POPs are most likely to come from eating fatty fish such as salmon. The study, of 196 fishermen and their wives, is published in the. POPs are a family of toxic chemicals that includes polychlorinated biphenyls (PCBs) and the insecticide DDT. They are by-products of industrial and agricultural processes and are widespread in the environment.

The Lund team analyzed blood samples from the volunteers for levels of a POP residue called CB-153, and DDE, the main by-product of DDT. Significantly higher levels of both chemicals were found in the blood of the 6% of men and 5% of women who had type 2 diabetes.

Previous research has suggested that toxic chemicals like POPs may decrease the ability of the body's cells to take up glucose. Another theory is that the chemicals may trigger complex interactions which disrupt the body's ability to break down fats.

Researcher Dr Lars Hagmar stated that, “people should not worry about eating oily fish.” He said the fishermen and their wives in the study were exposed to exceptionally high levels of pollutants. The Baltic coast, where they ply their trade, had been heavily polluted with POPs from industry, he said. The water was also shallow and cold, meaning that pollutants took a long time to start to degrade. The Baltic Sea was also surrounded by land with relatively little circulation of its waters, so pollutants were not as readily dispersed as they were in other bodies of water.

Amanda Eden, a care advisor at Diabetes UK, said: "While this study looks interesting, more extensive research is required before we can draw any firm conclusions of a link between these toxins and Type 2 diabetes. "What we do know is that, a healthy, balanced diet and regular physical activity can help reduce the risk of developing Type 2 diabetes.

"We also recommend that people aim to eat oily fish such as salmon or mackerel twice a week as part of a healthy, balanced diet."