People with severe gum disease have been found to have low levels of antioxidant chemicals that may offer natural protection.

Other studies have shown that periodontal disease, in which bacteria attack the teeth and gums, appears to be a genuine threat to general health.

The first thing you should do if you have periodontal disease is stop smoking

Dr Simon Langley-Evans, University of Nottingham

It is not only a prime cause of teeth-loosening, but has been linked to both the onset of diabetes, and a worsening of lung disease.

Studies have even pointed to gum disease as a potential threat to unborn children.

However, research at the School of Dentistry at the University of Birmingham has uncovered clues as to why some patients suffer and some do not.

They closely analysed a type of saliva called gingival crevicular fluid - the small quantity of liquid found between the teeth and gums.

They found that levels of a key antioxidant called glutathione were much higher in patients who had healthy gums.

Patients with severe gum disease had very low levels of the chemical.

In the journal Molecular Pathology, published on Tuesday, the researchers wrote: "Whatever the reason, these observations have important implications for the pathogenesis and treatment of periodontal disease."

Further research, they said, would help determine "new therapeutic strategies".

Measuring disease

Dr Simon Langley-Evans, a lecturer in nutrition at Nottingham University, told BBC News Online that it was hard to tell if low antioxidant levels were a cause of the spread of gum disease - or simply a sign that the body was using up its reserves fighting back.

However, he said that measuring these chemicals could be a reliable predictor of the severity of disease.

He said: "We should be able to predict whether a patient has very bad periodontal disease or a mild case."

He said that hopefully, one day, researchers might find a way to boost antioxidant levels in patients with a treatment or diet advice.

However, his recent research had found that adding vitamin C to the diet appeared to have no effect.

He said: "The first thing you should do if you have periodontal disease is stop smoking.

"Cigarette smoke destroys antioxidants."