They noticed that, although the popularity of dietary supplements was increasing, levels of general health had remained the same.

Inspired by the observation that a colleague chose an unhealthy meal over an organic dish simply because he had taken a multivitamin earlier in the day, Wen-Bin Chiou  of National Sun Yat-Sen University in Taiwan decided to research  the topic. One group of volunteers was told to take a multivitamin pill and the second a dummy pill while their lifestyle choices were monitored.

In reality, both groups had been given placebos.

The researchers found that those who believed they had taken a supplement felt immune to health hazards and were less likely to go for a walk to benefit their health.

They were also more likely to choose a buffet meal over a healthier organic one.

Chiou, whose research will be published in the journal Psychological Science, said, “After taking dietary supplements in the  morning, individuals should diligently monitor whether illusory invulnerability is activated by restored health credentials and subsequently licenses health-risk behaviors.”

A spokesman for the research team added, “To put it simply, people who take dietary supplements may have the misconception that they are invulnerable to health problems and may make poor decisions when it comes to their health, such as choosing fast food over a healthy and organic meal.”

However, experts said that several British studies had come to the opposite conclusion.

Dr Carrie Ruxton, of the industry-funded Health Supplements Information Service, said, “One of the big bugbears is that people who could really do with taking vitamins and minerals are a bit reluctant to do so for some reason, whereas the ones who are doing relatively well with their diets are the ones that add vitamins and minerals on top.”

From the April 25, 2011, Prepared Foods' Daily News.