Many New Yorkers are exposed to secondhand smoke despite the city’s tough antismoking laws, with more than half of all nonsmoking New York City residents having elevated levels of the nicotine byproduct cotinine in their blood, the New York Times reported April 8.

New research from the city’s health department shows that 56.7 percent of nonsmokers living in New York City had elevated cotinine levels in their blood, compared to the national average of 44.9 percent of nonsmokers. Nonsmokers of Asian descent were the most likely to have elevated cotinine levels.

However, nonsmokers exposed to secondhand smoke in other  parts of the country tend to have higher cotinine levels, which suggests that nonsmoking New Yorkers are breathing cigarette smoke more often because of the dense urban space they live in, but at lower levels.

New York health officials found the study’s findings “puzzling,” since the city has fewer smokers per capita than many other American cities (23.3 percent of New York City adults smoked when the study took place, compared to the national average of 29.7 percent).

“This is not what we expected,” said study author Thomas R. Frieden, commissioner of the city’s Department of Health and Mental Hygiene. “It is a shocking number.”

The researchers gathered data from adults 20 and older in 2004, more than one year after the Smoke Free Air Act of 2002, which prohibited smoking in city workplaces, bars and restaurants.

The findings were published online April 7, 2009 in the journal Nicotine & Tobacco Research.