Giving up sweets and avoiding vitamins could help you live longer, German researchers said on Tuesday.

They found that restricting glucose - a simple sugar found in foods such as sweets that is a primary source of energy for the body - set off a process that extended the life span of some worms by up to 25%.

The key was boosting the level of "free radicals" - unstable molecules that can damage the body and which people often try to get rid of by consuming food or drinks rich in anti-oxidants such as vitamin E, they said in a study published in the journal Cell Metabolism.

Restricting glucose first spurred the worms to generate more free radicals, but then they quickly built up long-lasting defenses against them, said Michael Ristow, an endocrinologist at the University of Jena and the German Institute of Human Nutrition, who led the study. "During the process, the worm generates more free radicals, which activates defenses against free radicals within the worm," he said. "The bad thing in the end promotes something good." The body needs glucose, but taking in too much was unhealthy, Ristow said.

Scientists have long known that restricting calorie intake in worms and monkeys increases longevity, and the study narrowed that idea further, to glucose. The study also for the first time points to a possible reason why antioxidants - long thought to promote health - might do more harm than good, Ristow said. The German team used a chemical that blocked the worms' ability to process glucose in a treatment that extended their life span by up to 25%, the equivalent of 15 years in humans.

The worms unable to depend on glucose increased energy power sources in certain cells for fuel. That activity produced more free radicals, which in turn generated enzymes that strengthened long-time protection against the harmful molecules, Ristow said.