Increased Dietary Inflammatory Index Is Associated with Schizophrenia: Results of a Case–Control Study from Bahrain

Background: Several studies have indicated that chronic low-grade inflammation is associated with the development of schizophrenia. Given the role of diet in modulating inflammatory markers, excessive caloric intake and increased consumption of pro-inflammatory components such as calorie-dense, nutrient-sparse foods may contribute toward increased rates of schizophrenia. This study aimed to examine the association between dietary inflammation, as measured by the dietary inflammatory index (DII^®), and schizophrenia. Methods: A total of 120 cases attending the out-patient department in the Psychiatric Hospital/Bahrain were recruited, along with 120 healthy controls matched on age and sex. The energy-adjusted DII (E-DII) was computed based on dietary intake assessed using a comprehensive food frequency questionnaire (FFQ). Logistic regression was used to estimate odds ratios and 95% confidence intervals, adjusting for potential confounders including age, sex, body mass index, education, employment, diabetes, hypertension, and cardiovascular disease with E-DII expressed both as a continuous variable and categorized as quartiles. Results: The mean E-DII score for the entire sample was 1.79 ± 1.52, indicating a generally pro-inflammatory diet. The cases with schizophrenia appeared to have a higher E-DII score compared to controls: 1.99 ± 1.39 vs. 1.60 ± 1.38, respectively (p = 0.009). For every one unit increase in the E-DII score, the odds of having schizophrenia increased by 62% (OR 1.62; 95% CI 1.17–2.26). Similarly, increased risk was observed when the E-DII was used as quartiles, with participants in most pro-inflammatory quartile 4 being nearly 6 times more likely to be schizophrenic than participants in the most anti-inflammatory group quartile 1 (OR 5.96; 1.74–20.38; p-trend = 0.01). Conclusions: The data suggest that a pro-inflammatory diet, as indicated by increasing E-DII score, is associated with schizophrenia. This is the first study to examine the association between the DII and schizophrenia in a Middle Eastern population. Although these results are consistent with findings from research conducted in depression, additional studies are required before generalizing the findings to other populations.