The rise in obesity may be going hand-in-hand with increases in severe gum disease, US research suggests.
Obesity is linked to a range of health problems
As many as 40% of adults worldwide have periodontal disease, and tests on mice hint that obesity makes us vulnerable to the bacteria which cause it.
Boston University scientists reported in the journal Proceedings of the National Academy of Sciences that fat mice had a "blunted" immune system.
This may mean obese humans are more at risk from all bacterial infections.
Links between gum disease and other more serious illnesses continue to emerge.
There have even been suggestions of a relationship between gum disease and heart disease risk.
However, the immune changes which might be responsible for this remain poorly understood.
The Boston University study looked in more detail at levels of important immune system chemicals produced by normal, lean mice, and their obese counterparts, when confronted with the P. gingivalis bug that causes periodontal illness.
Both types of mouse had bacteria-infused material wrapped around their gums to see if the disease took hold.
Tests revealed that the obese mice had higher levels of P. gingivalis in their mouths, and were suffering more bone loss around their teeth, one of the most common side-effects of the infection.
In addition, the obese mice had lower levels of certain immune system chemicals normally released by the body to help fight infection.
The researchers wrote: "These data indicate that obesity interferes with the ability of the immune system to appropriately respond to P. gingivalis infection.
"The importance of the current findings is underscored by the facts that millions of people worldwide are affected by this infection every year and the universal prevalence of obesity has reached epidemic proportions."
They said that while their experiments suggested that obesity made the body more vulnerable to gum disease bacteria, it was possible that this "blunting" of the immune system might mean it was more vulnerable to other bacterial attacks.
Dr John Taylor, a senior lecturer in molecular immunology at Newcastle University's School of Dental Sciences, said that his own work was beginning to show strong connections between periodontal disease and type II diabetes, an illness which can arise in obese patients.
He said: "We found that periodontal disease was often of the more aggressive form in patients with diabetes.
"It is possible that obesity may be compromising the immune response, leading to increased susceptibility to periodontal disease."