There is no singular cause for mental illness. Any number of things – our genes, the environment and even social customs – play a role in determining whether a person's mental health will deteriorate to the point of being diagnosed as an illness. But researchers from Johns Hopkins have stumbled upon a possible trigger for manic episodes they did not expect to find: Jerky.
Since 2001, researchers have been tracking the health of patients who were readily admitted to one of several hospitals in the Baltimore, Maryland area. The study is still ongoing. In 2007, they started asking patients about their diets. Robert Yolken, a neurovirologist at the Johns Hopkins University School of Medicine, wanted to use this data to investigate a possible association between foodborne infections and mental illness.
But when he and his team reviewed the anonymous data of more than 1,000 volunteers (a cohort that included the psychiatric patients and a control group of people recruited from nearby health centers and colleges without diagnosis of a mental illness), a strange pattern began They appear among people diagnosed with mania, a state of hyper-excitement, arousal, and delusions, followed by periods of severe depression in people with bipolar disorder. Compared to the control group, people with a manic episode reported eating more cured meat. Overall, they found that people who were recently able to eat cured meat were hospitalized three times more frequently for mania, even though they were adjusted to factors such as age or socioeconomic status. The same pattern could not be seen in any other kind of food.
"We did not look for that," Yolken told Gizmodo. "It came as something of an unexpected result."
Hoping to confirm that it was the odd food, Yolken turned to other researchers and began experimenting with rats. Because jerky and similar products are hardened with nitrate salts, they hypothesized that nitrates could be the main driver of a mania effect.
They fed rats bought at the store jerky everyday (the equivalent of one human snack a day) and compared them to a control group. The jerked rats showed symptoms of hyperactivity and poor sleep within two weeks, whereas the control group did not. Next, they fed specially prepared dried meat without nitrate to another group of rats, finding that these rats did not develop symptoms. And finally, they gave rats a typical rat food loaded with nitrates and found the same pattern.
The results of the study were published Wednesday in Molecular Psychiatry.
"It's definitely fascinating and probably better than many other studies that rely only on mice and rats," said Emeran Mayer, a gastroenterologist at the University of California who was not involved in the research, to Gizmodo.
"The rat experiments are pretty convincing … but in humans it can be a lot more complicated," said Mayer, who studied and wrote about how gut microbiota can affect the brain. "Nutritional feedback and questionnaires are pretty notoriously unreliable, which is probably a weak point of study."
As for the jerky mania, Yolken suggests that it is the microbial environment or the microbiome of the gut. In a healthy person, the gut and brain "talk" regularly about hormone and nerve signals to keep the body regulated, the so-called gut-brain axis. In recent years, researchers have found that our gut microbiota is essential to keep these radio waves free. But if the gut microbiota is unbalanced (for example, through dietary changes or antibiotics), it could trigger a chain of events that damage both the brain and the gut, often through chronic inflammation. This inflammation could then make people more susceptible to the development of mental illness or worsening of their symptoms.
And indeed, when Yolken's team looked at the entrails of nitrate-fed rats, they found significant changes in gut microbiota in the form of an increase in certain types of bacteria compared to normal rats. These particular bacteria have been previously associated with behavioral and cognitive changes in animals. There was also evidence of tiny molecular changes in the brain associated with mania in these rats, although Yolken pointed out that the results can not prove that the intestinal changes led to changes in the brain. Nor can they even prove that nitrates are responsible for similar changes in humans.
Yolken himself points out that the study, especially the results in humans, is not definitive. No other study, as far as he knows, has linked nitrates to mental illness (although it has been linked to diseases such as cancer when found in drinking water as an impurity). And much more research on animals and humans is needed before such a connection can be confirmed. Even if nutrition plays a role in the risk of mental illness, this is just one of many factors that interact in complex ways that we do not fully understand.
That's self-evident, says Mayer, because nitrates, whether in hot dogs or beef jerky, are an omnipresent part of the North American diet. But not everyone who loves hot dogs develops mania. Even if the connection is real, it's just part of the puzzle.
"Microbes do not just cause anxiety, depression or autism in humans," said Mayer. "They only affect people who have a genetic or environmental predisposition to disease, and that's just one of many."
Attempting to repair the microbiome may not be helpful in treating all types of mental illness. Yolken and his team recently published a double-blind study that showed that mania patients taking probiotic pills with a mixture of "good" bacteria to stabilize the microbiome in addition to standard treatment had a lower risk of being admitted to their hospital for another episode will be six months. But he has also published studies showing that probiotics had no effect on reducing the symptoms of people with schizophrenia.
Nevertheless, Yolken hopes that his study will raise more attention (and funding) for the study of the connection between the gut, diet and mind.
"We do not want to frighten people about their diet, but this is definitely a promising area that needs further investigation and study," Yolken said.
"I do not suggest interventions," he added.