The goal of this randomized, double-blind, crossover trial is to test the hypothesis that a longer-term indoor HEPA filtration intervention can improve cardiometabolic profiles by reducing indoor PM2.5 exposures in at-risk individuals.

This randomized, double-blind, crossover trial will recruit 52 non-diabetic adults and will investigate potential benefits of HEPA air purifiers on improving cardiometabolic profiles. Participants will be contacted and recruited to the study based on inclusion and exclusion criteria. After consenting, participants will be block randomized to HEPA and control groups for 6-month interventions by sex. After 6-month wash-out period, participants will be switched to the other arm of the intervention. During the trial, project specialists will complete a series of home visits before and after each intervention session to set up air purifiers and indoor and outdoor air pollution monitors, as well as conduct interview to collect questionnaire data, measure body weight and blood pressure, and collect biospecimen. In aim 1, the researcher will assess the effect of a 6-month residential HEPA intervention on changes of type 2 diabetes-related metabolic outcomes in 52 adults. In aim 2, the researchers will examine the association between reduction in indoor PM2.5 exposure brought by the intervention and changes in metabolic outcomes adjusting for ambient PM2.5 exposure. In aim 3, the researchers will explore major pathophysiologic changes pertinent to the cardio-metabolic profile of type 2 diabetes relevance in response to the intervention and changes in PM2.5 exposure.

Inclusion Criteria:

• Age between 65 and 84 years old;
• Nonsmoker for at least 1 year;
• History of BMI ≥ 25 kg/m2 in the past based on EMR information;
• Either an English or Spanish speaker;
• Live in the Los Angeles County.

Exclusion Criteria:

• History of diabetes (both type 1 and type 2) or degenerative disease of the nervous system (Alzheimer's disease or dementia);
• Currently have active cancer treatment;
• The residential house has already had HEPA filters;
• Participants will move out of the current house in the next 2 years;
• Participants will spend more than one month living outside the primary home;
• Have any health conditions that prohibit collecting health and covariate data and biospecimen;
• The residential houses are not feasible for setting up air purifiers and air pollutants monitors;
• Have high blood glucose from finger stick test (> 200 mg/dL).

A sham filter will be used in the control, to replace HEPA filter in the intervention group. Participants and investigators will be blinded to the intervention type, only specific investigator who will prepare air filter for intervention will be unblinded for the real air filter type.