WASHINGTON -- Vitamin C may help prevent the damage caused by second-hand tobacco smoke, offering a way for people to protect themselves from smokers in their lives, Reuters quoted U.S. researchers as saying on Tuesday.

A small study of 67 nonsmokers exposed to environmental smoke showed those who took 500mg of vitamin C daily had lower levels of a compound linked to the damage done by tobacco smoke.

The study did not last long enough to tell whether the vitamin takers were less likely to have cancer or heart disease, but Marion Dietrich of the University of California, Berkeley, who led the study, found the results encouraging.

"They show that vitamin C may help protect nonsmokers from the oxidative damage caused by second-hand tobacco smoke," Dietrich, a nutritional epidemiologist, said in a statement.

Oxidative damage has been compared to rust damaging metal. It is caused by charged particles known as free radicals, and can be counteracted by antioxidants including vitamin C.

But what works in a lab dish does not always hold true in the human body.

Writing in Tuesday's issue of the journal ***Nutrition and Cancer***, Dietrich and other researchers tested for levels of F2-isoprostanes, which are generated through a form of oxidative stress called lipid peroxidation.

This can damage the cell membrane and help form plaque that blocks arteries.

The 67 volunteers, all nonsmokers exposed to second-hand smoke, were randomly assigned to one of three groups.

One group took 500 mg of vitamin C a day, a second group took vitamin C, vitamin E and the antioxidant alpha-lipoic acid (ALA), and a third group took daily placebo capsules.

After two months, blood levels of F2-isoprostanes dropped by 11.4 percent for the vitamin C group compared with those taking the dummy capsule, and 12 percent for the C plus E plus ALA group. ---Vitamin E Added Little Benefit---

Adding E and ALA did not help much.

"That was a surprise to us," Gladys Block, a professor of nutritional epidemiology at Berkeley's School of Public Health who worked on the study, said in a telephone interview.

The volunteers were told not to take any other vitamins for several weeks before the study started, and people who reported eating plenty of fruits and vegetables were excluded.

"The evidence is overwhelmingly consistent that people who eat a lot of fruits and vegetables have a lower risk of cancer," Block said.

Such people may already have so many antioxidants in their system that they would not benefit from taking vitamins, she said.

Block said the group did a study last year that showed smokers could lower markers of oxidative damage by taking vitamin C.

But she said she hoped the findings would not lead people to think they can pop vitamins and escape the consequences of unhealthy habits.

"The message of the study is clearly not that taking vitamin C makes smoking or exposing others to smoke OK," she said. "But, if you are in a situation where you cannot escape frequent exposure to second-hand smoke, it may be worthwhile to take vitamin C supplements as a precautionary measure. And, as always, eat a diet rich in fruits and vegetables."