A decade ago, antioxidants -- nutrients such as beta carotene and vitamins C and E -- were taking the nutrition world by storm. These free-radical fighters, medical experts predicted, would extend human life by protecting us from environmental hazards, cancer and heart disease.
Antioxidants began making headlines in the early 1990s, when several large medical studies showed lower rates of cancer in people who took vitamin E and beta carotene. Seemingly overnight, antioxidants were hailed by scientists and the media as an important medical breakthrough. Vitamin E, proclaimed a Time magazine article, was a "potent lung saver." A story in U.S. News & World Report heralded beta carotene as a "miracle vitamin."
For The Record
Los Angeles Times Friday October 31, 2003 Home Edition Main News Part A Page 2 National Desk 2 inches; 59 words Type of Material: Correction
Antioxidants -- An article in Monday's Health section misstated the comments of Dr. Mark Penn of the Cleveland Clinic in Ohio about clinical research into antioxidant supplements. The story incorrectly said that Penn called primary prevention studies examining antioxidant use in healthy people a flawed research method. In fact, Penn was talking about secondary prevention studies involving unhealthy people.
For The Record
Los Angeles Times Monday November 03, 2003 Home Edition Health Part F Page 8 Features Desk 1 inches; 60 words Type of Material: Correction
Antioxidants -- A story in last Monday's Health section misstated the comments of Dr. Mark Penn of the Cleveland Clinic in Ohio about clinical research into antioxidant supplements. The story incorrectly said that Penn called primary prevention studies examining antioxidant use in healthy people a flawed research method. In fact, Penn was talking about secondary prevention studies involving unhealthy people.
The problem was, much of the research on which these claims were based was preliminary -- the result of test tube or animal experiments that didn't always pan out when scientists tried to replicate them in humans. And it wasn't long before those breathless proclamations became more measured.
The reason: In recent years, several larger research studies have found that people who took antioxidant supplements received no greater protection from chronic diseases than those who didn't. The scientific community remains split on the potential for antioxidant supplements. But one thing is clear: They no longer are considered the miracle cure they once were.
That message, however, appears not to have been fully digested by the public. About one-third of Americans take antioxidants, according to national statistics, and sales of these supplements are rising. Food companies continue to cash in on the antioxidant craze with an array of products, from pomegranate juice to blueberry tea to supplement-spiked fruit smoothies.
Experts say the scientific community must bear part of the blame for raising -- and then dampening -- the public's hopes about the health benefits of antioxidants.
"The medical community has given the public mixed signals on antioxidants and vitamins," said Dr. Marc Penn, a cardiologist at the Cleveland Clinic in Ohio who led a recent review of antioxidant research published in the British medical journal Lancet. He found that even his patients seemed to put too much faith in antioxidants. "They felt like, 'I'm on vitamin E, I'm going to be OK,' " he said.
Where did the science go wrong? An oversimplified interpretation of the science that led to misguided dietary advice is one explanation, said Marion Nestle, a professor and chairwoman of New York University's department of nutrition and food studies. "Researchers said, 'We know fruits and vegetables are good, so something in them must be good. It must be the antioxidants,' " Nestle said. The scrutiny that followed involved numerous studies that looked at antioxidants in isolation -- first in animals, then in humans -- but provided results that were inconsistent at best.
In the lab, antioxidants, including vitamin E and beta carotene, neutralized some of the potentially hazardous byproducts of cell metabolism. As cells convert food to energy, they generate charged molecules known as free radicals, which become neutralized by binding to other charged molecules. Many scientists believe that when free radicals bind to cellular structures such as DNA, it causes damage that can lead to cancer, some chronic diseases and symptoms of advancing age. Round up the free radicals with antioxidants, the theory went, and disease risks would decline.
Lab and animal studies are quick and easy to do, but they don't offer real proof of what a drug or vitamin may do for a human. Evidence from human studies took much longer to produce.
When research from large-scale human trials began to emerge in the mid-1990s, the results were mixed. Observational studies, in which researchers compared people who took antioxidants or consumed them in their diets with people who didn't, found lower rates of heart disease and cancer among antioxidant takers. But some researchers said these studies were flawed because of the so-called healthy-user effect. That is, people with lots of antioxidants in their diets may be healthier to begin with, because they may eat low-fat foods or exercise regularly.
"There are loads of studies that show that people taking supplements feel better," Nestle said. "People taking them are also healthier; they have healthier lifestyles."
To help resolve the healthy-user question, researchers designed studies in which people of varied health were randomly assigned to take antioxidants. But for every clinical trial that showed some benefit from taking antioxidants, such as lowered cancer rates or decreased risk of heart attack, another found no benefits.