Experts suggest this could be due to Vitamin A – a substance which is found in animal foods and dairy products.
The vitamin boosts cells in the pancreas that produce the blood sugar-regulating hormone insulin, researchers said.
There has previously been no known link between diabetes and Vitamin A – which is found in liver, oily fish and cheese – until now.
Dr Albert Salehi, senior researcher at the Lund University Diabetes Centre in Sweden, said vitamin A is found mainly in offal and dairy products.
The researchers said milk in Sweden is enriched with Vitamin A and there appears to be no deficiency in people who eat a varied diet.
However he said some vegetarians perhaps need to be aware of the problem.
The research team from King’s College London and the Oxford Centre for Diabetes found the vitamin improves the function of the specialist cells – known as beta cells.
They initially discovered the cells contain a large quantity of a cell surface receptor for vitamin A.
Dr Salehi said: “There are no unnecessary surface receptors in human cells. They all serve a purpose but which, in many cases, is still unknown and because of that they are called ‘orphan’ receptors.
“When we discovered insulin cells have a cell surface expressed receptor for…