CHICAGO —  A study finds smoking rates in some adults have dropped sharply in the past three decades, with greater decreases among adults with higher incomes and more education.

The University of Minnesota study looked at the smoking trends in adults aged 25-to-74 in the Minneapolis/St. Paul area from 1980 to 2009.

Researchers found the number of current smokers was cut in half, decreasing from nearly 33 per cent to 15.5 per cent in men and from nearly 33 per cent to about 12 per cent in women.

The study also found current smokers were smoking less, with the age-adjusted average number of cigarettes smoked per day decreased from about 23 to 13 in men and about 21 to 10 in women, and that fewer Americans were picking up the habit.

The research is part of the Minnesota Heart Survey, a population-based, cross-sectional study of trends in cardiovascular risk factors and included between 3,000 and 6,000 participants in each of its six surveys.

The study was funded by the U.S. National Institutes of Health, the Heart and Stroke Foundation of Canada, and the Quebec Foundation for Health Research, and was presented Sunday at the American Heart Association's annual meeting in Chicago.

The study's lead author, Kristian B. Filion of the epidemiology and community health division at the University of Minnesota, says the study didn't address the impact of legislative changes such as increases in cigarette taxes.

Smoking cessation efforts have made an impact, but more emphasis needs to be placed on people in lower income brackets and those with less education, Filion said in a news release on the American Heart Association's website.

"This group may not have the same access to medical care or the public health messages in the news media just aren't reaching them," he said.

"The prevalence of smoking has been decreasing, but it remains a public health issue. We need to have a better grasp on designing specific interventions for specific groups. A one-size-fits-all approach to stop smoking may not be as successful in some groups," Filion said.