In a recent study from Taiwan, smokers who thought they had taken a vitamin pill smoked more afterwards, possibly from the belief that vitamins protect them from the harmful effect of cigarettes.

This type of behavior is called licensing: the belief that a healthy action allows a person to indulge in other unhealthy behaviors without having to pay the price. Morally, it allows people who perform a virtuous act to justify later ones that are less savory. In health, it can allow people who eat a salad for lunch to feel entitled to eat a double order of cheesecake for desert at dinner or even during the same lunch.

It's as if after doing a good deed for the day, the rest of the day becomes happy hour. It's fuzzy logic combined with fuzzy math. Yet nearly everyone does it at some time or other.

Smokers who thought they had taken a Vitamin C pill smoked nearly twice as many cigarettes as the other smokers. And they also reported greater feelings of invulnerability.

In the Taiwanese study, licensing appeared to be the cause of extra cigarette smoking.

In part one of the two-part study, 74 smokers were told that they were taking part in a health food test. All were given a placebo, an inactive pill, but half were told that it was a Vitamin C pill. After taking their pill, the smokers were all allowed to smoke freely as they answered an unrelated hour-long survey.

While filling out the survey, smokers who thought they had taken a Vitamin C pill smoked nearly twice as many cigarettes as the other smokers. And they also reported greater feelings of invulnerability.

In the second part, 80 smokers were given a Placebo, with half told they were taking a multivitamin. Afterwards, they were allowed to smoke while taking a survey that contained questions about their attitudes toward multivitamins. Once again, those who thought they took a vitamin pill smoked more cigarettes during the survey. And those who reported a greater belief in the health benefits of multivitamins reported greater feelings of invulnerability and smoked even more than their counterparts who were less optimistic about vitamin potency.

The chain of reasoning used by the smokers isn't clear. Vitamin C and multivitamins don't protect against cancer or other harmful effects of smoking. What is clear is that those who thought they took vitamins smoked more and may have felt that taking the vitamins permitted them to do so.

An online version of an article detailing the study was published by Addiction on August 2, 2011. The article will also appear in a future print issue of the journal.

The effects of licensing aren't limited to smokers. In an article published online by Psychological Science on July 15, researchers from the same Taiwanese laboratory performed similar experiments on non-smokers, half of whom thought they were taking a dietary supplement. Those who thought they took a dietary supplement expressed less desire to engage in exercise, did less walking and expressed a greater preference to eat at a buffet instead of eating an organic meal.

The researchers interpret these findings as a caution to those who take dietary supplements to guard against feelings of invulnerability. Dietary supplements don't turn people into Superman (or Superwoman) and don't protect them from the ill effects of other unhealthy behaviors.