Background: There is epidemiological evidence or link ambient air pollution exposure to the incidence of dementia.

Aims or hypotheses: It is hypothesized that reduction in indoor pollutants from air purification improves endothelial function and carotid intima thickness in older diabetic people with cognitive impairment.

Subjects and method: People with clinically diagnosis mild cognitive impairment or early dementia will be recruited. After obtaining written consent, the subjects will be assessed cognitive function and arterial health. After baseline measurements, the subjects are randomly assigned to have either filter or no filter installed in the air purifier. The air purifier will be placed in living room of the household of the subject for one year. At one year, the measurements will be repeated.

Statistical analysis: Intention to treat analysis will be adopted.

Inclusion Criteria:

• Diabetic people
• Mild cognitive impairment or early dementia

Exclusion Criteria:

• Current smoker
• The presence of a smoker in the household
• The absence of a reliable family caregiver
• The lack of mental capacity to give informed consent