MESA is a multicenter cohort study conducted at 6 US field centers in Baltimore, Chicago, Forsyth County, North Carolina, Los Angeles, New York, and St. Paul, Minnesota. Between July 2000 and September 2002, 6814 persons between the ages of 45-84 were recruited into the study. Participants identified themselves as White, Black, Hispanic, or Chinese at the time of enrollment. Persons with a history of cardiovascular disease defined as physician-diagnosed MI, angina, stroke or transient ischemic attack, heart failure, resuscitated cardiac arrest, or having undergone procedures related to CVD (coronary artery bypass graft, angioplasty, valve replacement, pacemaker or defibrillator implantation, or any surgery on the heart or arteries) were excluded. The study was approved by the institutional review boards of each site, and all participants gave written informed consent. Details of the design of MESA have been reported previously.10
Data from the MESA baseline examination (2000-2002) and from a follow-up examination conducted approximately 5 years later (2005-2007) were used in these analyses. Of the 6814 participants at baseline (2000-2002) 6452 participants were included in these analyses (). We excluded individuals who were subsequently found to have cardiovascular disease at baseline, users of anticoagulant therapy (since aspirin use for primary prevention in this population is not indicated), and participants with missing data for any variable. Follow-up analyses (2005-2007) were based on 5181 participants (). Exclusion criteria included individuals who died or were lost to follow-up between baseline and 2005-2007, those found to have cardiovascular events during follow-up, users of anticoagulant therapy, and individuals with missing data for any variable.
Flow chart of the study. CVD = Cardiovascular Disease; MESA = Multi-Ethnic Study of Atherosclerosis.
Cardiovascular events during follow-up were defined as MI, resuscitated cardiac arrest, definite or probable angina (if followed by revascularization), stroke, or death due to stroke, CHD, or any other atherosclerotic or CVD. Cardiovascular events were initially identified by interviewers who contacted each participant or a family member by telephone to inquire about interim hospital admissions, outpatient diagnoses of CVD, and deaths. Self-reported diagnoses were verified by 2 physicians and an analysis of medical records. A more detailed description of the MESA follow-up methods is available at www.mesa-nhlbi.org
Gender, race/ethnicity (based on questions modeled on the Year 2000 Census), income, and education were assessed at baseline. Information regarding age and insurance status was obtained at each examination using standardized questionnaires. Age was categorized into 10-year age groups. Individuals with any type of insurance were labeled “insured”; those without any type of insurance were labeled “uninsured”. Information regarding income was collected at baseline and at follow-up in 2004-2005. Income was sorted into 4 categories ranging from < $12,000 to ≥ $50,000, in concordance with categories established in a previous study.8
Response categories for highest level of education completed were collapsed into 3 categories: less than high school, high school (or equivalent), or more than high school. The 2003 American Diabetes Association criteria were employed such that diabetes mellitus was defined as a fasting glucose ≥ 126 mg/dL and/or the self-reported use of insulin and/or oral hypoglycemic agents.11
We calculated the 10-year CHD risk for each subject using the National Cholesterol Education Program Framingham risk score, which estimates the risk for hard CHD (nonfatal MI and death from CHD).12
The Framingham risk score has been validated for use in multiple ethnicities.13
The only exception was for adults with diabetes, for whom the 10-year CHD risk was assumed to be > 20% making them high risk by definition.2
Information regarding age, gender, current cigarette use (defined as cigarette use within the past 30 days), and use of antihypertensive medications were acquired using standardized questionnaires. Systolic blood pressure was obtained by taking the average of 2 Dinamap Pro 1000 automated oscillometric sphygmomanometer (Critikon) measurements, in mmHg. Fasting total and high-density lipoprotein cholesterol were directly measured by a central laboratory. Since the Framingham risk score was designed for ages < 80, we assigned those with ages 80-85 a risk equivalent to age 79. For purposes of analysis, the 10-year CHD risk was stratified into 3 mutually exclusive categories based on the USPSTF and AHA guidelines from 2002: low risk (< 6%), increased risk (6% to 9.9%), and high risk (≥ 10%).1-2
Information regarding regular aspirin use was obtained via standardized questionnaires at each examination. Regular aspirin use was defined as taking aspirin at least 3 days per week. This definition was intended to capture participants who use aspirin every day or every other day, since studies have shown both to be effective for preventing CHD.4-7
Aspirin use was presumed to be for cardioprotection and no information regarding aspirin allergies or analgesic use of aspirin was available.
Chi-square tests were used to test for differences in the prevalence of aspirin use across categories of participant characteristics. Logistic regression models were used to assess the association between aspirin use and each participant characteristic. Models were constructed using a forced entry method whereby all potential confounders were forced into the model. Independent variables were examined for multicollinearity and excluded from analysis if their tolerance value was < 0.10. Insurance status was excluded from the models given concerns for overadjustment and collinearity with income and education. Results are reported as odds ratios with 95% confidence intervals. Analyses were completed separately for baseline examination data from 2000-2002 and follow-up data from 2005-2007. Results were contrasted. All analyses were conducted with PASW 17.0.