An apple a day may keep the doctor away, but new research shows it takes an orange a day to keep the blues away. Scientists at Harvard University found eating an orange a day may reduce the risk of depression by 20 percent.
Eating an orange has many benefits, but these new findings elevate this fruit to a new category for its preventative powers.
Researchers found that orange consumption was able to stimulate the growth of a certain type of gut bacteria thought to elevate mood. The bacterial strain Faecalibacterium prausnitzii (F. prausnitzii), which was found in higher quantities in those who ate citrus, is associated with the production of the neurotransmitters serotonin and dopamine.
The positive benefits regarding the risk of depression were specific to citrus. Researchers looked at total fruit and vegetable consumption and found no correlation with reduced risk and even isolated apples and bananas without any link.
The research team used data from more than 100,000 women in the Nurses' Health Study II (NSH2), which extensively detailed the lifestyle, diet, medication use, and health of nurses over a long period of time. They also used data from the Men's Lifestyle Validation Study.
"One unique part of the study is that a subset of participants in the NHS2 gave researchers several samples of their stool over the course of a year," said Raaj Mehta from Harvard Medical School. "Using DNA sequencing results from these stool samples, we looked for links between citrus intake and particular species of bacteria in the gut microbiome.
"One species of bacteria stood out—F. prausnitzii was more abundant in people who were not depressed than people who were, and 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 said he things the gut bacteria use a specific metabolic pathway known as the S-adenosyl-L-methionine cycle I pathway in the production of serotonin and dopamine in the gut. Those neurotransmitters regulate how food passes through the digestive tract, but they can also travel to the brain where they can positively influence mood.
Researchers said it was hard to compare the results they found to the effectiveness of traditional antidepressants, such as SSRIs. That's because the focus of the study was to look at depression prevention rather than treating symptoms after someone is already experiencing depression. They said more work needs to be done to see if there is a way to incorporate citrus into a depression management strategy.