People with gingivitis (gum disease) have worse mental function than their peers whose gums are in better shape, a new analysis of US data shows.

The findings raise the possibility that system-wide inflammation due to gum disease could have harmful effects on brain function. However, because the study only looked at a single time point it could not gauge whether or not there is a causal relationship between oral health and cognitive performance.

Older people with bad teeth are more likely to have dementia and cognitive impairment, Dr. Robert Stewart of the Institute of Psychiatry in London and colleagues note, but it isn't known whether a similar relationship is present in younger people, and whether factors that can affect both dental health and mental function such as heart disease, high blood pressure or smoking may be involved.

To investigate, the researchers analyzed data from the Third National Health and Nutrition Examination Survey III. Stewart and his team looked at 5,138 adults aged 20 to 59 who had completed two tests of cognitive function, and another 1,555 adults aged 70 and older given a different mental function test.

After the researchers adjusted for the effects of age, they found associations between worse performance on any of the three cognitive tests and bleeding gums, loss of periodontal attachment (meaning the ligament that attaches teeth to bone), and tooth loss.

Oral health could influence cognitive function through several mechanisms, the researchers note; for example, periodontal disease can cause inflammation throughout the body, a risk factor for loss of mental function, while poor oral health can lead to a worse diet, which could affect mental function by leading to nutritional deficiency.

The fact that the association between poor oral health and worse mental function was not influenced by age suggests that "later life associations do not arise purely because of adverse effects of dementia on oral health care," the researchers conclude.