Archive for February 17th, 2010

Posted on February 17, 2010 - by David

Anemia During Pregnancy: Another Trigger for Schizophrenia?

At the close of a 20 year long study, researchers from the University Hospital of Copenhagen claim that “children of mothers who had been diagnosed with anemia during pregnancy, most likely due to iron deficiency, had a significantly elevated risk of developing the mental disorder. ” You can check out the article where I first read about the findings, or look at an abstract of the research paper, published in the Schizophrenia Bulletin.

Once again, I find myself less than impressed with the analysis of the data gathered and the conclusions drawn. I quote the Reuters news article:

To further investigate this potential link, Srensen and colleagues analyzed the psychiatric outcomes of a large group of Danish children born between 1978 and 1998 — the biggest cohort in which the relationship has been examined. Each child was followed from age 10 until the onset of schizophrenia, death or the study’s closure on December 31, 2008.

Among 1,115,752 newborns, 17,940 (1.6 percent) were exposed to anemia in the womb. A total of 3,422 — including 41 from the exposed group — went on to develop schizophrenia, according to the report published in the journal Schizophrenia Bulletin.

After accounting for differences between the two groups and other relevant factors, including the parents’ ages and history of mental illness, exposure to anemia in the womb was associated with a 60 percent increased risk of schizophrenia in offspring during the 20 years of the study.

The researchers further concluded that 0.58 percent of schizophrenia cases (a total of about 20 diagnoses) could have been prevented had there been no cases of anemia among the mothers.

Now I don’t claim to be a statistician. I took two semesters of stat in college to fulfill my math requirement, and let’s just say my attendance wasn’t great. Still, I can’t seem to resist doing some of my own number crunching…

• 41 schizophrenics in the exposed group / 17,940 exposed to anemia = a prevalence rate for schizophrenia of approximately 0.2% for those exposed to anemia in the womb
• 3,422 total cases of schizophrenia – 41 exposed cases= 3381 schizophrenics not exposed
• 1,115,752 total children – 17,940 children exposed to anemia = 1,097,812 children not exposed
• 3381 / 1,097,812 = a prevalence rate for schizophrenia of approximately 0.3% for those not exposed to anemia in the womb

Obviously, 0.3% is greater than 0.2%, but after adjusting for potentially confounding factors, the researchers still arrive at the conclusion that “exposure to anemia in the womb was associated with a 60 percent increased risk of schizophrenia in offspring.” According to my best reading, this adjustment leaves them with only 20 cases of schizophrenia among those exposed to anemia which could not be attributed to some other factor. If the adjustments cut the number of the exposed cases in half, and they still determine that this group has a 60% greater risk of developing schizophrenia, then obviously the total number of schizophrenic cases they are working with has also been drastically reduced. It seems pretty bold to make this claim about increased risk on the basis of 20 cases, but my lack of statistical expertise probably renders me unqualified to make this judgment. Still, the simple fact that adjustment for confounding factors dramatically altered the size of the group is a little reminder of how many and how varied are the explanations for the cause of schizophrenia. Even if it’s true that about one half of one percent of all cases of schizophrenia can be attributed to iron deficiency anemia, does this really get us any closer to understanding the origins of this destructive mental illness?

A few last thoughts. According to my admittedly brief google research conducted this afternoon, iron deficiency is probably the most common nutritional deficit in the world, and I would assume that iron deficiency, (and therefore iron deficiency anemia), is more common in less developed parts of the world. So, if Iron Deficiency Anemia during pregnancy is a significant cause or contributor to the development of schizophrenia, then why aren’t the rates of schizophrenia higher in less developed countries? This line of reasoning would also suggest that rates of schizophrenia should have been higher centuries ago when diets were poorer and fewer resources were available, but it appears that this is not the case.