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Cured meats such as salami or jerky may worsen the symptoms of some people with mental illness, researchers reported Wednesday.
They found that people hospitalized for mania were three times as likely to say they had eaten cured meats compared with people who did not have a psychiatric disorder.
The researchers are quick to say that they have not proven that eating cured meats causes mental illness, or even that a little jerky hurts someone with, say, bipolar disease. But they ran some other experiments suggesting that the nitrates in processed meats might affect someone’s mental state.
“We are not trying to scare people,” said Dr. Robert Yolken of the Johns Hopkins University School of Medicine, who led the study team.
“We found that a history of eating nitrated dry cured meat but not other meat or fish products was strongly and independently associated with current mania,” Yolken and colleagues wrote in their report, published in the journal Molecular Psychiatry.
“The cured meat products were generally in the form of meat sticks, beef jerky and turkey jerky, which are cured meat products generally prepared with added nitrates.”
The team was actually looking for a possible infectious-disease link with mania, which is a common symptom of some mental health conditions, such as bipolar disorder, and which includes excited and sometimes delusional behavior, as well as sleeplessness and irritability.
They interviewed about 1,100 people, including patients with psychiatric disorders treated at the Sheppard Pratt Health System in Baltimore from 2007 to 2017.
They were asked about what they had eaten because Yolken had a theory that viruses or other microorganisms from food might affect symptoms.
“We looked at a number of different dietary exposures and cured meat really stood out,” Yolken told NBC News.
Yolken said they took into account the possibility that people with mental illness might eat differently. “It wasn’t just that people with mania have an abnormal diet,” he said.
And he has a theory for what might be going on. “We think the key is probably inflammation,” Yolken said.
Nitrates in food are linked with cancer, which is in turn linked with inflammation. And Yolken said other studies have shown that people who have manic episodes show signs of inflammation in their bodies.
“We do want to raise the question of whether inflammation processes are important in psychiatric disorders,” he said.
But how to test the potential effects of nitrates or other food ingredients in people? “It is very hard to show cause and effect in diet in humans,” Yolken said.
So the researchers tried testing rats, feeding them beef jerky loaded with nitrates every other day.
They also fed rats nitrate-free jerky.
The rats that ate the nitrates seemed more hyperactive, the team reported. “The animals don’t get mania in the sense that people do,” Yolken said. But some aspects of rat biology and human biology are similar, and it seemed that the nitrates altered the microbiome — the gut bacteria — of the rats.
Yolken and other researchers have shown that altering the microbiome can affect the symptoms of psychiatric disorders, including schizophrenia. It’s not entirely clear why, but more and more research is showing that the bacteria that live in and on our bodies affect health in profound ways.
Yolken believes that the balance of bacteria may play a role in inflammation, which may in turn affect the symptoms of mania in people who are genetically predisposed to psychiatric illness.
“I think that for people with mania, and perhaps other disorders as well, there might be environmental triggers that you can control,” he said.
Outside experts noted that the work is very preliminary.
“We’d need much more evidence of a link before making any recommendations to patients or the public in relation to the risk of eating cured meat and developing mania," said Dr. Anthony Cleare, a psychiatry professor at King's College London who was not involved in the study.