Background Physical activity (PA) has previously been suggested to attenuate the risk of atrial fibrillation (AF) conferred by excess body weight and weight gain. We prospectively examined the relationship between body size, weight change and level of PA in a biracial cohort of middle-aged men and women. Methods and Results Baseline characteristics on risk factor levels were obtained on 14,219 participants from the Atherosclerosis Risk in Communities Study. AF incidence was ascertained from 1987–2009. Adjusted Cox proportional hazards models were utilized to estimate the associations between body mass index (BMI), waist circumference (WC), relative weight change, and PA level with incident AF. During follow-up, there were 1775 cases of incident AF. BMI and WC were positively associated with AF, as was weight loss/gain of >5% initial body weight. An ideal level of PA had a small protective effect on AF risk and partially attenuated the risk of AF associated with excess weight in men but not women: compared with men with a normal BMI, the risk of AF in obese men with an ideal, intermediate and poor level of PA at baseline was increased by 37%, 129% and 156% (Pinteraction=0.04). During follow-up, PA did not modify the association between weight gain and risk of AF. Conclusions Obesity and extreme weight change are risk factors for incident AF whereas being physically active is associated with a small reduction in risk. In men only, being physically active offset some, but not all, of the risk incurred with excess body weight.

Background Aspirin for the primary prevention of coronary heart disease (CHD) is only recommended for individuals at high risk for CHD although the majority of CHD events occur in individuals who are low to intermediate risk. Methods and Results To estimate the potential of coronary artery calcium (CAC) scoring to guide aspirin use for primary prevention of CHD, we studied 4229 participants from the Multi-Ethnic Study of Atherosclerosis (MESA) who were not on aspirin at baseline and were free of diabetes. Using data from median 7.6-year follow-up, five-year number-needed-to-treat (NNT5) estimations were calculated by applying an 18% relative CHD reduction to the observed event rates. This was contrasted to 5-year number-needed-to-harm (NNH5) estimations based on the risk of major bleeding reported in an aspirin meta-analysis. Results were stratified by a 10% 10-year CHD Framingham Risk Score (FRS). Individuals with CAC ≥ 100 had an estimated net benefit with aspirin regardless of their traditional risk status (estimated NNT5 of 173 for individuals <10% FRS and 92 for individuals ≥ 10% FRS, estimated NNH5 of 442 for a major bleed). Conversely, individuals with zero CAC had unfavorable estimations (estimated NNT5 of 2,036 for individuals <10% FRS and 808 for individuals ≥ 10% FRS, estimated NNH5 of 442 for a major bleed). Gender specific and age-stratified analyses showed similar results. Conclusion For the primary prevention of CHD, MESA participants with CAC ≥ 100 had favorable risk/benefit estimations for aspirin use while participants with zero CAC were estimated to receive net harm from aspirin.