A new study linking a history of mania (commonly associated with bipolar disorder) with certain types of cured meat has gotten a lot of press recently. Because, well, obviously that's a lot to take in.
Startling headlines like "Hot dogs and other cured meats may cause mania, new study finds" and "Can jerky affect mental illness? Study suggests it can," are definitely enough to make you click when you see it in your news feed. And even if you don't read through the articles, the headline alone can be enough to make you give hot dogs a skeptical side eye this weekend.
While we don't often cover single studies, this one piqued our curiosity enough to warrant a deeper dive. So, here's what you need to know about the study before you swear off jerky for good.
The study, published last month in the journal Molecular Psychiatry, analyzed data for more than 1,000 people, both with and without psychiatric disorders.
Specifically, 371 participants had schizophrenia, 217 had mania, 91 had bipolar depression, 79 had major depression, and 343 were control participants who did not have any psychiatric illnesses. The researchers gave participants a survey asking them if they had ever eaten several types of foods, including processed meats (e.g. beef jerky, salami, or prosciutto). They did not ask when, how often, or in what amount participants ate those foods.
Of the participants with mania, 184 of them (87.8 percent) said they had eaten dried cured meat, study co-author Robert H. Yolken, M.D., professor of pediatrics at Johns Hopkins University School of Medicine, tells SELF. And, of the control participants without a psychiatric disorder, 215 of them (62.7 percent) said they had eaten dried cured meat. Taking this, along with other demographic factors (such as gender, age, and cigarette smoking), into account, the researchers concluded that people who had been hospitalized for an episode of mania were more than three times more likely to have ever eaten dry cured meats containing nitrates than people without a history of a serious psychiatric disorder.
But the majority of participants in the study—whether they had a history of mania or not—had eaten processed meats at some point, which makes sense (it's pretty delicious). So, clearly, simply eating processed meat at any point in your life isn't a guarantee that you're going to develop a psychiatric disorder.
After identifying this association between the consumption of cured meats and experiencing mania, the researchers examined the effects of nitrate-prepared meats on rats.
One group of rats was fed regular rat food, and another was fed both regular rat food and "a piece of store-bought, nitrate-prepared beef jerky every other day." The researchers found that within two weeks, the beef jerky-eating group of rats displayed irregular sleeping patterns and hyperactivity. In another experiment, rats that ate nitrate-free beef showed normal activity levels.
The study authors conclude that, “while further investigations are warranted, individuals at risk for mania may consider limiting ingestion of added dietary nitrates.”
The proposed relationship between processed meats and mania in humans is that nitrates affect the microbes in our intestines, known collectively as the gut microbiome.
Nitrate (sodium nitrate) is a type of salt that has been used for thousands of years to preserve meat. Nitrate has been approved by the FDA and the USDA for use in foods, and levels of nitrates in meat products are carefully controlled and monitored. According to the CDC, high levels of nitrates have been associated with heart issues, reproductive issues, cancer, and acute methemoglobinemia, a serious blood disorder. Nitrates are also commonly cited as a possible migraine trigger.
What we eat can change the composition of bacteria in the gastrointestinal tract, Neil Puri, M.D., psychiatrist and assistant professor in the Menninger Department of Psychiatry at Baylor College of Medicine, tells SELF. Certain bacteria may multiply in the presence of certain foods or chemicals, while others may not survive as well. In many cases, these bacteria aren't harmful—they play a role in digestion and the immune system, for instance. And a growing amount of research suggests some gut bacteria may also have an impact on mental health, although we don't know exactly how that might work.
“In this study, rats that were given nitrates had increases in certain bacteria (Lachnospiraceae and Erysipelotrichales) in their GI tracts,” Dr. Puri explains. “An increased presence of these bacteria has been linked to neuropsychiatric disturbances in experimental animals. It is theorized, therefore, that these bacteria may make compounds that impact the neuropsychiatric functioning of the brain.”
Processed meats (and beef jerky in particular) are clearly getting bad press in the wake of this study, but lots of other foods contain nitrates, including most vegetables. In fact, previous research suggests that the majority of the nitrates we consume come from vegetables.
Even though the researchers found an association between cured meat and mania, there are several important limitations to consider.
For instance, the study authors are quick to point out that they didn’t evaluate veggie-based nitrates in their studies. In the animal studies specifically, it seems like something else may be contributing to the hyperactivity effects.
“While the rats consuming a beef-based diet with added sodium nitrate exhibited increased mania-like behavior compared to rats consuming a beef-based diet without sodium nitrate, these changes did not appear to be as severe as those resulting from the consumption of nitrate-processed cured meat itself,” study co-author Wayne W. Campbell, Ph.D., professor of nutrition science at Purdue University, told SELF in a statement. ”Additional studies would be required to determine whether high-nitrate vegetables or other nitrate containing foods could have similar effects compared to nitrate-prepared processed meat.”
Interestingly, although the researchers could statistically link the consumption of cured meats with mania, they were unable to find any link between nitrates and schizoaffective disorder, bipolar disorder ("in people not hospitalized for mania"), or major depressive disorder. No other foods, processed or unprocessed, "had significant association with any of the disorders, or with mania," the authors write.
They also weren’t able to determine the amount of cured meat you’d have to eat to be at a higher risk for mania because the information provided by the study participants didn't include how often they ate cured meat or how the consumption of cured meat related to the time frame of their hospitalization for mania.
Other limitations of the study include the small number of subjects in the animal experiments and the fact that participants were asked to remember what they ate, Dr. Puri says. “There could be many confounding variables in this study, and further studies in animal and humans would need to be done to make a clear link.”
Also, obviously, using rats to examine something as complex and nuanced as mania has its strengths and weaknesses.
In humans, a manic episode is defined as an “extreme mood” characterized by symptoms like being abnormally upbeat, jumpy or wired, or having an exaggerated sense of well-being and self-confidence commonly associated with bipolar and schizoaffective disorders.
But researchers can’t exactly give rats a survey about their mood or behavior changes. “We can’t say that rats are ‘manic’,” study co-author Kellie Tamashiro, Ph.D., associate professor of psychiatry and behavioral sciences at Johns Hopkins School of Medicine, tells SELF. “[But] what we can do is test for behavioral correlates of mania, what we refer to as ‘mania-like behavior.’”
One behavioral test in this study focused on the rats’ activity levels over the course of one day. Across different experiments, rats exposed to nitrate-prepared beef displayed hyperactivity. Those rats also showed hyperactivity during the light cycle period, when rats are generally at a state of rest, which suggested sleep disturbances—another common symptom of mania in humans.
Again, this definitely isn’t clinical mania as it’s defined in humans. But, by allowing researchers to examine behaviors commonly associated with mania, rodent studies offer an opportunity to look at complicated elements of psychiatric illness in a more controlled environment, Tamashiro explains.
Limitations aside, Puri recognizes that the study adds to what we already know to be important: “A healthy diet with an emphasis on fruits, vegetables, and minimally processed foods” is important for physical and mental health.
So, yes, what you eat is a crucial factor for your health. But the role that nitrates (or meat products containing them) specifically play isn’t clear yet—especially when it comes to mental health issues.
“I have not seen mental health patients affected by cured meats,” Dr. Puri says. “However, I have seen people feel mentally much better when they eat a healthier diet.”