A study of the dietary habits of more than 1,000 people with and without psychiatric disorders has found a link between eating nitrated cured meats such as beef jerky and meat sticks, and episodes of mania, a serious neuropsychological disorder that is one of the defining characteristics of bipolar disorder (BPD).
The team said further research is needed to understand the mechanism by which nitrates increases the risk of mania, but tests on rats showed that rodents which ate nitrate-added jerky displayed irregular sleeping patterns and hyperactivity compared with those which did not.
Mania is an abnormal mood state often characterised by hyperactivity, euphoria and insomnia.
"There's growing evidence that germs in the intestines can influence the brain", Yolken said.
Researchers collected demographic, health and dietary data on 1,101 individuals aged 18 through 65 with and without psychiatric disorders.
Dr Yolken said: 'We looked at a number of different dietary exposures and cured meat really stood out.
(The survey did not collect information on how recently the people had consumed the foods, or how much they had eaten, but Yolken says most people answered based on their recent diets.) They were asked about cured meats, as well as about raw and uncooked meats.
Research led by Johns Hopkins University on patients accepting administer to hyper manifestations discovered they were more than three times more inclined to have at any point eaten prepared meat items than patients being dealt with for other mental conditions, for example, schizophrenia.
The study can't prove that nitrates in foods actually cause mania, as only an association was seen. No other foods had a significant association with any of the disorders.
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"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".
Experiments in rats by the researchers from Johns Hopkins University in the USA showed that mania-like hyperactivity after just a few weeks on diets with added nitrates.
The study, published in the journal Molecular Psychiatry, found nitrates changed the gut bacteria of rats, which may be linked to mental health problems.
So the researchers tried testing rats, feeding them beef jerky loaded with nitrates every other day.
"In patients at risk for manic episodes, it is possible that dietary exposures interact with existing genetic vulnerabilities and other environmental and social risk factors in the emergence and severity of the illness", the Hopkins researchers said.
Nitrates used to cure the meats are to blame, according to experts at Johns Hopkins University School of Medicine in Baltimore.
The human study wasn't powered to investigate cause-and-effect, so the team next investigated the potential effects of nitrate-cured meats on the behaviors of healthy rats. "Our results suggest that nitrated cured meat could be one environmental player in mediating mania".
Nitrates have always been used as preservatives in cured meat products and have been previously linked to some cancers and neurodegenerative diseases. It follows evidence that giving people with bipolar disorder probiotics, to alter their gut bugs, makes them less likely to be rehospitalised.