Does the overproduction of 5-HT(serotonin) and platelets cause autism? People from Binh Dinh and Phu Yen Provinces eat a lot of tuna (cá ngừ), which is rich in vitamin B12 that would increase platelet count (coagulants) and serotonin. Autism is the opposite of depression? High serotonin vs low serotonin?