People working long hours in manual or other low socioeconomic status jobs have a much higher risk of developing type 2 diabetes, a new study has found.

Researchers in the UK carried out a detailed analysis of 23 studies which looked at the effects of long working hours on type 2 diabetes.

The studies involved over 222,000 men and women from Europe, the US, Japan and Australia, all of whom were monitored for an average of seven years.

The researchers found that people who worked 55 hours or more in low socioeconomic status jobs had a 30% increased risk of developing type 2 diabetes compared to their counterparts who worked between 35 and 40 hours per week.

These results stood even when other factors that can affect diabetes risk were taken into account such as age, obesity and smoking.

The link also remained when shift work was excluded from the results. Shift work has been shown in other studies to increase the risk of obesity and type 2 diabetes.

The researchers believe more studies are needed to determine why working long hours in certain types of jobs appear to increase the risk of diabetes. However, they suggested that disruptive schedules could leave people with little time to unwind and exercise and could also affect sleep.

"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. 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," commented Prof Mika Kivimaki of University College London.

Details of these findings are published in the journal, The Lancet Diabetes & Endocrinology.