Semiparametric regression of the illness-death model with interval censored disease incidence time: An application to the ACLS data

To investigate the effect of fitness on cardiovascular disease and all-cause mortality using the Aerobics Center Longitudinal Study, we develop a semiparametric illness-death model account for intermittent observations of the cardiovascular disease incidence time and the right censored data of all-cause mortality. The main challenge in estimation is to handle the intermittent observations (interval censoring) of cardiovascular disease incidence time and we develop a semiparametric estimation method based on the expectation-maximization algorithm for a Markov illness-death regression model. The variance of the parameters is estimated using profile likelihood methods. The proposed method is evaluated using extensive simulation studies and illustrated with an application to the Aerobics Center Longitudinal Study data.

The Association of Cardiorespiratory Fitness and Ideal Cardiovascular Health in the Aerobics Center Longitudinal Study

Background: This study examined the cross-sectional and longitudinal associations of cardiorespiratory fitness (CRF) and ideal cardiovascular health (CVH). Methods: CRF and the 7 CVH components were measured in 11,590 (8865 males; 2725 females) adults at baseline and in 2532 (2160 males; 372 females) adults with at least one follow-up examination from the Aerobics Center Longitudinal Study. Ideal CVH score was calculated as a composite of 7 measures, each scored 0 to 2. CVH groups were based on participant point score: ≤7 (poor), 8 to 11 (intermediate), and 12 to 14 (ideal). Analyses included general linear, logistic regression, and linear mixed models. Results: At baseline, participants in the high CRF category had 21% and 45% higher mean CVH scores than those in the moderate and poor CRF categories (P < .001). The adjusted odds (95% confidence interval) of being in the poor CVH group at baseline were 4.9 (4.4–5.4) and 16.9 (14.3–19.9) times greater for individuals with moderate and low CRF, respectively, compared with those with high CRF (P < .001). Longitudinal analysis found that for every 1-minute increase in treadmill time, CVH score increased by 0.23 units (P < .001) independent of age, sex, exam number, and exam year. Conclusions: Higher CRF is associated with better CVH profiles, and improving CRF over time is independently associated with greater improvements in CVH.

Two Physical Activity Measures: Paffenbarger Physical Activity Questionnaire Versus Aerobics Center Longitudinal Study as Predictors of Adult-Onset Type 2 Diabetes in a Follow-Up Study

Purpose: To compare 2 self-report methods of measuring weekly minutes of physical activity based on the Aerobics Center Longitudinal Study (ACLS) questionnaire and question 6 of the Paffenbarger Physical Activity Questionnaire (PPAQ) to determine the better predictor of adult-onset type 2 diabetes mellitus (T2DM). Design: An observational, prospective study. Setting: Survey data from the Adventist Health Study-2 (AHS-2) collected between 2002 and 2006 (baseline) and the Psychosocial Manifestations of Religion Sub-Study (PsyMRS), an AHS-2 subset collected 1 to 4 years later. Patients: Nine thousand eight hundred seventy-three male and female participants aged 23 to 106 years (mean, 63 years). Three hundred eighty participants reported adult-onset T2DM at follow-up. Measures: Question 6 from the PPAQ and a question adopted from the ACLS were assessed at baseline. Incident diabetes was defined as participants who reported receiving treatment for adult-onset T2DM in the last 12 months in the PsyMRS and not at baseline. Analysis: Multivariate logistic regression analyses controlled for age, gender, ethnicity, education, body mass index (BMI), diet, and sedentary activity. Each exposure variable was compared to nonexercisers. Results: The PPAQ (odds ratio [OR]: 0.998; 95% confidence interval [CI]: 0.997-1.000) and the ACLS (OR: 0.999; 95% CI: 0.998-1.001) exhibited similar likelihood of predicting incident adult-onset T2DM in a healthy, mixed-gender population when controlling for several confounders. Conclusions: The demonstrative nomenclature of the PPAQ may be more effectual in capturing physically active individuals than the ACLS notwithstanding generalizability and response bias limitations.

Abstract 37: The Association of Cardiorespiratory Fitness and Ideal Cardiovascular Health in the Aerobics Center Longitudinal Study

Purpose: To examine the cross-sectional association between cardiorespiratory fitness (CRF) and ideal cardiovascular health (CVH) in middle-aged adults. Methods: The association between CRF and ideal CVH score was examined in 11,590 adults (8,865 men, 2,725 women) from the Aerobics Center Longitudinal Study. CRF was measured as duration in minutes from a maximal treadmill test. The AHA’s ideal CVH score was calculated on a 14 point scale using data on smoking status, BMI, physical activity (MET-min/wk), healthy diet, total cholesterol, blood pressure, and fasting plasma glucose recorded between 1987 and 1999. Participants were grouped into categories of inadequate (0-4), average (5-9), and optimum (10-14) based on their CVH score. Three CRF groups were created from age- and sex-specific quintiles based on the previously established cutpoints of treadmill time: low, moderate, and high CRF. We used general linear and logistic regression models adjusted for age, sex, and year of examination to evaluate the association of CRF with ideal CVH score. Results: The mean CVH score for men was 8.4 ± 2.2 and 9.7 ± 2.0 for women. Approximately 33% of men and 57% of women had optimum CVH, while only a small proportion of participants had inadequate CVH (5.1% M, 1.4% F). Treadmill time was moderately correlated (p<0.0001) with CVH score in both men (r=0.56) and women (r=0.50). CRF explained 16% and sex 18% of the variance in CVH score (both p<0.0001). Our adjusted model found that participants in the optimum CVH category had 20% and 43% higher CRF levels than those in the average and inadequate CVH groups (p<0.0001), respectively ( Figure 1 ). The adjusted odds (95% CI) of having optimum CVH were 14.0 (11.0-17.8) and 3.1 (2.4-4.0) times greater for high CRF and moderate CRF, respectively, compared to low CRF (p<0.0001). Discussion: Higher levels of cardiorespiratory fitness are associated with better cardiovascular health profiles in both men and women. Thus, improving fitness represents a strategy to improve cardiovascular and public health.