Shift work, long hours and blue-collar jobs are all associated with higher levels of obesity than regular hours, shorter hours and white-collar jobs, a Statistics Canada report says.

Men working longer hours (more than 40 per week) were more likely to be obese than regular full-time male workers (30 to 40 hours per week), and more men and women who work shifts were obese than regularly scheduled workers, the study said.

The stress caused by long and irregular hours may be the root of the higher obesity levels, author Jungwee Park suggested in the report, Obesity on the Job, which was released on Friday. But he also noted that unusual work schedules may themselves may make it harder to eat well.

White-collar workers include managers, professionals, technologists, administrative, financial and clerical employees, while blue-collar workers are in trades, transport or equipment operators, farming, forestry, fishing, mining, processing, manufacturing or utilities.

His study, based on 2005 data from two very large surveys, the Canadian Community Health Survey and the National Population Health Survey, also found that there are more obese men aged 35 to 54 with higher incomes than with lower incomes.

That may reflect "a greater frequency of dining out," Park said, citing another researcher's report.

However, obesity decreases among women as income goes up. "Women with low personal income were more likely to be obese than high-income earners." That may reflect cultural influences, Park said.

Across the board, low education levels "significantly" increased the chance of obesity, except among younger workers aged 18 to 34, Park said.

Workers aged 35 to 54 with less than a high school diploma were 1.6 times more likely to be obese than workers who had completed post-secondary education," Park said.

In common with other studies, Park found that obesity is increasing.

"In 2005, 15.7 per cent of employed Canadians aged 18 to 64, or more than two million people, were obese, up from 12.5 per cent in the mid-1990s."

The figures are lower than reported in the 25-year-long Canadian Community Health Survey. It found the adult rate of obesity was 14 per cent in 1979, rising to 23 per cent in 2004.

Park suggested that the rate among workers might be lower because obese workers may drop out of the labour force.

Obese was defined as people with a body mass index (a person’s weight in kilograms divided by the square of their height in metres) over 30, where 18.5 to 24.9 is defined as normal weight.