A new study has found the strongest evidence yet that smoke-free workplace laws that reduce secondhand smoke inhalation can lead to reductions in heart attacks.

The research, carried out by scientists at the Mayo Clinic in Rochester, Minn., found a 33 percent drop in heart attack rates in one Minnesota county after public smoking bans were enacted.

“I think the bottom line is this should turn the page on the chapter discussing whether or not secondhand smoke is a risk factor for heart attacks,” said Dr. Richard D. Hurt, an author of the study and a professor of medicine at Mayo.

Published in Archives of Internal Medicine, the study examined medical data in Olmsted County, which has a population of about 144,000, over two periods: the 18 months before the county banned smoking in restaurants in 2002, and the 18 months after it extended the ban to bars and all workplaces in 2007. Dr. Hurt and his colleagues found that while rates of hypertension, diabetes, high cholesterol and obesity remained constant or increased after the bans, the incidence of heart attacks dropped sharply.

Smoking rates declined in Minnesota between 2000 and 2010, from about 20 percent to 15 percent, but that change alone was not enough to explain the 33 percent drop in heart attacks, Dr. Hurt said.