April 29 (HealthDay News) -- Secondhand smoke not only damages the delicate cells that line blood vessels but also disrupts the body's natural repair mechanism for those cells, a new study shows.

The research was done because there still are skeptics who doubt the health value of public smoking bans, said study co-author Stanton A. Glantz, professor of medicine at the University of California, San Francisco, Center for Tobacco Control Research and Education.

"There still are some people out there saying these effects [from smoking bans], seen in terms of reduced heart attacks and an immediate drop in heart attacks, are just not feasible," Glantz said.

The findings were expected to be published in the May 6 issue of the Journal of the American College of Cardiology.

The new study tested the arterial effects of 30 minutes exposure to secondhand smoke on 10 young adult nonsmokers. The concentration of ambient smoke used was "about the level you would get in a bar," Glantz said.

The researchers did a number of detailed tests to measure the impact of that exposure on the endothelial cells that line blood vessels. These cells line the entire circulatory system and serve as a kind of interface between circulating blood and the interior of the vessel wall.

That endothelial cells are damaged by secondhand smoke was already known, Glantz said. However, "Everybody asks how long that effect persists, but nobody had studied that question," he said.

The answer, according to the study, is that "most of the effects persist for at least a day," Glantz said. "We only did 24 hours, because we thought they would be gone after 24 hours. They weren't."

There was also a clear negative effect on endothelial progenitor cells, which are produced in the bone marrow and circulate through the body. The progenitor cells' job is to seek out and repair endothelial damage.

Secondhand smoke exposure interfered with chemical signals that bring these progenitor cells to the sites of damage, Glantz said. "It wiped out the chemotaxis [direction signaling] for at least a day," he said. "We don't know how long the effect persists."

It's a "fascinating" study, said Dr. Norman H. Edelman, chief medical officer of the American Lung Association.

"We already know that exposure to secondhand smoke can cause endothelial changes," Edelman said. "The beginning of arterial disease is endothelial damage. What this study shows is that the cells that are essential in the repair of the endothelium are also affected by secondhand smoke."

The study comes as Atlantic City becomes the latest American community to ban smoking in public places, Edelman noted.

"The good news is that a little more than half of the country is now smoke-free," Glantz said. "The bad news is that a little more than half of the country is not smoke-free."

SOURCES: Stanton A. Glantz, Ph.D., professor, medicine, University of California, San Francisco; Norman H. Edelman, M.D., chief medical officer, American Lung Association; May 6, 2008, Journal of the American College of Cardiology