This isn't new - but I thought it was intersting...
SCHIZOPHRENIA: Prevalence of illness unluck of the Irish; Where you live, what you eat may play roles
Schizophrenia Update, December 2002
By: Veronique Mandal Star Health-Science Reporter, Windsor Star
October 9, 2002 Wednesday Final Edition
Geography plays a role in the incidence of schizophrenia, scientists suspect.
American researcher Dr. E. Fuller Torrey discovered that southern Ireland has probably the highest incidence of the disease in the world -- four per cent of the population, compared to one per cent for the rest of the world.
...One factor being studied is potato consumption. When exposed to light, the potato produces a keloid called solanine which can cause gastrointestinal disturbances and psychotic symptoms, including hallucinations. Torrey says while it might sound far-fetched, in the 20th century it was proved that many people living in the southern U.S. were spending lifetimes in institutions for a mental illness which turned out to be pellegra, caused by a lack of the vitamin niacin.
Other countries with a high rate of schizophrenia include Croatia, a part of Yugoslavia and some of the Scandinavian nations. In other countries, such as New Guinea, Torrey says schizophrenia is hard to find. Low rates have also been found in Italy and Spain, as well as in most developing countries. Schizophrenia has also been hard to find in remote parts of Africa and Southeast Asia.
Rates are higher in India and Sri Lanka, with studies in India showing that the illness is more common among the upper castes -- those who are more educated and exposed to western technology.
http://www.schizophrenia.com/New/Dec2002/irishDec02.htm