Auckland University scientist Dr Shiva Reddy said his research on mice strongly supported the theory that nitrates caused some type 1 diabetes. He gave tiny doses of a drug called streptozotocin to mice who were genetically prone to developing type 1 diabetes and to another group who were not prone.

The chemical is involved in a similar cellular pathway to nitrates and is known to destroy insulin- producing cells when given in large doses. Most mice in the first group quickly developed diabetes; few in the second did, and much more slowly.

Dr Reddy hopes to test the theory overseas in the next two years on human insulin-producing cells taken from the pancreas of an organ donor.

Diabetes researcher Professor Bob Elliott, of the biotech company Living Cell Technologies, said Dr Reddy was doing pioneering work on the disease which backed the nitrates theory. Dr Reddy was the first to do laboratory experiments underpinning overseas survey work that had suggested a link between the disease and nitrates.

Professor Elliott said a study in Iceland found a link between heavy consumption of nitrate-preserved meat by newly pregnant women in the month before Christmas and type 1 diabetes in the children.

Scientists in Melbourne had found a substance like streptozotocin on the skins of potatoes. "There are other possibilities, particularly for foods that are heavily processed."