Emerging scientific inquiry suggests a potential protective effect of citrus fruit consumption against the onset of depressive disorders, positing that the abundance and metabolic functions of Faecalibacterium prausnitzii, a prevalent gut bacterium, may mediate the impact of citrus fruits and their flavonoid compounds on emotional well-being.
Samuthpongtorn et al. report that citrus intake and its components are prospectively associated with a lower risk of depression and altered abundance of 15 gut microbial species, including enriched Faecalibacterium prausnitzii. Image credit: Hans.
Depression represents a pervasive and incapacitating ailment, affecting a global population exceeding 280 million individuals.
The exact etiologies of depression remain elusive, and therapeutic interventions frequently prove suboptimal.
A considerable proportion, seventy percent, of individuals diagnosed with depression do not experience a favorable response to initial antidepressant treatments, or they encounter unacceptable adverse effects from the prescribed medications.
Dietary patterns present a promising avenue for both the prevention and management of depressive symptoms.
Adherence to a Mediterranean-style diet has been correlated with a nearly 35% reduction in the likelihood of developing depression, and this dietary approach has likewise demonstrated efficacy in ameliorating mood disturbances.
While the specific food constituents contributing to these favorable outcomes are not yet fully understood, citrus fruits, encompassing oranges and grapefruits, have been recently implicated in a decreased risk of depression.
Nevertheless, the underlying biological mechanisms that elucidate the relationship between diet and depression remain subject to further investigation.
In a recent investigation, Dr. Raaj Mehta, affiliated with Harvard Medical School as an instructor in medicine and a practicing physician at Massachusetts General Hospital, along with his research team, conducted an analysis exploring the intricate interplay between citrus consumption, the gut microbiota, and the susceptibility to depression, drawing data from over 32,427 participants.
The researchers prospectively evaluated the long-term dietary intake of citrus fruits in relation to depressive symptomatology and the prevalence of specific gut microbial species. Subsequently, they examined the correlations between these microbial species, their metabolic capabilities, and the incidence of depression.
“I was collaborating with a highly capable postdoctoral researcher named Chatpol Samuthpongtorn, who was thoroughly reviewing the existing literature on depression, seeking an engaging research project,” Dr. Mehta recounted.
“He encountered a particular publication from 2016 that hinted at the potential for citrus to mitigate the risk of depression.”
“This discovery captured our attention, particularly as we had access to an extensive dataset that could be utilized to further explore this finding.”
“This dataset is derived from the Nurses’ Health Study II (NHS2), initiated in 1989 with the primary objective of identifying risk factors for major chronic diseases in women.”
“It encompasses more than 100,000 female participants who, approximately every two years, furnish researchers with comprehensive details concerning their lifestyle habits, dietary intake, medication usage, and overall health status.”
“Consequently, we resolved to leverage this wealth of information to ascertain whether nurses who consumed significant quantities of citrus exhibited reduced rates of future depression compared to their counterparts who did not. And our findings corroborated this hypothesis!”
The findings indicated that the daily consumption of one medium-sized orange could potentially reduce the risk of developing depression by approximately 20%.
“When we examine an individual’s overall intake of fruits or vegetables, or specific fruits like apples or bananas, we do not observe any discernible correlation between their consumption and the risk of depression,” Dr. Mehta commented.
A distinctive aspect of this study involved a subset of participants from the NHS2 who provided multiple fecal samples over the course of a year.
“Utilizing the DNA sequencing data obtained from these fecal samples, we investigated potential links between citrus consumption and particular bacterial species residing within the gut microbiome,” Dr. Mehta stated.
“One specific bacterial species, Faecalibacterium prausnitzii, emerged as particularly noteworthy.”
“Its presence was more pronounced in individuals who reported no depressive symptoms compared to those experiencing depression, and a high intake of citrus was also correlated with elevated levels of Faecalibacterium prausnitzii.”
“Therefore, we hypothesize that this bacterium may serve as a crucial link connecting citrus consumption with positive mental health outcomes.”
“Given that the NHS2 exclusively comprises female participants, we deemed it essential to validate these findings in a study that included men.”
“To achieve this, we turned to a parallel study, known as the Men’s Lifestyle Validation Study, where we also observed an inverse correlation between increasing levels of Faecalibacterium prausnitzii and depression risk scores.”
“This led us to ponder the specific mechanisms by which Faecalibacterium prausnitzii might contribute to improved mood.”
“One plausible explanation, in our estimation, is that these bacteria engage a metabolic pathway identified as the S-adenosyl-L-methionine cycle I pathway, which influences the production of two key neurotransmitters – serotonin and dopamine – synthesized by human cells within the gut.”
“While these neurotransmitters play a role in regulating the digestive process, they also possess the capacity to traverse to the brain, where they exert a mood-elevating effect.”
“It is my hope that our findings will stimulate further research into the intricate relationship between diet and mental well-being.”
“I believe there is an intuitive understanding among the public that the foods we consume have an impact on our emotional state.
“We even have a colloquial term for this phenomenon: comfort foods, which provide transient solace. However, researchers are only beginning to unravel the specific scientific underpinnings.”
A research article detailing these discoveries has been published in the esteemed journal Microbiome.
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C. Samuthpongtorn et al. 2024. F. prausnitzii potentially modulates the association between citrus intake and depression. Microbiome 12, 237; doi: 10.1186/s40168-024-01961-3
