Urban air pollution, mostly from vehicles, is associated with an increased risk of dementia, according to research published Wednesday.

The link remained even after heavy drinking, smoking and other well-established risk factors for dementia were ruled out, the researchers reported in the medical journal BMJ Open.

Worldwide, about 7 percent of people over 65 suffer from Alzheimer's or some form of dementia, a percentage that rises to 40 percent above the age of 85.