Gum disease causes bad breath and bleeding gums and if left untreated, cavities, receding gums and tooth loss occur as bacteria or plaque settles between teeth and under the gum line.

Researchers from Imperial College London have found that gum disease is linked to a higher chance of lung, kidney, pancreatic and blood cancers.

The research team who examined the health records of 50,000 men, say an immune system weakness may cause both illnesses and may be a marker of a susceptible immune system or might directly affect cancer risk.

This latest research suggests that, even in those who have never smoked, the presence of gum disease means a bigger risk of cancer.

The majority of people are said to suffer from some sort of gum disease at some time usually caused by a persistent bacterial infection, and the problem is more common in people who smoke.

The study involved questionnaires and health information provided by American men from 1986 onwards which were then analysed and it was found that those with a history of gum disease had a 14% higher chance of cancer compared with those with no history of gum disease.

The men were asked about health and lifestyle, including any gum disease with bone loss and tooth loss in the previous two years, as well as smoking history and diet.

A third of an increase in the risk of lung cancer was seen, almost a 50% rise in the chance of kidney cancer, and a similar rise in pancreatic cancer, while blood cell cancers such as leukaemia rose by 30% among men with gum disease.

The study showed that while there was no rise in lung cancer among those with gum disease who had never smoked, there was a slightly higher increase in the overall risk of any cancer, and a similar rise in the rate of blood cancers.

There are a range of theories as to why the presence of gum disease might be linked to other illnesses - people with gum infections have been found to have chemical signs that the inflammation there may be mirrored in other parts of the body and there have also been suggestions that bacteria linked to gum disease could cause problems elsewhere in the body.

Dr. Dominique Michaud, the lead researcher says that the increase in blood cancers points to an immune system link and suggests that the persistent presence of gum disease might be a sign of weakness in the immune system which could also allow cancer to develop.

On the other hand the researchers say it is also possible that long-lasting gum disease could trigger changes in the immune response which enable cancers to flourish, or that the bacteria from the gum could be directly causing the cancer in the tissues of mouth or throat when swallowed.

While the researchers do not suggest that those with gum disease seek medical help dental experts say the research stresses the need for regular check-ups.

They say while they are trained to spot cancers in the mouth, they were increasingly aware of the implications of gum disease for overall health, and would refer patients to doctors where they were suspicious of serious gum disease in otherwise healthy patients.

Dr. Michaud says that gum disease can be treated and prevented and people need to be encouraged to regularly visit their dentist.

The research is published in Lancet Oncology.