The California Environmental Protection Agency (CalEPA) has concluded from a research review that secondhand smoke can cause breast cancer, paving the way for stricter regulation of smoking in the state, USA Today reported Jan. 25.

CalEPA said that exposure to environmental tobacco smoke raises the breast cancer risk 68 percent or more among women under age 50. The state regulators were more convinced about the link to breast cancer than major health groups, which have not yet endorsed the findings.

"We're not disputing that there is a plausibility that secondhand smoke could cause breast cancer," said Harmon Eyre of the American Cancer Society. "All we're saying is that the evidence has just not reached that level."

But Cheryl Healton, president of the American Legacy Foundation, called the CalEPA research "the most careful analysis of the data up to the most current time frame that exists anywhere. It has gone substantially further than anything else."

The U.S. Surgeon General is expected to release a report on secondhand smoke this year, and may weigh in on breast cancer, as well.

CalEPA was the first regulatory agency to declare secondhand smoking a cause of heart disease, back in 1997.