Chemicals in processed meat snacks, such as salamis and hot dogs, can contribute to mania, an abnormal mood state characterised by hyperactivity, euphoria and insomnia.
The study, published in the journal Molecular Psychiatry, found that people hospitalised 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 researchers from Johns Hopkins University in the US showed that mania-like hyperactivity after just a few weeks on diets with added nitrates.
The 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," said Robert Yolken, from the Johns Hopkins University.
Mania, a state of elevated mood, arousal and energy that lasts weeks to months, is generally seen in people with bipolar disorder, but can also occur in those with schizoaffective disorder.
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Manic states can lead to dangerous risk-taking behaviour and can include delusional thinking, and most of those affected experience multiple hospitalisations in the course of their psychiatric illness.
Researchers collected demographic, health and dietary data on 1,101 individuals aged 18 through 65 with and without psychiatric disorders.
About 55 per cent of the participants were female and 55 per cent were Caucasian, with 36 per cent identifying as African-American.
A study of their records between 2007 and 2017 showed that among people who had been hospitalised for mania, a history of eating cured meat before hospitalisation were about 3.5 times higher than the group of people without a psychiatric disorder.
Cured meats were not associated with a diagnosis of schizoaffective disorder, bipolar disorder in people not hospitalized for mania or in major depressive disorder.
No other foods about which participants were queried had a significant association with any of the disorders, or with mania.
Nitrates have long been used as preservatives in cured meat products and have been previously linked to some cancers and neurodegenerative diseases, so Yolken suspected they may also explain the link to mood states such as mania.
In experiments with rats, researchers analysed the gut bacteria of the animals. They found that rats with nitrate in their diet had different patterns of bacteria living in their intestines than the other rats.
Moreover, the animals had differences in several molecular pathways in the brain that have been previously implicated in bipolar disorder.
While the team also cautions that it's too early to take any clinical messages from the results, and occasional cured meat consumption is unlikely to spur a manic episode in most of the population, Yolken said the findings add to evidence of the multiple factors that contribute to mania and bipolar disorder.
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