An analysis of more than 1,000 people with and without psychiatric disorders has shown that nitrates—chemicals used to cure meats such as beef jerky, salami, hot dogs, and other processed meat snacks—may contribute to mania, an abnormal mood state. Mania is characterized by hyperactivity, euphoria, and insomnia.

The findings of the Johns Hopkins Medicine study, which was not designed to determine cause and effect, were published July 18 in Molecular Psychiatry. Specifically, it found that people hospitalized for an episode of mania had more than three times the odds of having ever eaten nitrate-cured meats than people without a history of a serious psychiatric disorder.

Experiments in rats by the same researchers showed mania-like hyperactivity after just a few weeks on diets with added nitrates.

While a number of genetic and other risk factors have been linked to the manic episodes that characterize bipolar disorder and may occur in other psychiatric conditions, those factors have been unable to explain the cause of these mental illnesses, and researchers are increasingly looking for environmental factors, such as diet, that may play a role.

The researchers say that their new study adds to evidence that certain diets and potentially the amounts and types of bacteria in the gut may contribute to mania and other disorders that affect the brain.

“Future work on this association could lead to dietary interventions to help reduce the risk of manic episodes in those who have bipolar disorder or who are otherwise vulnerable to mania,” says lead author Robert Yolken, MD, the Theodore and Vada Stanley Distinguished Professor of Neurovirology in Pediatrics at the Johns Hopkins University School of Medicine.