This is another high-quality study from the National Centre for Register-based Research in Aarhus, Denmark. The researchers find that the yet-to-be-identified risk factor(s) associated with urban birth do not seem to have changed in magnitude over most of the last century. This is a very curious finding, and difficult to explain. The research community now has to generate candidate exposures that may underlie the urban-rural gradient. In light of (a) the large population-attributable risk that seems to be associated with this exposure, and (b) the fact that many nations are becoming increasingly urbanized, this task needs to be addressed with a sense of urgency.View all comments by John McGrath
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...
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 turned to IUDs, which did not cause bloating or the other nasty physical side effects of the pill. What IUDs did have was a hidden wicking string. Those strings were ladders for infection moving into the uterus. So when thinking of environmental factors at the level of the family, one has to ask broad-spectrum socioeconomic questions about what families were actually up against in the 1970s.
Birth control methods could also add insight into why schizophrenia was identified in the late 1800s, a time when women were moving into paid labor outside the home. It had been common knowledge since ancient times that any foreign object inserted into the uterus (IUD) would interfere with pregnancy. Working women had to limit the number of children they had. There was information-sharing among female coworkers.
Think about the implications of IUD use in Catholic countries such as Ireland, which has a high rate of schizophrenia. Catholic mothers of schizophrenics would be loath to discuss birth control methods used prior to or during the birth of a child born with schizophrenia. Moreover, during the Dalkon Shield scandal and IUD birth defect lawsuits of the 1970s and 1980s, the schizophrenias did not get any coverage because children born with these disorders hadn't reached the age of onset yet.
I am a parent of a second-born adult daughter suffering from schizophrenia. Families, especially mothers, do not want to go back to the days when it was said that bad mothering caused schizophrenia. Yet, we who carried these children to term have to ask ourselves what was different going into and throughout these pregnancies?
Skilled researchers need to formulate and ask probing questions about what the mother was exposed to prior to and during these pregnancies.
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