Take vitamin pill, eat cake. How supplements can encourage unhealthy behaviour

Have you ever had that feeling, after an energetic gym session, or perhaps a long walk, that you've earned the right to a mountainous slice of cake, or to lounge lazily in front of the telly? Psychologists call these licensing effects and a new study has documented a similar phenomenon following the simple act of taking a vitamin pill. The researchers say the finding could help explain why the explosive rise in the consumption of dietary supplements (approximately half the US population take them, according to recent data) has not led to a commensurate improvement in public health.

Wen-Bin Chiou and his colleagues gave an inert pill to 82 participants recruited via posters in the Taiwanese city of Kaohsiung. Half the participants were told it was a placebo; the other half were told it was a vitamin pill. They were instructed to suspend their usual intake of supplements, if any, for the duration of the study.

Afterwards, compared with placebo participants, the participants who thought they'd taken a vitamin pill rated indulgent but harmful activities like casual sex and excessive drinking as more desirable; healthy activities like yoga as less desirable; and they were more likely to choose a free coupon for a buffet meal, as opposed to a free coupon for a healthy organic meal (these associations held even after controlling for participants' usual intake of vitamin pills. Participants also said at the end that they hadn't guessed the purpose of the study).

The vitamin-takers also felt more invulnerable than the placebo participants, as revealed by their agreement with statements like "Nothing can harm me". Further analysis suggested that it was these feelings of invulnerability that mediated the association between taking a postulated vitamin pill and the unhealthy attitudes and decisions.

A second study with student recruits was similar to the first, but this time, participants who'd taken what they thought was a vitamin pill opted to walk a shorter distance to return a pedometer to a researcher located elsewhere on campus (even though they'd just been reminded of the health benefits of walking). Again, this association, between the vitamin pill and behaviour, was mediated by feelings of invulnerability.

"People who rely on dietary supplements for health protection may pay a hidden price: the curse of licensed self-indulgence," the researchers said. "Policy interventions that remind individuals to monitor the licensing effect may help translate the increased use of dietary supplements into improved public health."
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Chiou, W., Yang, C., and Wan, C. (2011). Ironic Effects of Dietary Supplementation: Illusory Invulnerability Created by Taking Dietary Supplements Licenses Health-Risk Behaviors. Psychological Science DOI: 10.1177/0956797611416253

This post was written by Christian Jarrett for the BPS Research Digest.