Marie Knoll

Date of Award

Summer 2020

Document Type

Open Access Thesis


Epidemiology and Biostatistics

First Advisor

Susan Steck


Depression is a chronic disease which inflicts functional and emotional impairment that has been a growing issue in the United States (US). Depression is the most prevalent mental disorder in the US and is the leading cause of disability in the world. By 2030, It is projected that major depressive disorder will be the second largest contributor to global burden of disease. Causes of depression are still largely unknown and treatments are often expensive, time consuming, and only available to certain populations. Treatment often requires a combination of medicines and therapy to be effective. In recent years, the gut microbiome has emerged as an important contributor to a variety of cognitive functions. It has been demonstrated in many studies that a healthy gut supports normal central nervous system function through the gut-brain axis. Clinical studies have reported that the gut microbiota of depressed patients is significantly different from that of healthy controls while some research has found that both the microbiota diversity and richness was lower in depressed patients in comparison to healthy controls. The microbiome is an emerging field of research with many of its mechanisms and potential still unknown. The current study examined the associations between urinary enterolignans (enterolactone and enterodiol) as a marker for gut microbiome diversity and depressive symptoms in human subjects using the National Health and Nutrition Examination Survey. The Patient Health Questionnaire-9 was used for determining depression status of participants. We categorized urinary enterolignans into quartiles using the distribution among the healthy, non-depressed participants and examined associations with depressive symptoms using survey logistic regression. The study found that participants in the highest enterolactone quartile were less likely to be experiencing depressive symptoms compared to those in the lowest quartile. While associations between depressive symptoms and urinary enterodiol were generally inverse, the effect estimates were weaker and none of the trend tests were statistically significant. The results provide support for the hypothesis that gut microbiome diversity is inversely related to depressive symptoms. These findings may lend support to intervention studies aimed at altering the gut microbiota composition for improving psychological symptoms.

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