ATLANTA - Nearly half of nonsmoking Americans are still breathing in cigarette fumes, but the percentage has declined dramatically since the early 1990s, a government study released yesterday showed.
The growing number of laws and policies that ban smoking in workplaces, bars, restaurants, and other public places is a main reason for the drop in secondhand smoke, researchers with the Centers for Disease Control and Prevention said.
Another factor is the drop in the number of adult smokers, which has inched below 20 percent, according to '07 CDC data.
The study found about 46 percent of nonsmokers had nicotine signs in their blood in tests done from 1999 through 2004. That was a steep fall from 84 percent when similar tests were done in the late 1980s and early 1990s.
Health officials weren't celebrating. "It's still high," said Cinzia Marano, one of the authors of the study published in a CDC publication, Morbidity and Mortality Weekly Report. "There is no safe level of exposure."
Cigarettes cause lung cancer and other lethal illnesses not only in smokers, but also in nonsmokers who breathe in smoke, studies have shown.
For nonsmoking adults, secondhand smoke raises their lung-cancer risk by at least 20 percent and their heart-disease risk by at least 25 percent. Children exposed to smoke are at higher risks of asthma, ear problems, acute respiratory infections, and sudden infant death syndrome, health officials say.
The new CDC report drew its data from the National Health and Nutrition Examination Survey, a government study that asks participants about their health and does blood tests and physical exams.
The blood tests check for cotinine - a nicotine byproduct that usually is detectable for up to four to five days. The tests are important, because many underestimate their exposure to secondhand smoke, Terry Pechacek, associate director for science in the CDC's Office on Smoking and Health, said.
The report focused on data collected on about 17,000 nonsmokers in the years 1988 through 1994, and about the same number in 1999 through 2004. People ages 4 and older were included.
The drop in secondhand-smoke exposure was not as dramatic in black nonsmokers as it was in whites and Mexican-Americans. The proportion of blacks with recent tobacco-smoke exposure dropped from 94 percent to about 71 percent; whites, from 83 percent to 43 percent, and for Mexican-Americans, 78 percent to 40 percent.
Also troubling - children's exposures did not fall as dramatically as it did for adults. More than 60 percent of children 4 through 11 had recent exposure to cigarette smoke in the 1999-2004 period, researchers found.
"Obviously, the exposure is at home," said Thomas Glynn, the American Cancer Society's chief of cancer science and trends.
Some parents are probably not smoking much less at home or in their cars, which would explain why their children's exposure did not fall as much as that of other children, CDC officials said. "Parents need to be aware that this is very dangerous, and they need to take actions to ensure that their children are not exposed," Mr. Pechacek said.