Eating an orange a day may lower a person’s depression risk by 20%, according to a study led by Raaj Mehta, an instructor in medicine at Harvard Medical School. Mehta is also a physician at Massachusetts General Hospital.
Mehta said a postdoctoral student he was working with found a 2016 paper pointing to the possibility that citrus lowers the risk of depression.
“That piqued our interest because we had access to a rich data set that we could use to follow up on this finding,” Mehta said. “It’s called the Nurses’ Health Study II (NHS2), and it began in 1989 with the goal of finding risk factors for major chronic diseases in women. It involves over 100,000 women … So, we decided to leverage these data to look for evidence that nurses who ate a lot of citrus had lower rates of future depression than those who did not. And that’s what we found!”
“We found that eating one medium orange a day may lower the risk of developing depression by about 20%,” Mehta said. “And the effect seems to be specific to citrus.”
Mehta said a subset of participants in the NHS2 gave researchers several samples of their stool over the course of a year. “Using DNA sequencing results from these stool samples, we looked for links between citrus intake and particular species of bacteria in the gut microbiome,” Mehta said. “One species of bacteria stood out. Faecalibacterium prausnitzii was more abundant in people who were not depressed than people who were. Consuming a lot of citrus was also associated with high levels of F. prausnitzii. So, we think this bacterium may link citrus consumption with good mental health.”
Mehta continued: “Because the NHS2 only includes women, we wanted to confirm the findings in a study involving men. So, we turned to a similar study, called the Men’s Lifestyle Validation Study, where we also saw increasing levels of F. prausnitzii were inversely correlated with depression risk scores.”
Mehta said researchers think these bacteria may use a metabolic pathway to influence levels of two neurotransmitters — serotonin and dopamine — produced by human cells in the gut. These neurotransmitters regulate how food passes through the digestive tract, but they can also travel to the brain, where they elevate mood.
“I would love to see a clinical trial done to definitively show that eating citrus can lower the risk of depression, or maybe even alleviate the condition in some cases,” Mehta said. “More broadly, I hope our results inspire other researchers to look into the link between diet and mental health.”
Source: The Harvard Gazette
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