Covariates

Demographic characteristics, including age, gender, race, education level, marital status and family income, were collected. Participants were categorised as non-Hispanic white, non-Hispanic black, Mexican American and other ethnicity. Educational level was analysed as a two-level categorical variable: less than high school and completion of or more than high school. Marital status (unmarried and other, married/with a partner) was analysed as a two-level categorical variable. The indicator for family income—the poverty income ratio—was categorised as below poverty (<1.00) and at or above poverty (≥1.00). Lifestyle factors included cigarette smoking and alcohol consumption. Former/current smoker was defined as participants who currently smoked and had smoked at least 100 cigarettes in their lifetime. Current drinker was defined as participants who currently drank.

General health was assessed by body mass index (BMI), physical activity, C reactive protein (CRP) and comorbidities. Height and weight were used to calculate BMI (kg/m²). Obesity was defined as BMI >30 kg/m². The 2008 Physical Activity Guideline for Americans suggests at least 2.5 hours of moderate-intensity or 75 min of vigorous-intensity aerobic physical activity per week or an equivalent combination of moderate-intensity and vigorous-intensity aerobic activity for health benefits. We categorised participants into two groups based on whether the 2008 Physical Activity Guideline was met or not. CRP was categorised as two groups (high CRP level: CRP ≥1 mg/dL or not).

Clinical comorbidities included diabetes mellitus, hypertension, hyperlipidaemia, chronic kidney disease (CKD) and self-reported history of cardiovascular disease (CVD). Diabetes mellitus was defined as serum glycosylated haemoglobin >6.5%,²⁹ the use of insulin or diabetic tablets or self-reported history of diabetes mellitus. Hypertension was defined as systolic blood pressure of ≥140 mm Hg or diastolic blood pressure ≥90 mm Hg, the use of antihypertensive agents or self-reported history of hypertension. Hyperlipidaemia was based on total cholesterol ≥240 mg/dL, the use of lipid-lowering medications or self-reported history of high cholesterol. CKD was defined as estimated glomerular filtration rate <60 mL/min/1.73 m². Self-reported history of CVD was based on previous diagnosis of congestive heart failure, coronary heart disease, angina, heart attack or stroke.