They believe that low cholesterol may stimulate impulsive and extreme behaviour that may result in people dying from harming themselves or becoming involved in road traffic accidents.

However, they found no link between cholesterol levels and people who specifically intended to kill themselves.

A team from St Vincent's Hospital, Dublin, compared 100 patients admitted to the hospital with self-inflicted injuries, including drug overdoses, with psychiatric patients and patients not suffering from any mental health problems.

The patients were rated on their level of depression, impulsivity and suicidal intent.

It was found that cholesterol levels in the patients who had deliberately harmed themselves were significantly lower than the other patients.

Cholesterol levels were also low in all patients who were rated as being impulsive.

Impulsive people

Lead researcher Dr Malcolm Garland said people who deliberately harmed themselves often had no intention of killing themselves.

He said: "Very often it is an impulsive act, a cry for help, especially after a few drinks, or when there are interpersonal problems.

"Impulsive people are often very immature personalities who tend to act in an off the cuff way."

Dr Garland said cholesterol was linked to the transmission of serotonin, an important brain chemical responsible for the control of mood and emotion.

"Cholesterol is an extremely important component of the brain, especially of the nerve cell membranes," he said.

"It makes sense that if you have got a high or low level of cholestrol that might influence the way the nerve cells work."