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Pedersen CB, Mortensen PB. Are the cause(s) responsible for urban-rural differences in schizophrenia risk rooted in families or in individuals? Am J Epidemiol . 2006 Jun 1 ; 163(11):971-8. PubMed Abstract

Comments on Paper and Primary News
Comment by:  Elizabeth Cantor-Graae
Submitted 19 May 2006 Posted 19 May 2006
  I recommend this paper

Using a creative epidemiological approach, the authors take the urban-rural phenomenon one step higher and examine the risk associated with the birthplace of the older sibling. Their observation that the risk conferred by urban birth persists even after the family has moved to a rural area sugggests that familial influences play an important role in the "urban" effect.

View all comments by Elizabeth Cantor-Graae

Comment by:  John McGrath, SRF Advisor
Submitted 3 June 2006 Posted 4 June 2006
  I recommend this paper

This paper needs to be read carefully. It is worth the effort as the methods and results are very thought-provoking. The study uses variables available in Danish registers (i.e., place of birth of next eldest sibling) to tease out more clues about the association between urbanicity of birth and risk of schizophrenia. The cause (or causes) underlying the urban birth/residence risk factor remain stubbornly obscure. The new study suggests that candidate exposures should also be drawn from factors operating at the “family level” (i.e., where did the family reside before the affected individual was born/conceived). Some researchers will default to tortuous selective-migration theories to explain these results. However, the findings can also provide clues to help generate candidate environmental factors. The study forces us to address new questions. When is the critical window of exposure? After exposure, what is the duration of the risk period? For example, perhaps maternal and/or paternal exposures that are more likely to be acquired in cities (e.g., nutritional factors, toxins,...  Read more

View all comments by John McGrath

Primary News: Urban Schizophrenia Risk: A Family Affair?

Comment by:  Patricia Estani
Submitted 13 June 2006 Posted 13 June 2006
  I recommend this paper

Primary News: Urban Schizophrenia Risk: A Family Affair?

Comment by:  Ella Matthews
Submitted 16 June 2006 Posted 5 July 2006

Questions on the different rates of occurrence of the schizophrenia spectrum of brain disorders between northern (developed) and southern underdeveloped countries, between urban and rural, as well as the birth order within the family of those suffering from schizophrenia are important ones.

However, when thinking about family exposure to environmental factors, I think that there is much to learn from social science. Say that a 1970s family moved from the country to the city just at the time when the birth control pill had been developed and began to be widely available in urban industrialized areas: Estrogen levels on the early formulations of the "pill" were too high, causing women to search for other legal birth control methods which they could tolerate more easily. About the only other things that doctors could offer women back then were the highly touted IUDs.

Say also that a woman tried the birth control pill but, because her taking of the pill was spotty, she became pregnant with her first child. After delivering their first children, many 1970s women then...  Read more

View all comments by Ella Matthews

Comment by:  Karl-Ludvig Reichelt (Disclosure)
Submitted 11 July 2006 Posted 12 July 2006

The usual reason for moving to the city/urban environment is poverty. In the beginning of their existence in urban surroundings, such families remain poor and probably have a change in diet. More grains and less of yams, casava, vegetables, etc., which are more expensive in urban settings. This is especially pronounced when moving to Western countries from the developing nations. In industrialized countries the only "cheap" food is usually milk and bread. There, this difference becomes even more pronounced, and rates of schizophrenic development are several times higher than in natives in the same economic group.


Dohan FC, Harper EH, Clark MH, Rodrigue RB, Zigas V. Is schizophrenia rare if grain is rare? Biol Psychiatry. 1984 Mar;19(3):385-99. Abstract

Lorenz K. (1990) Cereals and schizophrenia. Adv Cereal Sci Technol X:435-469.

For a comprehensive discussion see
Reichelt KL, Seim AR, Reichelt WH. Could schizophrenia be reasonably explained by Dohan's hypothesis on genetic interaction with a dietary peptide overload? Prog Neuropsychopharmacol Biol Psychiatry. 1996 Oct;20(7):1083-114. Review. Abstract

View all comments by Karl-Ludvig Reichelt

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