr. Charles Clark, a professor of medicine at the Indiana University School of Medicine.
Connie Diekman, director of nutrition at Washington University in St. Louis, said women who want to take additional vitamins and minerals should consult with their doctors to make sure those supplements are safe and actually necessary. “Supplements should be viewed as ways to boost intake when food does not meet need,” she said.
Experts say the best way to ensure that one is getting all the nutrients is still to eat a well-balanced diet. Mursu advised, “Include as many vegetables and as much fruit as you can. There is hardly any reason to limit those, and they contain a whole lot of vitamins and minerals.”
The next step is for researchers to determine how much of any given nutrient is too much and why, Miriam Pappo, the director of the department of clinical nutrition at Montefiore Medical Center in the Bronx, N.Y. said. “Getting our nutritional needs through food is of course the ultimate goal, she says. Still, “few can say they meet the micronutrient nutritional guidelines of 5-9 servings of fruits/vegetables daily, which is why many take a multivitamin, and the American Medical Association recommends it for our fast-paced society.”