Far fewer Americans are exposed to secondhand smoke than a decade ago, a Centers for Disease Control and Prevention (CDC) study finds, and health advocates say that the findings show the need for more states to ban indoor smoking.

The Associated Press reported July 10 that the report found that 46 percent of U.S. nonsmokers had biomarkers for nicotine exposure in the blood in tests conducted between 1999 and 2004, down from 84 percent in samples gathered in the late 1980s and early 1990s.

The CDC said the decline was due to indoor-smoking bans and the overall decline in smoking in the U.S. Researchers found that secondhand-smoke exposure declined more significantly among whites and Hispanics than among blacks, and that 60 percent of children ages 4-11 were still being exposed, likely at home.

The study was based on levels of cotinine, a nicotine metabolite, in the blood of participants in the National Health and Nutrition Examination Survey.

"The dramatic decline in youth smoking since 1997 is powerful proof that scientifically proven measures, implemented primarily at the state and local level, are working," said Matthew Myers, president of the Campaign for Tobacco-Free Kids. "These include higher cigarette prices resulting from state cigarette tax increases and the 1998 state tobacco settlement; a growing number of state and local laws requiring smoke-free workplaces and public places; and effective, well-funded tobacco prevention programs run by the states and nationally by the American Legacy Foundation."