Headlines declaring a link between the nitrates in cured meat and bipolar mania – a serious mood disorder characterized by irrational euphoria, erratic behavior, hyperactivity, and insomnia – have been splashed across the news following the publication of a study led by the Johns Hopkins University School of Medicine.

But can beef jerky, Slim Jims, pepperoni, and the like really induce a psychiatric disorder? It’s simply too soon to say at this point – but the new research raises some interesting questions for further exploration. Let’s look at what they found.

Writing in the journal Molecular Psychiatry, the team of investigators reports that they first noticed a relationship between nitrate consumption and mania by accident. Between 2007 and 2017, researchers at the nearby Sheppard Pratt Health System asked 758 willing psychiatric patients to fill out comprehensive lifestyle questionnaires as part of a separate project. As Live Science notes, the question about eating cured meats was only added to the survey as filler. Yet when they analyzed the decades-worth of answers for any notable trends, the authors unexpectedly revealed that people who had been hospitalized for an episode of mania were 3.5 times more likely to have a history of eating nitrated cured meat compared with healthy control subjects (n=343) who filled out the same questionnaire, after adjusting for other potentially impacting factors.

Previous health studies have linked dietary nitrates and nitrites, chemicals added to processed food to prevent bacterial growth and prolong shelf-life, to both cancer and neurodegenerative diseases.

Interestingly, cured meat was not associated with other disorders or bipolar disorder in people not hospitalized for mania, and eating other types of meat products or fish was not linked to any psychiatric outcomes.

A follow-up investigation that asked 42 new manic patients and 35 additional controls more detailed questions about their diets replicated the results: consuming ‘meat sticks’, beef jerky, or turkey jerky was associated with 3.5 to 5.15 times greater likelihood of having bipolar mania.  

Intrigued by this pattern, Yolken and his colleagues sought to substantiate the correlations with experiments designed to test cause and effect. Because a study on humans would be highly unethical, they turned to lab rats. And because there is no known diagnosis of bipolar mania in rodents, the team had to assess whether intake of cured meat led to the closest cognitive parallel – hyperactivity.

In the first experiment, two groups of healthy rats were fed standard rat chow, but those in one group also received a piece of store-bought beef jerky every other day. After just two weeks, the jerky group displayed hyperactivity and abnormal sleep schedules.

The subsequent experiment duplicated this set-up but added a third group that was fed a specially prepared nitrate-free jerky. Finally, the third test involved two groups of rats given either standard chow or chow with added nitrate. In both these experiments, the rats not consuming nitrates behaved normally, yet those who were showed similar sleep disturbances and hyperactivity.

Yolken emphasizes that the level of nitrates the rats were receiving corresponds to about the equivalent of an adult eating one jerky stick or hot dog a day.

"It's clear that mania is a complex neuropsychiatric state, and that both genetic vulnerabilities and environmental factors are likely involved in the emergence and severity of bipolar disorder and associated manic episodes," said first author Dr Seva Khambadkone. "Our results suggest that nitrated cured meat could be one environmental player in mediating mania."

Though the altered rat behavior is insufficient proof of the manic effect nitrates have in people, the authors have already identified a potential mechanism. When assessing physiological changes in the rats, they noted that those in the nitrate groups had a different composition of bacteria living in their intestines compared with the control rats, and a different study by Yolken’s lab suggests that bipolar patients taking probiotics may experience fewer manic episodes.

"There's growing evidence that germs in the intestines can influence the brain," says Yolken. "And this work on nitrates opens the door for future studies on how that may be happening."