Consuming citrus might decrease depression likelihood

Recent discoveries add another perspective to “gut instincts.”

Consuming one orange daily could reduce an individual’s depression risk by 20 percent, according to a research spearheaded by Raaj Mehta, who is a medical instructor at Harvard Medical School and a physician at Massachusetts General Hospital. This could be attributed to citrus promoting the growth of Faecalibacterium prausnitzii (F. prausnitzii), a bacterium present in the human gastrointestinal tract, which in turn influences the synthesis of neurotransmitters serotonin and dopamine—two biochemical agents recognized for enhancing mood.

In this refined dialogue with the Gazette, Mehta elaborates on crucial insights from the research.

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What motivated this investigation?

I was collaborating with an excellent postdoctoral researcher named Chatpol Samuthpongtorn, who was perusing literature on depression, searching for a compelling project. He stumbled upon this single article from 2016 that suggested the potential that citrus diminishes the risk of depression.

This ignited our curiosity since we possessed access to an extensive data set that we could utilize to explore this discovery further. It’s called the Nurses’ Health Study II (NHS2), and it commenced in 1989 with the aim of identifying risk factors for significant chronic ailments among women. It includes more than 100,000 women, who provide detailed data regarding their lifestyle, dietary choices, medication usage, and overall health approximately every two years. Thus, we resolved to utilize this information to investigate evidence that nurses who consumed substantial amounts of citrus exhibited lower future depression rates in comparison to those who did not. And that’s precisely what we observed!

What level of impact does this have? How does it compare to standard antidepressants?

Our findings indicate that consuming one average orange daily may diminish the likelihood of developing depression by around 20 percent. Moreover, this effect seems to be particular to citrus. In assessing total fruit or vegetable intake, or looking at other specific fruits like apples or bananas, there is no observable relationship between consumption and depression risk.

It’s challenging to juxtapose the efficacy of citrus with conventional antidepressants, like selective serotonin reuptake inhibitors, given that we are discussing preventing depression, whereas those medications are typically employed to treat depression after it has already manifested. In the future, it is possible that incorporating citrus into one’s diet could serve as a component of a strategy for managing depression alongside these conventional pharmaceuticals. However, further research is essential before we can reach such conclusions.

Can you guide me through the reasoning? How precisely do you believe that consuming oranges decreases the risk of depression?

An interesting aspect of our research is that a subgroup of participants in the NHS2 provided us with multiple stool samples over a year. Using DNA sequencing from these stool samples, we investigated connections between citrus consumption and specific bacterial species in the gut microbiome. One bacterial species stood out—F. prausnitzii was found to be more prevalent in individuals who were not depressed compared to those who were, and there was a notable association between high citrus consumption and elevated F. prausnitzii levels. Therefore, we suspect that this bacterium could link citrus intake with positive mental health.

Given that the NHS2 exclusively includes women, we aimed to confirm these findings in a male-oriented study. Consequently, we consulted a similar study known as the Men’s Lifestyle Validation Study, where we also observed that higher levels of F. prausnitzii correlated negatively with depression risk factors.

This led us to question, how does F. prausnitzii contribute to improved well-being? One possible explanation is that these bacteria utilize a metabolic pathway known as the S-adenosyl-L-methionine cycle I pathway to influence the levels of the two neurotransmitters— serotonin and dopamine—produced by human gut cells. These neurotransmitters not only regulate food transit through the digestive system but can also be transported to the brain, where they enhance mood.

Were the outcomes unexpected for you?

Yes and no. There is a substantial amount of evidence now supporting a robust link between the gut and the brain, so I was not taken aback by further findings. Simultaneously, I had not previously associated citrus with cognitive functions until these results emerged. It’s common to hear that fish is “brain food,” yet seldom do people label oranges the same way. Likewise, while F. prausnitzii has been associated with positive health outcomes in various ways, such as reducing the risk of inflammatory bowel disease, I was unaware of its connection to mental health.

What’s on the horizon for this research?

I would dearly like to see a clinical trial conducted to unequivocally demonstrate that consuming citrus can reduce the risk of depression or potentially alleviate the condition in certain instances. There is a significant unmet demand for depression treatments, and integrating citrus into one’s routine has minimal side effects, making it essential to assess the efficacy of this straightforward intervention.

On a broader scale, I aspire for our findings to motivate other scholars to explore the connection between dietary habits and mental health. There’s a general understanding that what we consume influences our emotional states. We often refer to it as comfort foods, which provide temporary relief. Yet, researchers are only beginning to grasp the nuances involved.

The Nurses’ Health Study II received funding from the National Cancer Institute, National Institutes of Health.