Can citrus prevent depression? What a Harvard study finds about oranges, grapefruit and your brain

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Turns out, an orange a day might do more than boost vitamin C levels. It may also help lower the risk of depression.

Scientists at Harvard Medical School and Massachusetts General Hospital have identified a possible link between regular citrus consumption and a reduced risk of depression. According to their study, published in November in the journal Microbiome, participants who reported eating more than one serving of citrus per day had a 22% lower risk of developing depression, compared to those who consumed less than one serving per week.

The researchers’ theorize this effect could be thanks to citrus’s ability to promote the growth of F. prausnitzii, a type of gut microbe that may be linked to feel-good chemicals like serotonin and dopamine. The study found more F. prausnitzii in people who reported eating more citrus.

There’s growing interest in better understanding how food affects mood, and how changes in the gut microbiome — the mix of microbes living in our digestive tracts — influence mental health. The study authors say their work makes a compelling case for taking a closer look at how changes in diet and the gut microbiome could play a role in preventing depression, which affects approximately 280 million people worldwide.

I spoke with Dr. Raaj Mehta, a gastroenterologist and lead researcher of the study, about his team’s exploration into the gut-brain connection. He told me after a 2016 paper suggested a potential link between citrus and depression, the team decided to take a deeper dive.

Here are some highlights from our conversation, edited for length and clarity:

Were you surprised by these findings? As a gastroenterologist, when you’re evaluating patients how often is mental health brought up?

"I was surprised by citrus having a strong association with depression resistance, but I wasn't surprised to see more evidence of a gut-brain connection. In clinic, many patients with gastrointestinal symptoms — like constipation or diarrhea — see their symptoms worsen with stress. After almost a decade of seeing this, it's no surprise there's a connection between the gut and brain. Additionally, it's not just the brain that affects the gut; there are studies showing that Parkinson’s disease (which is not a mental health condition) could potentially start in the gut. Some of the earliest signs of Parkinson's are constipation, even before tremors appear, so attention to how the gut affects the brain is increasing."

How is F. prausnitzii linked with citrus? How far does this connection go?

"We found that citrus was linked to higher levels of F. prausnitzii in the gut. This is interesting because F. prausnitzii is associated with healthier states, with lower levels in patients with inflammatory bowel disease or obesity. It suggested we might be heading in the right direction. More specifically, F. prausnitzii may produce chemicals that affect serotonin and dopamine synthesis, and the second half of our paper was trying to answer the why question. It's sort of an unusual thing to say that something you eat can travel all the way up to your brain and influence your mood. It happens every day, like I just ate some animal crackers, and I feel a little bit happier, but it's a little bit hard to explain biologically. So that was our goal, to try to provide at least a hypothesis for how this might occur, because it's a long distance from your large or small intestine to your brain."

What kind of citrus is most effective? Can I drink citrus juice or or even have a citrus tablet?

"Our study primarily focused on oranges and grapefruits, fruit and juice both. But there's no reason that it couldn't apply to other types of citrus. Your question about a tablet with a citrus extract, I think is interesting. We had some exploratory analyses that suggested there might be specific components in citrus that could potentially explain our results. But in the end, I think you probably would need to do some more research to identify exactly what should go in a tablet."

Can you compare the effect of common depression medications known as SSRI’s to the effect of daily citrus intake?

"It’s tough to compare since we were focused on risk reduction for future depression while SSRIs treat depression that’s already happening. The next step could be a diet-plus-medication study, where a dietary component complements standard treatment. We're starting to see this in other fields, and I think it would be an interesting direction."

What are the challenges in conducting studies like yours, especially when looking at diet and mental health?

"It’s hard to get funding for something like that. If you're a drug company, you can't really put a price tag on an orange and sell it with your SSRI. Similarly, it's a difficult funding environment right now for investigators. Also, dietary studies are especially difficult. You can’t just have people eat oranges three meals a day for six months. You have to account for other foods they eat, which adds complexity."

How important is the gut microbiome to mental health? Is it overlooked by current treatments?

"The microbiome is the forgotten organ inside of our guts. It can modulate some of the things we eat, good or bad, and affect how we feel. One thing that's really interesting about the microbiome, as an organ inside of us, is that it is modifiable. So unlike your genes, which are fixed more or less, the genes in bacteria that do all sorts of things can be changed. Hopefully people will start to exploit in the next two to three decades.

"It’s not as simple as saying 'take this probiotic and feel better,' we don’t have the evidence yet. But if more people talk about it, someone might do a major study and unlock new knowledge."

How long before researchers can confidently say citrus lowers depression risk?

"It’s probably too early to say 'eat an orange a day to keep the blues away,' but at the same time it’s not a dangerous message to send. Eating healthy can improve mood and there’s tons of evidence that fruits and vegetables can reduce risk of cancer, diabetes, high blood pressure, obesity, etc. I’d say, if you don’t have adverse reactions or aversions to citrus, might as well try occasionally in moderation."

Correction: An earlier version of this story gave inaccurate figures for the number of servings that lowered study participants' risk of depression, as well as by how much. Participants who consumed one serving of citrus daily were found to have a 22% lower risk of depression compared to those who ate less than a serving a week. The story also misspelled Mehta's first name. The post has been updated. We regret the errors.