“‘You might want to stop taking [these],’” Gulati told her father.
Often, preliminary studies fuel irrational exuberance about a promising dietary supplement, leading millions of people to buy into the trend. Many never stop. They continue even though more rigorous studies—which can take many years to complete—almost never find that vitamins prevent disease, and in some cases find that they cause harm.
“The enthusiasm does tend to outpace the evidence,” said Dr. JoAnn Manson, chief of preventive medicine at Boston’s Brigham and Women’s Hospital.
In Search of the Magic Bullet
A big part of the problem, Kramer said, could be that much nutrition research has been based on faulty assumptions, including the notion that people need more vitamins and minerals than a typical diet provides; that megadoses are always safe; and that scientists can boil down the benefits of vegetables like broccoli into a daily pill.But when researchers tried to deliver the key ingredients of a healthy diet in a capsule, Kramer said, those efforts nearly always failed.
More important, perhaps, is that most Americans get plenty of the essentials, anyway. Although the Western diet has a lot of problems—too much sodium, sugar, saturated fat, and calories, in general—it’s not short on vitamins, said Alice Lichtenstein, a professor at the Friedman School of Nutrition Science and Policy at Tufts University.
Without even realizing it, someone who eats a typical lunch or breakfast “is essentially eating a multivitamin,” said journalist Catherine Price, author of “Vitamania: How Vitamins Revolutionized the Way We Think About Food.”
That can make studying vitamins even more complicated, Price said. Researchers may have trouble finding a true control group, with no exposure to supplemental vitamins. If everyone in a study is consuming fortified food, vitamins may appear less effective.
The body naturally regulates the levels of many nutrients, such as vitamin C and many B vitamins, Kramer said, by excreting what it doesn’t need through the urine. “It’s hard to avoid getting the full range of vitamins,” he said.
Vitamin Users Start Out Healthier
For Charlsa Bentley, 67, keeping up with the latest nutrition research can be frustrating. She stopped taking calcium, for example, after studies found it doesn’t protect against bone fractures. Additional studies suggest that calcium supplements increase the risk of kidney stones and heart disease. “I faithfully chewed those calcium supplements, and then a study said they didn’t do any good at all,” said Bentley, a native of Austin, Texas. “It’s hard to know what’s effective and what’s not.”Bentley still takes five supplements a day: a multivitamin to prevent dry eyes, magnesium to prevent cramps while exercising, red yeast rice to prevent diabetes, coenzyme Q10 for overall health, and vitamin D based on her doctor’s recommendation.
Faulty Assumptions
Preliminary findings can also lead researchers to the wrong conclusions.In a series of clinical trials, folic acid pills lowered homocysteine levels but had no overall benefit for heart disease, Lichtenstein said.
Studies of fish oil also may have led researchers astray.
When studies of large populations showed that people who eat lots of seafood had fewer heart attacks, many assumed that the benefits came from the omega-3 fatty acids in fish oil, Lichtenstein said.
But it’s possible the benefits of sardines and salmon have nothing to do with fish oil, Lichtenstein said. People who have fish for dinner may be healthier due to what they don’t eat, such as meatloaf and cheeseburgers.
Too Much of a Good Thing?
Taking megadoses of vitamins and minerals, using amounts that people could never consume through food alone, could be even more problematic.“There’s something appealing about taking a natural product, even if you’re taking it in a way that is totally unnatural,” Price said.
Early studies, for example, suggested that beta carotene, a substance found in carrots, might help prevent cancer.
In the tiny amounts provided by fruits and vegetables, beta carotene and similar substances appear to protect the body from a process called oxidation, which damages healthy cells, said Dr. Edgar Miller, a professor of medicine at Johns Hopkins University School of Medicine.
“Vitamins are not inert,” said Dr. Eric Klein, a prostate cancer expert at the Cleveland Clinic who led the vitamin E study. “They are biologically active agents. We have to think of them in the same way as drugs. If you take too high a dose of them, they cause side effects.”
Gulati, the physician in Phoenix, said her early experience with recommending supplements to her father taught her to be more cautious. She said she’s waiting for the results of large studies, such as the trial of fish oil and vitamin D, to guide her advice on vitamins and supplements.
“We should be responsible physicians,” she said, “and wait for the data.”