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Working long hours linked to higher diabetes risk — if the job is low paying and has low status

People who worked long hours in jobs with low pay and low status were almost a third more likely to develop type 2 diabetes than those who worked fewer hours.

People who work long hours — more than 55 hours per week — in a low-status and poorly paying job are 30 percent more likely to develop type 2 diabetes than people who work a “normal” schedule of 30 to 45 hours per week, according to a study published online last week in Lancet Diabetes & Endocrinology.

The increase in risk was observed even after taking into account such diabetes-related risk factors as age, obesity, physical inactivity, smoking and shift work.

People with high socioeconomic jobs who put in those same long hours were not found to be at increased risk, however.

As a commentary that accompanies the study points out, most public health efforts for preventing type 2 diabetes focus on reducing obesity and increasing physical activity. This study’s findings suggest that work-related factors — particularly work schedules — may also need to be addressed to reduce the incidence of diabetes both here in the U.S. and globally.

Diabetes statistics are sobering. Globally, an estimated 285 million people have type 2 diabetes, and that number is predicted to jump to 439 million by 2030. Last week, researchers at the Centers for Disease Control and Prevention reported that the incidence of type 2 diabetes appears to have plateaued in the U.S.  Yet it still remains unacceptably high. An estimated 8.3 percent of American adults aged 20 to 79 have the disease — a rate that has more than doubled since 1990, when it was 3.5 percent.

The CDC report also notes that the incidence of type 2 diabetes continues to climb among many subgroups of Americans, especially blacks, Hispanics and people with low levels of education.

A meta-analysis

As background information in the Lancet Diabetes & Endocrinology study explains, many previous studies have reported an association between long working hours and factors known to contribute to diabetes, such as physical inactivity, poor diet, stress, sleep problems and depression. But only a handful of studies have looked at the direct association between long working hours and the incidence of type 2 diabetes, and their results have been somewhat equivocal.

The authors of the current study decided to test the hypothesis that the reason those previous studies’ results didn’t agree was because the studies were looking at people working in different types of jobs. They searched the medical literature for the best studies conducted to date on the topic. They identified four published and 19 unpublished studies involving more than 222,000 men and women from the United States, the United Kingdom, Japan, Australia, Finland, Sweden and Denmark. They then pooled the data from all those studies.

An analysis of the entire group of 222,000 workers revealed that the risk of type 2 diabetes was the same for those working more than 55 hours as for those working 35 to 45 hours per week. But when the socioeconomic status of the workers’ jobs was taken into account, a different finding emerged. People who worked long hours in jobs with low pay and low status  — but not those who worked long hours in jobs with high pay and high status — were almost a third more likely to develop type 2 diabetes than those who worked fewer hours.

Possible reasons why

Why long working hours raises the risk of diabetes primarily in people doing low-status, low-paying jobs is unknown. It could be, say the authors of this study, that long hours in the work lives of people in such jobs are simply markers for other hardships that are having an effect on the workers’ health. Or it could be that people in low-paying jobs have less control over when they work their long hours, and thus those hours may be more disruptive to their pursuit of healthful behaviors, like getting a good night’s sleep.

Of course, this meta-analysis used data from observational studies, which means it is unable to prove cause and effect. Still, the findings are troubling, particularly given recent trends in work hours. U.S. workers, particularly those in the bottom wage brackets, have increased their work hours considerably over the past three decades. In 2007, the average U.S. worker devoted 1,868 hours to his or her job (or jobs), an increase of 181 hours (or 10.7 percent) from 1979, according to the Economic Policy Institute. That’s the equivalent of an extra 4.5 weeks per year.

And it’s even worse for workers in the lowest fifth of the wage distribution. In 2007, they were working 22 percent more hours than in 1979, an increase of more than 400 hours — or 10 weeks — per year.

You can read the Lancet Diabetes & Endocrinology study in full on the journal’s website.

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