About 17 per cent of Canadians over the age of 12 are considered obese. (Kirsty Wigglesworth/Associated Press)

Obesity is emerging as a greater threat to public health than smoking, a U.S. study suggests.

The largest ongoing health survey interviewed more than 3.5 million American adults every year from 1993 to 2008.

As smoking rates tailed off in the U.S., the proportion of smokers among American adults fell from 22.7 per cent in 1993 to 18 per cent in 2008, while obesity rates rose from 14.5 per cent to 26.7 per cent over the same time period.

"This study estimated the overall burden of smoking and obesity over time and results indicate that because of the marked increase in the proportion of obese people, obesity has become an equal, if not greater, contributor to the burden of disease than smoking," Haomiao Jia of Columbia University and Dr. Erica Lubetkin of the City University of New York, concluded in the February issue of the American Journal of Preventive Medicine.

Such data are important for setting targets to reduce health risks of obesity, they said.

"I think what the study is showing is that the burden to society from obesity is probably greater than that of tobacco use, which has been the yardstick that people used," said Dr. Mark Tremblay, an international expert in child obesity research at the Children’s Hospital of Eastern Ontario in Ottawa.

The burden to society from tobacco use is also substantial, Tremblay said in cautioning against pitting smoking against obesity.

"We can no longer wait to act on strategies to put in place to promote healthy, active living in Canada, and prevent further increases in obesity," he added.

The study was based on interviews and calculations of the number of quality-adjusted life years (QALYs) lost to obesity and smoking.

Self-scoring system

Quality-adjusted life year measurements allow a person to state their own views on quality of life, with higher scores assigned for perfect or good health, and lower scores for illness, injury and death.

Over the study period, smoking-related QALYs lost were relatively stable at 0.0438 QALYs lost per population and 0.0464 QALYs were lost to obesity. Smoking had a bigger impact on deaths while obesity had a bigger impact on illness, the researchers found.

Such extensive studies haven't been conducted in Canada.

In 2008, Statistics Canada reported that 51 per cent of Canadians over the age of 12 were overweight or obese, and 17 per cent were obese, based in self reports of heights and weights. The highest rates were among 55- to 64-year-olds, with 22 per cent in that age group wrestling with excess weight.

A study presented in October at the Canadian Cardiovascular Congress in Edmonton found obesity, high blood pressure and high cholesterol are hitting Canadian teens at alarmingly high rates and are increasing.

"This generation of children will have shorter lifespans than their parents," said Dr. Glenn Berall, who specializes in treating childhood obesity at North York General Hospital in Toronto. "They will die sooner because of obesity."

Health experts say successful anti-smoking campaigns should be adapted for fighting obesity to help Americans and Canadians face aggressive marketing for fast food and couch-potato lifestyles.