Workplace and Leisure Time Physical Activity: Opposing Relations with Progression of Early Atherosclerosis. The Los Angeles Atherosclerosis Study.
Background. While exercise during leisure is a consistent protective factor for CVD, there is inconsistency across studies concerning the impact of physical activity during work. The current study investigated the relationship between progression of sub-clinical atherosclerosis and physical activity during work and during leisure time. Methods. Participants were from a cohort of 573 randomly sampled utility workers asymptomatic for CVD who were aged 40-60 years at entry. Physical activity during leisure was determined from the number of times per week the subject reported working up a sweat; physical activity during work was ascertained from an NHLBI Physical Activity Index. Sub-clinical atherosclerosis was measured as intima-media thickness (IMT) of the common carotid arteries by high resolution B-mode ultrasound. 36 month change in IMT was measured in microns per year. Results. The mean (±SD) IMT in the sample with complete follow-up (n=447) was 678±106 μm. Those scoring in the highest quintile of workplace activity had significantly more IMT progression compared with those in the lowest quintile (mean±SE = 13.0±1.8 vs 6.9±1.8 μm/yr, respectively; p for trend=0.02 in a model adjusted for age, sex, age-sex interaction, smoking status, alcohol use, use of blood pressure and/or cholesterol lowering medications, BMI, HDL-c, total serum cholesterol, heart rate, systolic blood pressure, and intake of supplemental vitamin C and E). For leisure activity, significantly less IMT progression was found with more activity, but only among those in the highest quintile of activity relative to those in the other 4 quintiles (6.5±1.8 vs 10.9±0.9 μm/yr; p=0.03 in a model adjusted for the same covariates listed above). No significant interaction with sex was detected. Workplace activity was strongly correlated with workplace psychological stress (ρ=0.56), which was previously shown to be a risk factor for IMT in this cohort. Conclusions. These findings suggest that protective effects of physical activity may be blocked or counteracted when activity is performed in a psychologically stressful context.