Holocaust survivors are at higher risk for developing schizophrenia than people who never experienced that kind of trauma, according to a new study by researchers at the University of Haifa.

According to the study, Holocaust survivors who immigrated to Israel were diagnosed with schizophrenia at a rate of 27 percent higher than European immigrants who had arrived before the Holocaust. The study also showed that Holocaust survivors who were in utero when their mothers experienced the Holocaust and who were born into that reality were 41 percent more likely to develop schizophrenia than Israelis of European origin who did not experience the Holocaust.

The study, entitled “Exposure to genocide and the risk of schizophrenia,” was published in the journal Psychological Medicine. It was based on various databases, both medical and demographic, regarding some 114,000 Israelis who were born in 22 European countries from 1928-1945. The health and demographic statistics came from Health and Interior Ministry records from 1950 to 2014.

Prof. Stephen Z. Levine of the University of Haifa’s Department of Community Mental Health conducted the study with Prof. Itzhak Levav, a department colleague, and Dr. Yair Goldberg of the statistics department. “The exposure to the various traumas for long periods and the suffering the survivors underwent during the Holocaust raised the risk of developing schizophrenia,” explains Levine.

“In the professional literatures there is a dispute regarding the influence of exposure to the Holocaust,” says Levine. “There are those who argue that Holocaust survivors who survived are stronger, healthier people and we could thus anticipate that they would be at lower risk for developing schizophrenia. On the other hand, there are those who argue that following prolonged exposure to extreme trauma, Holocaust survivors are at greater risk for developing schizophrenia, and this study backs that argument.”

The general assumption is that there is some kind of genetic basis for schizophrenia, but along with that, scientists are at odds regarding the extent to which environmental factors influence the disease. Within the broad range of environmental risk factors, scientists are now looking at epigenetic influences – influences on gene expression whose source is environmental and not the result of changes to DNA.

The nearly 114,000 Israelis examined – 52 percent men and 48 percent women – were divided into two groups. The first were those who experienced the Holocaust directly and immigrated to Israel after World War II. The smaller control group included people who had immigrated to Israel before the Holocaust affected their country of origin but who had family and friends who had been through the war and were thus exposed to it indirectly.

“The reason we chose to investigate the link to schizophrenia specifically is because the validity of the Health Ministry’s diagnosis for this illness is extremely reliable, even compared to [that of] other mental illnesses,” says Levine.

As noted, the population that experienced the Holocaust directly had a 27 percent greater risk of developing schizophrenia than the group that had been exposed indirectly. Those at greatest risk for the disease were the ones whose mothers were pregnant with them during the Holocaust and were born into it; they were 41 percent more likely to develop schizophrenia than the control group.

“In general, the difference between the groups support the assumption that there was some injury done to Holocaust survivors that apparently expresses itself in this illness,” says Levine. “The idea of examining the link and its influence on Holocaust survivors who were in their mother’s womb during the Holocaust came from scientific studies that established that when the mother, and thus the fetus, experiences starvation, it raises the risk of developing schizophrenia.”