Maternal C-Reactive Protein and Schizophrenia

To the Editor: In their article published in the September 2014 issue of the Journal, Sarah Canetta, Ph.D., et al. (1) report that increasing maternal C-reactive protein levels, classified as a continuous variable, were significantly associated with schizophrenia in offspring (adjusted odds ratio reported in the abstract=1.31; 95% confidence interval [CI]=1.10–1.56; adjusted odds ratio reported in the results=1.28; 95% CI=1.07–1.54). The authors interpret this finding from Finland as evidence that maternal inflammation plays a role in this disorder and claim that this inflammation may be due to infections during pregnancy.

Surprisingly, the authors do not mention the possibility that the increased C-reactive protein levels were caused by maternal smoking. Levels of C-reactive protein are increased in smokers and remain elevated up to 5 years after cessation (2, 3). This is important because schizophrenia patients are more likely to have a mother who smoked during pregnancy (4). Moreover, smoking during pregnancy is relatively common in Finland. An investigation in 1997 found high prevalence rates among single (30%) and less educated (25%) pregnant women (5). Thus, the increase in maternal C-reactive protein levels may be due, at least in part, to smoking. The same considerations apply to the association, reported by the same research group, between maternal C-reactive protein and autism (6).

Finally, it is worth remembering that the results of studies on the relationship between prenatal infection and schizophrenia are not entirely consistent. Birth during the 9-month period after the 1957 influenza pandemic, which produced infection rates of about 50%, was not a risk factor for schizophrenia (7).