In a large population-based study that included 23,201 men and women between 40 and 79 years of age who participated in the EPIC-Norfolk study, Myint et al. examined the relationship between usual physical activity and fibrinogen concentrations. Participants were classified into 4 groups of physical activity levels (active, moderately active, moderately inactive, and inactive) based on a questionnaire that took into account leisure-time and work-related physical activity. After adjusting for age, smoking, body mass index (BMI), prevalent illness, occupational social class, and alcohol consumption, inactive men had fibrinogen levels of 2.97±0.02 g/L (mean±SEM) and active men had fibrinogen levels of 2.82±0.02 g/L (p<0.0001 across the 4 categories). In women, the respective fibrinogen values for inactive and active women were 3.03±0.01 g/L and 2.95±0.02 g/L (p<0.0001). The difference between fibrinogen values across physical activity levels seemed to be more pronounced in older participants, participants with an elevated BMI, and participants who had never smoked. As fibrinogen levels were inversely associated with increasing physical activity levels, the authors concluded that fibrinogen might contribute to a mechanism that could explain the decreased cardiovascular disease risk associated with physical activity.