People who work long hours are at an increased risk of developing type 2 diabetes, according to a recent study.

Researchers found that people working for more than 55 hours per week doing manual work or other low socioeconomic status jobs have a 30 percent greater risk of developing the chronic disease.

Analysis of data from four published studies and 19 studies with unpublished data involving more than 22,000 men and women from the United States, Europe, Japan, and Australia who were followed for an average of 7.6 years, found a similar risk of developing type 2 diabetes in people working more than 55 hours a week compared to those putting in a normal 35 to 40 hour week. However, the researchers noted significant differences when the results were looked at more closely.

"The pooling of all available studies on this topic allowed us to investigate the association between working hours and diabetes risk with greater precision than has been previously possible," researcher Mika Kivimäki said in a statement. "Although working long hours is unlikely to increase diabetes risk in everyone, health professionals should be aware that it is associated with a significantly increased risk in people doing low socioeconomic status jobs."

Further analyses revealed that individuals doing low socioeconomic status jobs who worked 55 hours or more per week had a roughly 30 percent increased risk of developing diabetes compared to their counterparts who worked between 35 and 40 hours a week, even after taking into account health behaviors such as smoking and physical activity, and other risk factors including age, sex, and obesity. This association remained strong even after excluding shift work, which has been shown to increase the risk of obesity and developing type 2 diabetes.

Researchers warn that further research is needed to identify the underlying mechanisms for the association between long working hours and diabetes in people doing low socioeconomic status jobs, but suggest a number of possible explanations, including working disruptive schedules that leave little time to take part in health restoring behaviors such as sleeping, unwinding, and exercise.

The findings were published in The Lancet Diabetes & Endocrinology.