MEDICINE The Myth  of Antioxidants The hallowed notion that oxidative damage causes aging and that vitamins might preserve our youth is now in doubt By Melinda Wenner Moyer

62 Scientific American, February 2013 © 2013 Scientific American © 2013 Scientific American Melinda Wenner Moyer is a science writer and frequent contributor based in Brooklyn, N.Y. She is also an adjunct assistant professor at the City University of New York Graduate School of Journalism.

avid Gems’s life was turned upside down in 2006 by a group of worms that kept on living when they were supposed to die. As assistant director of the Institute of Healthy Aging at University College London, Gems regu- larly runs experiments on Caenorhabditis elegans, a roundworm that is often used to study the biology of aging. In this case, he was testing the idea that a buildup of cellular damage caused by oxidation—technically, the chemical removal of electrons from a molecule by highly reactive compounds, such as free radicals—is the main mechanism behind aging. According to this the- ory, rampant oxidation mangles more and more lipids, proteins, snippets of DNA and other Dkey components of cells over time, eventually compromising tissues and organs and thus the functioning of the body as a whole.

Gems genetically engineered the not produce these particular antioxidants; longer than the mice missing their antiox- round­worms so they no longer produced they accumulated free radicals as predict- idant enzymes. Yet “I watched those god- certain enzymes that act as naturally oc- ed, and yet they did not die young—despite damn life span curves, and there was not curring antioxidants by deactivating free suffering extreme oxidative damage. an inch of difference between them,” radicals. Sure enough, in the absence of Other scientists were finding similarly Richardson says. He published his in- the antioxidants, levels of free radicals in confounding results in different lab ani- creasingly bewildering results in a series the worms skyrocketed and triggered po- mals. In the U.S., Arlan Richardson, direc- of papers between 2001 and 2009. tentially damaging oxidative reactions tor of the Barshop Institute for Longevity Meanwhile, a few doors down the hall throughout the worms’ bodies. and Aging Studies at the University of from Richardson, physiologist Rochelle Contrary to Gems’s expectations, how- Texas Health Science Center in San Anto- Buffenstein has spent the past 11 years ever, the mutant worms did not die prema- nio, genetically engineered 18 different trying to understand why the longest-liv- turely. Instead they lived just as long as strains of mice, some of which produced ing rodent, the naked mole rat, is able to normal worms did. The researcher was more of certain antioxidant enzymes than survive up to 25 to 30 years—around mystified. “I said, ‘Come on, this can’t be normal and some of which produced few- eight times longer than a similarly sized right,’ ” he recalls. “ ‘Obviously something’s er of them than normal. If the damage mouse. Buffenstein’s experiments have gone wrong here.’ ” He asked another in- caused by free radical production and shown that naked mole rats possess low- vestigator in his laboratory to check the re- subsequent oxidation was responsible for er levels of natural antioxidants than sults and do the experiment again. Noth- aging, then the mice with extra antioxi- mice and accumulate more oxidative ing changed. The experimental worms did dants in their bodies should have lived damage to their tissues at an earlier age Corbis

IN BRIEF

For decades researchers assumed that highly reac- Recent experiments, however, show that increases If these results are confirmed, they may suggest that tive molecules called free radicals caused aging by in certain free radicals in mice and worms correlate taking antioxidants in the form of vitamins or other damaging cells and thus undermining the function- with longer life span. Indeed, in some circumstances, supplements can do more harm than good in other- ing of tissues and organs. free radicals seem to signal cellular repair networks. wise healthy individuals. PRECEDING PAGES: THOMAS BORN PRECEDING PAGES:

64 Scientific American, February 2013 © 2013 Scientific American than other rodents. Yet paradoxically, EVIDENCE FROM HUMANS they live virtually disease-free until they die at a very old age. To proponents of the long-standing ox- When Vitamins Kill idative damage theory of aging, these Epidemiological studies show that people who eat lots of fruits and vegetables, which findings are nothing short of heretical. are rich in vitamins and other antioxidants, tend to live longer and are less likely They are, however, becoming less the ex- to develop cancer compared with those who do not. So it seemed obvious that ception and more the rule. Over the course supplementing diet with antioxidants should lead to better health. But the results of of the past decade, many experiments de- the most rigorously designed studies do not support that assumption. Indeed, the signed to further support the idea that evidence shows that some people who take certain supplements are actually more free radicals and other reactive molecules likely to develop life-threatening illnesses, such as lung cancer and heart disease. drive aging have instead directly chal- lenged it. What is more, it seems that in Early Signs That Antioxidants Can Spell Trouble certain amounts and situations, these A 1996 study of some 18,000 men and women found 28 percent more lung cancers and 17 percent more high-energy molecules may not be dan- deaths in a group that was given beta-carotene and retinol compared with people who did not receive gerous but useful and healthy, igniting in- the antioxidants. The increased risk became clear after 18 months, particularly in heavy smokers, and was trinsic defense mechanisms that keep our strongest among smokers who had been exposed to asbestos, a known carcinogen. bodies in tip-top shape. These ideas not Heavy Smokers Smokers Exposed to Asbestos only have drastic implications for future antiaging interventions, but they also 3 3 raise questions about the common wis- dom of popping high doses of antioxidant Antioxidants Antioxidants 2 2 vitamins. If the oxidative-damage theory is wrong, then aging is even more compli- 1 1 cated than researchers thought—and they Placebo Placebo may ultimately need to revise their under- standing of what healthy aging looks like 0 0 0 1 2 3 4 5 0 1 2 3 4 5

on the molecular level. Lung Cancer (percent) of Incidence Incidence of Lung Cancer (percent) of Incidence “The field of aging has been gliding Years after Study Started Years after Study Started

along on this set of paradigms, ideas

) about what aging is, that to some extent Bottom Line: Taking Some Vitamins Can Shorten Life Span were kind of plucked out of the air,” Gems

bottom In 2007 researchers reviewed 68 of the most scientifically rigorous studies of vitamins and reported that says. “We should probably be looking at pooling the data from the 47 trials with the least scientific bias resulted in a 5 percent increase in the rate other theories as well and considering, of early death. Further analysis linked the increased risk to beta-carotene, vitamin A and vitamin E. fundamentally, that we might have to look Lower rate of mortality Higher rate of mortality completely differently at biology.” for antioxidant users for antioxidant users

VOL. 297, NO. 8; FEBRUARY 28 ( 28 FEBRUARY 8; NO. 297, VOL. THE BIRTH OF Bars = 95% confidence interval JAMA, A RADICAL THEORY The oxidative damage, or free radical, the- ory of aging can be traced back to Den­ Each dot represents one trial ham Harman, who found his true calling in December 1945, thanks to the Ladies’

); “MORTALITY IN RANDOMIZED TRIALS OF ANTIOXIDANT SUPPLEMENTS FOR FOR SUPPLEMENTS ANTIOXIDANT OF TRIALS IN RANDOMIZED “MORTALITY ); Home Journal. His wife, Helen, brought a top copy of the magazine home and pointed out an article on the potential causes of aging, which he read. It fascinated him. Back then, the 29-year-old chemist was working at Shell Development, the research arm of Shell Oil, and he did not VOL. 88, NO. 21; NOVEMBER 6, 1996 ( 1996 6, NOVEMBER 21; NO. 88, VOL. have much time to ponder the issue. Yet nine years later, after graduating from medical school and completing his train- ing, he took a job as a research associate Overall at the University of California, Berkeley, and began contemplating the science of 0.01 0.1 1.0 10 100 Equal risk aging more seriously. One morning while Lowest risk (10-fold risk) Highest risk sitting in his office, he had an epiphany— Relative Risk of Dying Early for Groups That Received Antioxidant Treatment JOURNAL OF THE NATIONAL CANCER INSTITUTE, CANCER INSTITUTE, THE NATIONAL OF JOURNAL

SOURCE: “RISK FACTORS FOR LUNG CANCER AND FOR INTERVENTION EFFECTS IN CARET, THE BETA-CAROTENE AND RETINOL EFFICACY TRIAL,” BY GILBERT S. OMENN ET AL., AL., OMENN ET S. GILBERT BY TRIAL,” EFFICACY AND RETINOL THE BETA-CAROTENE IN CARET, EFFECTS INTERVENTION AND FOR CANCER LUNG FOR FACTORS “RISK SOURCE: IN IN AL., ET GORAN BJELAKOVIC BY AND META-ANALYSIS,” REVIEW SYSTEMATIC PREVENTION: AND SECONDARY PRIMARY “you know just ‘out the blue,’ ” he recalled

February 2013, ScientificAmerican.com 65 © 2012 Scientific American © 2012 Scientific American EVIDENCE FROM ANIMALS dants that they had been fed, and thus the overall level of free radicals in their blood Insight from Mutant Worms had not changed. By the 1990s, however, genetic advances allowed scientists to test Rather than causing aging (through oxidative chemical reactions that trigger cellular the effects of antioxidants in a more pre- damage), some free radicals may prove beneficial. One possibility, supported by the cise way—by directly manipulating ge- work of Siegfried Hekimi and Wen Yang, is that a certain number of free radicals nomes to change the amount of antioxi- stimulate an organism’s internal repair mechanisms to get to work. In their experiment dant enzymes animals were capable of on roundworms, published in 2010, the researchers genetically modified a group of producing. Time and again, Richardson’s worms so that they produced high levels of certain free radicals. Much to their surprise, experiments with genetically modified the mutant worms lived longer than the normal worms. When the investigators fed mice showed that the levels of free radical antioxidants to the mutant worms, their longevity advantage disappeared. molecules circulating in the animals’ bod- ies—and subsequently the amount of oxi- dative damage they endured—had no Worms with More Free Radicals Lived Longer bearing on how long they lived. 100 More recently, Siegfried Hekimi, a biol- ogist at McGill University, has bred round- Normal worms Mutant worms that produced worms that overproduce a specific free 80 high levels of free radicals radical known as superoxide. “I thought they were going to help us prove the theo- ry that oxidative stress causes aging,” 60 says Hekimi, who had predicted that the worms would die young. Instead he re- 40 ported in a 2010 paper in PLOS Biology that the engineered worms did not devel- Mutant worms op high levels of oxidative damage and

Worms That Survived (percent) Survived That Worms given antioxidants 20 that they lived, on average, 32 percent lon- ger than normal worms. Indeed, treating these genetically modified worms with 0 the antioxidant vitamin C prevented this 0 10 20 30 40 50 increase in life span. He­kimi speculates Days that superoxide acts not as a destructive molecule but as a protective signal in the worms’ bodies, turning up the expres- in a 2003 interview: aging must be driv- lived longer. (At high concentrations, sion of genes that help to repair cellular en by free radicals. however, the antioxidants had deleterious damage. Although free radicals had never be- effects.) Other scientists soon began test- In a follow-up experiment, Hekimi ex- fore been linked to aging, it made sense ing it, too. In 1969 researchers at Duke posed normal worms, from birth, to low to Harman that they might be the cul- University discovered the first antioxi- levels of a common weed-controlling her- prit. For one thing, he knew that ionizing dant enzyme produced inside the body— bicide that initiates free radical production radiation from x-rays and radioactive superoxide dismutase—and speculated in animals as well as plants. In the same bombs, which can be deadly, sparks the that it evolved to counter the deleterious 2010 paper he reported the counterintui- production of free radicals in the body. effects of free radical accumulation. With tive result: the toxin-bathed worms lived CAENORHABDITIS CAENORHABDITIS Studies at the time suggested that diets these new data, most biologists began ac- 58 percent longer than untreated worms. rich in food-based antioxidants muted cepting the idea. “If you work in aging, it’s Again, feeding the worms antioxidants radiation’s ill effects, suggesting—cor- like the air you breathe is the free radical quenched the toxin’s beneficial effects. Fi- rectly, as it turned out—that the radicals theory,” Gems says. “It’s ubiquitous, it’s in nally, in April 2012, he and his colleagues were a cause of those effects. Moreover, every textbook. Every paper seems to re- showed that knocking out, or deactivat- DECEMBER 2010 12; NO. 8, VOL. free radicals were normal by-products of fer to it either indirectly or directly.” ing, all five of the genes that code for su-

breathing and metabolism and built up Still, over time scientists had trouble peroxide dismutase enzymes in worms BIOLOGY, PLOS in the body over time. Because both cel- replicating some of Harman’s experimen- has virtually no effect on worm life span. lular damage and free radical levels in- tal findings. By the 1970s “there wasn’t a Do these discoveries mean that the creased with age, free radicals probably robust demonstration that feeding ani- free radical theory is flat-out wrong? Si- caused the damage that was responsible mals antioxidants really had an effect on mon Melov, a biochemist at the Buck In- for aging, Harman thought—and antioxi- life span,” Richardson says. He assumed stitute for Research on Aging in Novato, dants probably slowed it. that the conflicting experiments—which Calif., believes that the issue is unlikely Harman started testing his hypothe- had been done by other scientists—simply to be so simple; free radicals may be ben- ” BY WEN YNAG AND SIEGFRIED HEKIMI, IN AND SIEGFRIED HEKIMI, YNAG WEN BY ” sis. In one of his first experiments, he fed had not been controlled very well. Perhaps eficial in some contexts and dangerous in ,

mice antioxidants and showed that they the animals could not absorb the antioxi- others. Large amounts of oxidative dam- IN INCREASED LONGEVITY TRIGGERS SIGNAL SUPEROXIDE MITOCHONDRIAL “A SOURCE: ELEGANS

66 Scientific American, February 2013 © 2013 Scientific American age have indisputably been shown to these interventions affected overall levels their review to the trials that were least cause cancer and organ damage, and of oxidative damage, however, because likely to be affected by bias—those in plenty of evidence indicates that oxida- the investigators did not assess these which assignment of participants to their tive damage plays a role in the develop- changes. In 2010 researchers at the Uni- research arms was clearly random and ment of some chronic conditions, such as versity of California, San Francisco, and neither investigators nor participants heart disease. In addition, researchers at Pohang University of Science and Tech- knew who was getting what pill, for in- the University of Washington have dem- nology in South Korea reported in Cur- stance—they found that certain antioxi- onstrated that mice live longer when rent Biology that some free radicals turn dants were linked to an increased risk of they are genetically engineered to pro- on a gene called HIF-1 that is itself respon- death, in some cases by up to 16 percent. duce high levels of an antioxidant known sible for activating a number of genes in- Several U.S. organizations, including as catalase. Saying that something, like volved in cellular repair, including one the American Heart Association and the oxidative damage, contributes to aging that helps to repair mutated DNA. American Diabetes Association, now ad- in certain instances, however, is “a very Free radicals may also explain in part vise that people should not take antioxi- different thing than saying that it drives why exercise is beneficial. For years re- dant supplements except to treat a diag- the pathology,” Melov notes. Aging prob- searchers assumed that exercise was good nosed vitamin deficiency. “The literature ably is not a monolithic entity with a sin- in spite of the fact that it produces free is providing growing evidence that these gle cause and a single cure, he argues, radicals, not because of it. Yet in a 2009 supplements—in particular, at high dos- and it was wishful thinking to ever sup- study published in the Proceedings of the es—do not necessarily have the beneficial pose it was one. National Academy of Sciences USA, Mi- effects that they have been thought to,” chael Ristow, a nutrition professor at the says Demetrius Albanes, a senior investi- SHIFTING PERSPECTIVE Friedrich Schiller University of Jena in gator at the Nutritional Epidemiology Assuming free radicals accumulate dur- Germany, and his colleagues compared Branch of the National Cancer Institute. ing aging but do not necessarily cause it, the physiological profiles of exercisers Instead, he says, “we’ve become acutely what effects do they have? So far that who took antioxidants with exercisers aware of potential downsides.” question has led to more speculation who did not. Echoing Richardson’s results It is hard to imagine, however, that an- than definitive data. in mice, Ristow found that the exercisers tioxidants will ever fall out of favor com- “They’re actually part of the defense who did not pop vitamins were healthier pletely—or that most researchers who mechanism,” Hekimi asserts. Free radicals than those who did; among other things, study aging will become truly comfort- might, in some cases, be produced in re- the unsupplemented athletes showed able with the idea of beneficial free radi- sponse to cellular damage—as a way to fewer signs that they might develop type 2 cals without a lot more proof. Yet slowly, it signal the body’s own repair mechanisms, diabetes. Research by Beth Levine, a mi- seems, the evidence is beginning to sug- for example. In this scenario, free radicals crobiologist at the University of Texas gest that aging is far more intricate and are a consequence of age-related damage, Southwestern Medical Center, has shown complex than Harman imagined it to be not a cause of it. In large amounts, howev- that exercise also ramps up a biological nearly 60 years ago. Gems, for one, be- er, Hekimi says, free radicals may create process called autophagy, in which cells lieves the evidence points to a new theory damage as well. recycle worn-out bits of proteins and oth- in which aging stems from the overactivi- The general idea that minor insults er subcellular pieces. The tool used to di- ty of certain biological processes involved might help the body withstand bigger gest and disassemble the old molecules: in growth and reproduction. But no mat- ones is not new. Indeed, that is how mus- free radicals. Just to complicate matters a ter what idea (or ideas) scientists settle cles grow stronger in response to a bit, however, Levine’s research indicates on, moving forward, “the constant drill- steady increase in the amount of strain that autophagy also reduces the overall ing away of scientists at the facts is shift- that is placed on them. Many occasional level of free radicals, suggesting that the ing the field into a slightly stranger, but a athletes, on the other hand, have learned types and amounts of free radicals in dif- bit more real, place,” Gems says. “It’s an from painful firsthand experience that ferent parts of the cell may play various amazing breath of fresh air.” an abrupt increase in the physical de- roles, depending on the circumstances. mands they place on their body after a MORE TO EXPLORE long week of sitting at an office desk is THE ANTIOXIDANT MYTH Is the Oxidative Stress Theory of Ageing Dead? Viviana instead almost guaranteed to lead to If free radicals are not always bad, then I. Pérez et al. in Biochimica et Biophysica Acta, Vol. 1970, No. pulled calves and hamstrings, among their antidotes, antioxidants, may not al- 10, pages 1005–1014; October 2009. other significant injuries. ways be good—a worrisome possibility Biology of Aging: Research Today for a Healthier To- morrow. National Institute on Aging. National Institutes In 2002 researchers at the University given that 52 percent of Americans take of Health, November 2011. www.nia.nih.gov/health/ of Colorado at Boulder briefly exposed considerable doses of antioxidants daily, publication/biology-aging worms to heat or to chemicals that in- such as vitamin E and beta-carotene, in Alternative Perspectives on Aging in Caenorhabditis duced the production of free radicals, the form of multivitamin supplements. In elegans: Reactive Oxygen Species or Hyperfunction? David Gems and Yila de la Guardia in Antioxidants & Redox showing that the environmental stress- 2007 the Journal of the American Medical Signaling. Published online September 24, 2012. ors each boosted the worms’ ability to Association published a systematic review SCIENTIFIC AMERICAN ONLINE survive larger insults later. The interven- of 68 clinical trials, which concluded that To learn more about possible molecular causes of tions also increased the worms’ life ex- antioxidant supplements do not reduce aging, visit ScientificAmerican.com/feb2013/aging pectancy by 20 percent. It is unclear how risk of death. When the authors limited

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