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Environmental Factors May Be Additional Cause of Schizophrenia

It has been long established that heredity and genetics are huge factors in schizophrenia risk. But this study shows that environment also plays a significant role. “The literature suggests a big genetic component, but genes and environmental interaction is extremely complicated. We need to find the mechanism through which income actually matters,” explains Richard G. Frank, PhD, a professor of health economics at Harvard Medical School in Boston, who wrote an editorial in the same issue of JAMA Psychiatry about the implications of this study. RELATED: Early Treatment Programs for Precursors to Schizophrenia Multiply

Developing Schizophrenia: Children Born Into Poverty Appear to Face Greater Risk

In this study, researchers looked at data from everyone born in Denmark from 1980 to 2000 to assess associations between the risk of schizophrenia and parental income. Children were followed from their 15th birthday until schizophrenia diagnosis, emigration, death, or December 31, 2016 — whichever came first. The study found that 7,544 out of 1,051,033 (about 0.7 percent) were diagnosed at some point as schizophrenic, and of those, 54.7 percent were male. The adjusted hazard ratio was around double for children in the bottom quintile relative to those in the top. It also showed that being poor at birth has an especially negative effect.

When Income Increases, Schizophrenia Risk Decreases

The longer the cohort members were in a low-income state growing up, the higher their likelihood of developing schizophrenia. If at any point they moved into a higher income level, the risk was diminished. In cases where high income families transitioned to lower income levels the results were complicated; it’s a chicken and egg kind of scenario. Did the downward slide occur because the family was struggling to deal with a member’s schizophrenia and symptoms or was the disorder caused by the drop in financial stability?

Relative Poverty Is Also an Important Factor

Earlier research published in New Zealand Journal of Psychology found that it’s not just poverty that affects schizophrenia risk, but relative poverty, when people don’t have the minimum amount of income needed in order to reach the average standard of living in their particular society. This figure can change over time. RELATED: What Is Resilience? Your Guide to Facing Life’s Challenges, Adversities, and Crises

A number of mechanisms are likely driving the association, says the lead study author, Christian Hakulinen, PhD, a postdoctoral researcher in the department of psychology and logopedics at the University of Helsinki, in Finland: “For example, children from poor families are more likely than those from affluent backgrounds to experience other familial difficulties such as physical and emotional conflicts. This could raise the risk of child abuse, which has been linked with increased risk for subsequently developing psychosis. Similarly, psychosocial risk factors are known to accumulate in families with lower socioeconomic conditions. Of course, early factors are also of importance. For example, maternal infections and obstetric complications, which are more common with mothers from lower socioeconomic conditions, influence early neurodevelopment, which is then linked with increased schizophrenia risks.” RELATED: Schizophrenia and Pregnancy: What to Know

Poverty Affects Parents’ Ability to Protect Children From Toxic Stress

Dr. Frank says, “There is a lot of research saying that stress has a very negative effect on kids’ psychosocial development. Both resources and parental time can serve to protect kids facing toxic stress. When parents have low incomes, it can mean inconsistent schedules because parents have to work long hours and multiple jobs, and they may not be able to afford quality daycare. All that can get in the way of potentially good parenting.” RELATED: Bruce McEwen, PhD: Q&A on Your Body on Stress

The study is important because it shows the association, which allows researchers now to look at the mechanisms that are driving the data. “In the future, it would be important to study these mechanisms in more detail, for example using early brain imaging data, and also to see whether these associations differ according to genetic information; for example, whether the associations are stronger for those individuals who have higher genetic risk of schizophrenia,” says Dr. Hakulinen. Frank says, “Once we get that piece of the puzzle, we’ll see where public resources are needed most and be able to target people at risk.”