daily multivitamin “for insurance.” Willett said that clinical trials underestimate supplements’ true benefits because they aren’t long enough, often lasting five to 10 years. It could take decades to notice a lower rate of cancer or heart disease in vitamin takers, 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, from 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.
Like many people who take
dietary supplements, Bentley also exercises regularly — playing tennis three to four times a week — and watches what she eats.
People who take vitamins tend to be healthier, wealthier and better educated than those who don’t, Kramer said. They are probably less likely to succumb to heart disease or cancer, whether they take supplements or not. That can skew research results, making vitamin pills seem more effective than they really are.
Preliminary findings can also lead researchers to the wrong conclusions.
For example, scientists have long observed that people with high levels of an amino acid called homocysteine are more likely to have heart attacks. Because folic acid can lower homocysteine levels, researchers once hoped that folic acid supplements would prevent heart attacks and strokes.
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.
Rigorous studies have failed to show that fish oil supplements prevent heart attacks. A clinical trial of fish oil pills and vitamin D, whose results are expected to be released within the year, may provide clearer questions about whether they prevent disease.
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.
“Eating fish is probably a good thing, but we haven’t been able to show that taking fish oil [supplements] does anything for you,” said Dr. Steven Nissen, chairman of cardiovascular medicine at the Cleveland Clinic Foundation.
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 School of Medicine.
Experts were shocked when two large, well-designed studies in the 1990s found that beta carotene pills actually increased lung cancer rates. Likewise, a clinical trial published in 2011 found that vitamin E, also an antioxidant, increased the risk of prostate cancer in men by 17 percent. Such studies reminded researchers that oxidation isn’t all bad; it helps kill bacteria and malignant cells, wiping them out before they can grow into tumors, Miller said.
“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.”
KHN’s coverage related to aging and improving care of older adults is supported in part by The John A. Hartford Foundation.