A team of researchers led by Dr. Raaj Mehta, a faculty member at Harvard Medical School and a physician at Massachusetts General Hospital, has analyzed the connection between citrus consumption, the gut microbiome, and the likelihood of depression. The scientists discovered that the gut bacteria Faecalibacterium prausnitzii may modulate the effects of citrus fruits and their flavonoids on mood.
Depression and Nutrition
More than 280 million people worldwide suffer from depression. The exact causes of this widespread condition remain unknown, and its treatment is often ineffective. Medical professionals report that initial treatment with antidepressants fails to help 70 percent of patients with depression. Moreover, these medications frequently lead to serious side effects.
Researchers have long noted that diet may be a promising means of preventing and treating depression. For instance, the Mediterranean diet is associated with nearly a 35 percent reduction in the risk of developing depression. However, the mechanisms explaining the link between nutrition and depression remain unclear.
What Scientists Discovered
Recently, Dr. Mehta’s team found a connection between citrus consumption, particularly oranges and grapefruits, and a lower risk of developing depression.
“I was working with a wonderful postdoctoral fellow named Chatpol Samutpongthorn, who was reviewing the literature on depression in search of an interesting project to tackle. He came across a 2016 article suggesting that citrus fruits might reduce the risk of depression,” Dr. Mehta explained.
With access to a large dataset, the researchers set out to explore this theory in greater depth, as reported by Sci.news. The team utilized data from the Nurses’ Health Study (NHS) II, which began in 1989 and aimed to identify risk factors for major chronic diseases in women.
Over 100,000 women participated in the study, providing detailed information about their lifestyle, diet, medication use, and health status every two years. Thus, Dr. Mehta’s team decided to “use this data to find evidence that nurses who consumed a lot of citrus had lower rates of future depression compared to those who did not.”
And here’s what the scientists found: consuming one medium orange a day reduced the risk of developing depression by approximately 20 percent.
“When we look at the overall fruit and vegetable consumption among people or individual fruits like apples or bananas, we don’t see any connection between that and the risk of depression,” Dr. Mehta noted.
Using DNA sequencing results from stool samples, the researchers sought to find a link between citrus consumption and specific types of bacteria in the gut microbiome. This connection was demonstrated by one type of bacteria—Faecalibacterium prausnitzii.
“In individuals who do not suffer from depression, there were higher levels of this bacteria compared to those who do, and high citrus consumption was also associated with elevated levels of Faecalibacterium prausnitzii,” the lead researcher pointed out. According to him, this particular bacterium may connect citrus consumption with good mental health.
Since the study only included women, the scientists needed to confirm their findings in a male cohort as well. They examined results from a similar study—the “Men’s Lifestyle Validation Study”—and ultimately found that increased levels of Faecalibacterium prausnitzii inversely affected depression risk.
“Then the question arose: how does Faecalibacterium prausnitzii help people feel better? We think one answer may be that these bacteria utilize a metabolic pathway known as the S-adenosyl-L-methionine cycle to influence the levels of two neurotransmitters—serotonin and dopamine—that are produced by human gut cells,” Dr. Mehta explained.
He added, “These neurotransmitters regulate the passage of food through the digestive tract but can also travel to the brain, where they elevate mood.”
The scientist hopes these results will inspire other researchers to explore the connection between diet and mental health. “I think people intuitively understand that the food we eat affects our mood. We even have a term for it: comfort food, which is food that makes us feel better.”
The study’s findings were published in the journal Microbiome.