Clinical depression is a widespread global problem with over 350 million people affected. Extensive research has been completed on potential treatment options, and though there has been some success, it has become apparent that symptom-directed approaches fail to address the condition as a whole. Accordingly, it is now paramount that prevention measures take precedence in future investigations of clinical depression. A recent study by Tasnime N. Akbaraly and colleagues examines the possibility that recurrent depressive symptoms are linked with an inflammatory response (a complex combination of immune system, blood vessel and chemical reactions) to dietary substances.

Published in 2016 by Clinical Psychological Science, the investigation is based on existing evidence that connects poor diets with depression. These sources identified excessive amounts of two chemical markers of inflammation in people with depression: interleukin-6 (IL-6) and C-reactive protein (CRP). It was therefore proposed that the association between depressive symptoms and poor diet may be at least partially explained by immune responses to nutritional content. To test this theory, the researchers utilized data from the Whitehall II study (completed mostly by middle-aged office staff in London, England). After initial screening, information from more than 4200 participants (over 75% male) was found to be applicable to the present experiment.

The statistical analysis compared multiple variables. Diet-based inflammation potential was established using the Dietary Inflammatory Index (DII), recurrent depressive symptoms (DepS) were identified using the Center for Epidemiologic Studies Depression Scale and concentrations of inflammatory markers (IL-6 and CRP) were recovered from stored blood samples. Longitudinal data was obtained for a follow-up period of five years. The results showed that recurrent symptoms of depression were associated with higher DII scores, but only for females. Contrary to expectations, chemical inflammation markers were not significantly related to the process.

The presence of a sex-dependent effect was not expected but does compare with some previous findings in the field. However, the authors suggest that judgements be reserved until further studies with more specific objectives are undertaken, as the limitations of this experiment may have been at least partially responsible for the observed differences. Instead, focus should be given to the fact that the findings demonstrate a significant association between diet-based inflammation and recurrent depressive symptoms. A potential application of this result (pending further confirmation) is the use of nutritional plans that were originally designed to lessen dietary inflammation as a treatment (or even preventative measure) for depression.