“Help fight free radicals and support your immune system,” says Celestial Seasonings about the added vitamins A and C in its Antioxidant Green Tea. Hundreds of other products such as V8 V-Fusion fruit & vegetable juice, One A Day multivitamins, Ensure nutrition shakes also make claim to “support” immunity or immune function.
Does that make people who eat or take them less likely to get a cold or the flu or another infection? Hardly.
So why all the claims?
Blame it on the Food and Drug Administration which told supplement companies that “supports,” “maintains,” and “enhances immunity” are claims that don’t promise to help “prevent or lessen disease,” so they don’t need to be backed by strong evidence. Of course, preventing disease is exactly why someone would be attracted to a supplement that “supports your immune system.”
Here’s what scientists have found about some of the key nutrients that claim to “support” immunity.
The vitamins and selenium in One A Day multivitamins “support” immunity, says Bayer, while the antioxidant vitamins in Centrum Silver “help support the immune system,” says Pfizer.
Has Bayer or Pfizer tested its multivitamins to see if all that support keeps customers from getting sick? Nope. Perhaps that’s because the companies are familiar with the results of three good studies conducted since 2002 in Canada, the Netherlands, and Scotland on a total of roughly 2,150 middle-aged and older men and women.
Those who were given a standard daily multivitamin—one that supplied the Daily Value (DV) for most vitamins and minerals—for at least a year got sick just as often as those who were given a placebo. And in the two studies that looked, the multi takers were as likely to get just as sick, and to remain sick for just as long, as the placebo takers.
“Very promising.” That’s how the Council for Responsible Nutrition, the largest trade association of supplement makers, describes the impact of vitamin E on colds and other upper respiratory tract infections.
Really? In three good studies, people who took 15 IU to 74 IU of vitamin E as part of a multivitamin every day for an average of 15 months were no less likely to get a cold or the flu than similar people who took a placebo (The Daily Value, or DV, for vitamin E is 30 IU.)
And much larger doses don’t seem to help older people living on their own. In a study of 652 people aged 60 or older, those who got 300 IU of vitamin E every day for 15 months had no fewer infections than those who received a placebo.
However, in a study of 450 Boston-area nursing home residents (average age: 85), those who were given 200 IU a day of vitamin E for one year had 20 percent fewer colds than those who were given a placebo. While that’s only a modest benefit, “colds in older people are a more serious problem than in younger people,” notes lead author Simin Nikbin Meydani of Tufts University.
Zinc is a “flu-fighter” that “keeps your immune system in working order,” AARP told its members. But taking zinc didn’t prevent colds or other respiratory infections in five studies that gave 10 mg to 20 mg of zinc—alone or as part of a multivitamin—or a placebo to some 2,560 mostly older adults every day for seven months to two years. (The DV for zinc is 15 mg.)
In a sixth trial, though, the 24 adults at a senior center in Detroit who were given 45 mg of zinc every day for a year were 67 percent less likely to get sick than the 25 adults who got a placebo.
Why the discrepancy? “Many of the elderly were zinc deficient,” says researcher Ananda Prasad of Wayne State University in Detroit. “We gave them more zinc and had them take it between meals to increase its absorption.” But Prasad’s study has yet to be repeated.
Zinc lozenges are more likely to help. In some studies, sucking on at least 75 mg of zinc from lozenges every day at the first sign of a cold cut its duration—though not its severity—by up to two days.
“Vitamin A supplementation has helped make measles vaccines more effective for children with vitamin A deficiencies in developing countries,” says nutritional immunologist Simin Nikbin Meydani of Tufts University in Boston. “But vitamin A deficiency is not a problem for adults in the developed world.”
That might explain the results of three trials in which a total of roughly 2,150 men and women in Canada and Western Europe took a placebo or 1,333 IU to 2,000 IU of vitamin A as part of a multivitamin every day. (The DV is 5,000 IU.) Over the next 12 to 18 months, the people in both groups were equally likely to get sick. The multi in two of the studies also contained 2,000 IU to 26,000 IU of vitamin A from beta-carotene.
In a fourth trial, when researchers gave 180 elderly French nursing home residents a placebo or 10,000 IU of vitamin A as beta-carotene every day for two years, the vitamin takers got just as many respiratory or urogenital infections as the placebo takers.
Multivitamins: J. Am. Geriatr. Soc. 55: 35, 2007; BMJ 331: 324, 2005; JAMA 288: 715, 2002.
Vitamin E: J. Am. Geriatr. Soc. 55: 35, 2007; BMJ 331: 324, 2005; JAMA 288: 715, 2002; JAMA 292: 828, 2004.
Zinc: J. Am. Geriatr. Soc. 55: 35, 2007; BMJ 331: 324, 2005; JAMA 288: 715, 2002; Complement. Ther. Clin. Pract. 15:91, 2009; Arch. Intern. Med. 159: 748, 1999; Am. J. Clin. Nutr. 85: 837, 2007; Cochrane Database Syst. Rev. 6:CD001364, 2013.
Vitamin A: J. Am. Geriatr. Soc. 55: 35, 2007; BMJ 331: 324, 2005; JAMA 288: 715, 2002; Arch. Intern. Med. 159: 748, 1999.
This post was originally published in 2014 and is updated regularly.
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