Called “the licensing effect”, the study intended to show whether people’s behaviours change if they think they’ve had a nice, healthy vitamin pill.

The results were startling – people rated themselves as having better health on the survey they took and were 50 per cent more likely to have a cigarette afterwards than those who didn’t believe they’d had a vitamin pill. The researchers had, in fact, given everyone a placebo.

There’s no harm in taking vitamin supplements when you’re deficient, but don't expect them to bail you out of trouble.

“Multivitamin pills are in no way an insurance against poor health,” says Dr Dee Chohan, an emergency doctor.