Background A diagnosis of diabetes has been shown to be a risk factor for suicide in selected studies. The link between blood glucose and future suicide has yet to be examined.

Aim To examine if diabetes and blood glucose level are associated with a raised risk of suicide.

Methods The Korean Cancer Prevention Study is a cohort of 1 329 525 individuals (482 618 women) aged 30–95 years at baseline. A fasting serum specimen was assayed for blood glucose, and diabetes status was categorised into five groups based on existing definitions. Study members were followed for mortality experience over 14 years.

Results There were 472 suicide deaths (389 in men and 83 in women) during the follow-up. In men, there was a ‘J’-shaped diabetes–suicide death relation. Thus, while the highest suicide rates were apparent in those with type 2 diabetes and there was an incremental fall in suicide risk with decreasing blood glucose level, an inflection was seen in the low-normal group. Similar results were apparent in women, although there was no raised risk in the lowest blood glucose group.

Conclusion In the present cohort, diabetes (both existing and study detected) but not raised blood glucose was a risk factor for completed suicide.