Jobs encompassing prolonged sitting in cramped positions and risk of venous thromboembolism: cohort study

OBJECTIVES: There is mounting evidence that prolonged cramped sitting in connection with long-lasting air travel increases the risk of deep vein thrombosis of the legs and pulmonary embolism, i.e. venous thromboembolism (VTE). Prolonged cramped sitting may occur even in various jobs unrelated to air travel, and, theoretically, be associated with an increased risk of VTE. The issue is unsettled. DESIGN: A dynamic cohort study (open for both entry and departure) in Danish national registers 1997–2006. PARTICIPANTS: 20–59-year-old manual workers. The cohort consisted of an exposed group with job functions basically characterised as sedentary (n = 105,564) and a control group with more dynamic work (n = 283,966). SETTING: Denmark. MAIN OUTCOME MEASURES: Deaths and hospital contacts due to pulmonary embolism and deep vein thrombosis. RESULTS: Compared with occupations characterized by dynamic physical activity, the group encompassing those who would potentially be exposed to prolonged sitting in ergonomically adverse positions, had a significantly higher risk of pulmonary embolism (n = 77, relative risk 1.28; 95% CI 0.97–1.67, P = 0.04 in one-sided test). With respect to deep vein thrombosis they had a slightly but not significantly higher risk (n = 256, relative risk 1.09; 95% CI 0.94–1.26, P = 0.12). CONCLUSION: Despite the crude method used allowing for no control of individual risk factors, occupations encompassing longer and shorter periods of sitting in potentially adverse ergonomic positions, i.e. cramped sitting, had a higher risk of VTE, than a socioeconomically comparable group with more dynamic physical work demands.