Posted 29 August 2011
A very interesting article by Dr Ben Goldacre, published in The Guardian.
“Trials show that people who think they’ve done something healthy, even if they haven’t, smoke more and believe they are invulnerable to diseases”
The article is reprinted below in the event readers are unable to link to the original.
You think you’ve done something healthy, so you permit yourself a ‘treat’.
We all have irrational fears – flying is plainly scarier than getting in a car – and we all have odd rituals that we use to manage them. But what if we believed our own hype about these rituals and became cocksure, perhaps even harming ourselves?
Here is a concrete example. In the study of risk perception, people talk about “the licensing effect”: when you take a vitamin pill, for example, you think you’ve done something healthy and wholesome, so you permit yourself to eat more chips and have a cigarette. It sounds like a nice idea, but a bit vague.
Two new experiments put flesh on these bones. Firstly, researchers took 74 undergraduates who were daily smokers, and divided them into two groups at random. The first group were given a dummy pill, a placebo, and were told just that: you’re in the control group, taking a dummy pill, with no active ingredient. The other participants were in the vitamin pill group: you’ve been given a vitamin pill, they were told.
But in fact, the researchers had lied. Everyone in the study got the same dummy pill, with no active ingredient. Half of them thought they’d had a health-giving vitamin pill, because the intention was to see whether people’s health behaviours change if they think they’ve had a nice, healthy vitamin pill.
After the pills, they were given a survey to fill out. Because it was Taiwan, where lots of people smoke, they were told: “This survey will take you about one hour to finish … you’re allowed to smoke if you want.”
The results were startling. Firstly, people who thought they’d had a vitamin pill gave different answers on the survey. These featured questions from the excellently titled Adolescent Invulnerability Scale (which has been reasonably well validated elsewhere), such as “Special problems, getting an illness or disease, are not likely to happen to me”, “I’m unlikely to be injured in an accident”, and so on. People who thought they’d had a vitamin pill rated themselves as generally more invulnerable.
The results for smoking were more worrying. There’s no doubt smoking is bad for you. There’s also no doubt the motives and justifications for smoking are complex. But people who thought they’d had a vitamin pill were 50% more likely to have a cigarette – 89% compared with 62% – and that result was highly statistically significant.
This might be a good moment to pause and remember that the Cochrane review on antioxidant vitamin pills – the pills that glossy magazines most like to recommend – found around 200,000 patients’ worth of good randomised trial data, and overall, these pills do nothing to prolong life: if anything, it turns out, they actively increase your risk of dying.
So back to our study on risk compensation behaviour. They broadened the design in case students are somehow an exceptional case, and repeated the experiment with 80 new participants, aged 19 to 58, from the wider community: once again, the people who thought they’d had vitamin pills smoked more cigarettes, and once again they believed themselves to be more invulnerable to harm.
So they expanded the project even further, into two longer studies, broader in remit, and this time people who thought they’d had a vitamin pill were less likely to exercise and less likely to choose healthier food.
People often ask what the harm is from quackery. I don’t think there needs to be one: quackery, overall, is more interesting than it is dangerous. But the message from these trials is clear. Believing, incorrectly, that you’ve done something healthy by taking a vitamin pill makes you more likely to take genuine, concrete, real-world risks with your health. It’s a chilling thought, but ideas aren’t without impact, and every time we humour a harmless myth – that vitamin pills are healthy, that some fashionable berry prevents cancer – we might be doing more harm than we think.
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A randomized experiment to examine unintended consequences of dietary supplement use among daily smokers: taking supplements reduces self-regulation of smoking
Wen-Bin Chiou1,*, Chin-Sheng Wan2, Wen-Hsiung Wu3,4, King-Teh Lee4 Article first published online: 2 AUG 2011 DOI: 10.1111/j.1360-0443.2011.03545.x
We examined whether smokers’ use of dietary supplements (e.g. vitamin C, multi-vitamins) induces illusory invulnerability that in turn disinhibits smoking. Such supplement use may be perceived as conferring health credentials.
A single-factor (credentials: with or without) between-subjects design was employed. Smokers were assigned randomly to take either a known placebo pill or a dietary supplement (in fact, the same placebo) in an ostensible health-food test.
Laboratory at Kaohsiung Medical University, Taiwan.
Study 1 involved of a student sample consisting of 74 daily smokers, whereas study 2 involved a community sample consisting of 80 daily smokers.
In Study 1, participants reported their perceived invulnerability following the manipulation. In study 2, pre- and post-test measures of invulnerability were administered, and attitudes towards dietary supplements were assessed prior to the manipulation. In both studies, the dependent measure was the number of cigarettes smoked during completion of an unrelated survey.
Participants who believed that they were taking a dietary supplement smoked more cigarettes than did controls. Study 1 found support for the role of perceived invulnerability as a mechanism underlying this effect.
Study 2 demonstrated the moderating effect played by attitudes towards dietary supplements: a more positive attitude towards supplements increased susceptibility to licensing effects.
Dietary supplement use may create illusory invulnerability, reducing the self-regulation of smoking. Reminding health-conscious smokers that multi-vitamins do not prevent cancer may help such smokers to control their smoking and encourage them to stop.
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Ironic Effects of Dietary Supplementation Illusory Invulnerability Created by Taking Dietary Supplements Licenses Health-Risk Behaviors
Wen-Bin Chiou1, Chao-Chin Yang2 and Chin-Sheng Wan3
1Institute of Education, National Sun Yat-Sen University 2Department of Chinese Culinary Arts, National Kaohsiung University of Hospitality and Tourism 3Department of Hospitality Management, Southern Taiwan University Wen-Bin Chiou, Institute of Education, National Sun Yat-Sen University, 70 Lien-Hai Rd., Kaohsiung, Taiwan 80424 E-mail:
The use of dietary supplements and the health status of individuals have an asymmetrical relationship: The growing market for dietary supplements appears not to be associated with an improvement in public health. Building on the notion of licensing, or the tendency for positive choices to license subsequent self-indulgent choices, we argue that because dietary supplements are perceived as conferring health advantages, use of such supplements may create an illusory sense of invulnerability that disinhibits unhealthy behaviors. In two experiments, participants who took placebo pills that they believed were dietary supplements exhibited the licensing effect across multiple forms of health-related behavior: They expressed less desire to engage in exercise and more desire to engage in hedonic activities (Experiment 1), expressed greater preference for a buffet over an organic meal (Experiment 1), and walked less to benefit their health (Experiment 2) compared with participants who were told the pills were a placebo. A mediational analysis indicated that perceived invulnerability was an underlying mechanism for these effects. Thus, a license associated with the use of dietary supplements may operate within cycles of behaviors that alternately protect and endanger health.
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Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases
Goran Bjelakovic1,*, Dimitrinka Nikolova2, Lise Lotte Gluud2, Rosa G Simonetti3, Christian Gluud2Editorial Group: Cochrane Hepato-Biliary Group
Published Online: 20 JAN 2010
Assessed as up-to-date: 19 FEB 2008
1Medical Faculty, University of Nis, Department of Internal Medicine – Gastroenterology and Hepatology, Nis, Serbia 2Copenhagen Trial Unit, Centre for Clinical Intervention Research, Department 3344, Rigshospitalet, Copenhagen University Hospital, Cochrane Hepato-Biliary Group, Copenhagen, Denmark 3Ospedale V.Cervello, Divisione di Medicina, Palermo, Italy
*Correspondence: Goran Bjelakovic, Medical Faculty, University of Nis, Department of Internal Medicine – Gastroenterology and Hepatology, Nis, Serbia
*Correspondence: Goran Bjelakovic, Department of Internal Medicine – Gastroenterology and Hepatology, Medical Faculty, University of Nis, Boulevard Dr Zorana Djindjica 81, Nis, 18000, Serbia. [email protected].
Animal and physiological research as well as observational studies suggest that antioxidant supplements may improve survival.
To assess the effect of antioxidant supplements on mortality in primary or secondary prevention randomised clinical trials.
We searched The Cochrane Library (Issue 3, 2005), MEDLINE (1966 to October 2005), EMBASE (1985 to October 2005), and the Science Citation Index Expanded (1945 to October 2005). We scanned bibliographies of relevant publications and wrote to pharmaceutical companies for additional trials.
We included all primary and secondary prevention randomised clinical trials on antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention. Included participants were either healthy (primary prevention trials) or had any disease (secondary prevention trials).
Data collection and analysis
Three authors extracted data. Trials with adequate randomisation, blinding, and follow-up were classified as having a low risk of bias.
Random-effects and fixed-effect meta-analyses were performed.
Random-effects meta-regression analyses were performed to assess sources of intertrial heterogeneity.
Sixty-seven randomised trials with 232,550 participants were included.
Forty-seven trials including 180,938 participants had low risk of bias.
Twenty-one trials included 164,439 healthy participants. Forty-six trials included 68111 participants with various diseases (gastrointestinal, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal, endocrinological, or unspecified). Overall, the antioxidant supplements had no significant effect on mortality in a random-effects meta-analysis (relative risk [RR] 1.02, 95% confidence interval [CI] 0.99 to 1.06), but significantly increased mortality in a fixed-effect model (RR 1.04, 95% CI 1.02 to 1.06). In meta-regression analysis, the risk of bias and type of antioxidant supplement were the only significant predictors of intertrial heterogeneity. In the trials with a low risk of bias, the antioxidant supplements significantly increased mortality (RR 1.05, 95% CI 1.02 to 1.08). When the different antioxidants were assessed separately, analyses including trials with a low risk of bias and excluding selenium trials found significantly increased mortality by vitamin A (RR 1.16, 95% CI 1.10 to 1.24), beta-carotene (RR 1.07, 95% CI 1.02 to 1.11), and vitamin E (RR 1.04, 95% CI 1.01 to 1.07), but no significant detrimental effect of vitamin C (RR 1.06, 95% CI 0.94 to 1.20). Low-bias risk trials on selenium found no significant effect on mortality (RR 0.90, 95% CI 0.80 to 1.01).
We found no evidence to support antioxidant supplements for primary or secondary prevention. Vitamin A, beta-carotene, and vitamin E may increase mortality. Future randomised trials could evaluate the potential effects of vitamin C and selenium for primary and secondary prevention. Such trials should be closely monitored for potential harmful effects. Antioxidant supplements need to be considered medicinal products and should undergo sufficient evaluation before marketing.
Plain language summary
No evidence to support antioxidant supplements to prevent mortality in healthy people or patients with various diseases