Eating processed meat could raise someone's risk of having a manic episode.

A study of more than 1,000 people, including those with psychiatric disorders, found people who had consumed processed meat were three and a half times more likely to have been hospitalised for mania.

Manic episodes, where people become hyperactive, euphoric and cannot sleep, affect one to two in 100 people, including presenter Stephen Fry and Hollywood actress Carrie Fisher.

They are part of bipolar disorder, which used to be called 'manic depression'.

Eating processed meat could raise someone's risk of having a manic episode

Researchers at Johns Hopkins University asked people if they had ever eaten dry, cured meats.

While salami and prosciutto were not linked to mania, cured 'meat sticks' were linked to an increased chance of hospitalisation.

They say nitrates, used as meat preservatives, may affect the brains and gut bacteria of people who eat them. Nitric oxide is found in higher levels within the blood of people with bipolar disorder.

Lead author Dr Robert Yolken, from Johns Hopkins University School of Medicine, said: '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.'

Processed meat is also known to increase people's risk of bowel cancer (stock image)

To test the effects of nitrates, the US researchers added them to the diet of rats, which showed signs of mania after just a few weeks.

In the human study, people were asked if they had eaten meat sticks in the form of turkey and beef jerky, 'meat sticks', prosciutto and salami.

Meat sticks and jerky are popular snacks in the US, and less so in the UK, however nitrates are used here as preservatives for a minority of sausages and may also be in bacon and burgers.

The study, published in the journal Molecular Psychiatry, found nitrates changed the gut bacteria of rats, which may be linked to mental health problems. It follows evidence that giving people with bipolar disorder probiotics, to alter their gut bugs, makes them less likely to be rehospitalised.

Processed meat is also known to increase people's risk of bowel cancer.

Dr Yolken said: 'We looked at a number of different dietary exposures and cured meat really stood out. It wasn't just that people with mania have an abnormal diet.'

Seva Khambadkone, a co-author who worked on the rat experiment, added: 'It's clear that mania is a complex neuropsychiatric state, and that both genetic vulnerabilities and environmental factors are likely involved in the emergence and severity of bipolar disorder and associated manic episodes.

'Our results suggest that nitrated cured meat could be one environmental player in mediating mania.'