Researchers in Thailand believe that fish sauce may be a contributory factor in deaths while sleeping. Associate Professor Somporn Triamchaisri of Mahidol University said that although it was difficult to determine the cause of 'sleep death' in apparently healthy Asian men, fish sauce and other fermented foods appeared to play a part in the fatal illness. The danger appears to be linked to tyramine, a chemical that occurs naturally in foods that contain a large amount of yeast and has been linked to sudden rises in blood pressure and is found in fish sauce.