A study has linked working long hours at a manual labor job with a greater risk of developing Type 2 diabetes.

Researchers at the University of London reviewed results of four published studies and 19 unpublished data reports to analyze the effects of long working hours on Type 2 diabetes. The collective data analyzed about 222,120 men and women from multiple countries, The University Herald reported.

The data found a 30 percent greater risk of Type 2 diabetes in manual workers and employees at other low socioeconomic status jobs who put in more than 55 hours a week.

“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,” Mika Kivimaki, a professor of epidemiology said in a press release.

“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,” Kivimaki said.

Study authors took other health factors such as smoking, physical activity, age, sex and obesity into consideration and still found a 30 percent increased risk.

Researchers say more studies are needed to determine possible causes, but suggest a possible reason for the increased risk may be disruptive schedules that may make it difficult for employees to fit healthy behaviors into their routine.