Scientists say people are at higher risk of Type 2 diabetes if they smoke or are victims of passive smoking.

In those who quit, the risk decreases over time, the research shows.

Scientists pooled together the results of 88 studies which between them had nearly six million participants.

Compared with never smoking, a current habit raised the risk of Type 2 diabetes by 37 per cent, passive smoking was associated with a 22 per cent increased risk and former smoking with a 14 per cent increased risk.

The findings are published in The Lancet Diabetes & Endocrinology journal.

Authors said that a short-term increased risk of diabetes seen in recent quitters needed to be further investigated.