Long working hours are associated with diabetes risk factors - work stress, sleep disturbances, depression and unhealthy lifestyle, and some studies have found long hours associated with increased risk for cardiovascular disease.
Researchers combined data from 19 published and unpublished studies on more than 222,000 men and women in several countries.
The analysis, published in The Lancet Diabetes & Endocrinology, found no effect of working hours in higher socio-economic groups. But in workers of lower socio-economic status, working more than 55 hours a week increased the risk for Type 2 diabetes by almost 30 per cent.
The association persisted after excluding shift workers and adjusting for age, sex, obesity and physical activity.