Published in the Journal of Thrombosis and Thrombolysis, new research with a follow-up of 27 years has found an association between high levels of physical activity (PA) and an elevated risk of venous thromboembolism (VTE).
The research, led by Per Wändell (Karolinska Institutet, Huddinge, Sweden) and colleagues, was drawn from the Uppsala Longitudinal Study of Adult Men (ULSAM). Their team followed a cohort of 2,294 patients in Uppsala, Sweden who were initially examined at age 50, with data on their PA levels collected over four follow-up periods at ages 60, 70, and 77. After a median follow-up time of 33 years, 186 cases of first-time VTE were recorded, with a total of 68,263 person-years at risk.
Wändell and his team defined activity levels by grade 1–4:
- Mainly sedentary behaviour (reading, watching television)
- Walking or cycling (for pleasure walking, cycling)
- Recreational sports or heavy gardening for at least 3 hours every week
- Regularly engage in hard physical training (hard training or participation in competitive sports, regularly and several times a week
Results from the study showed that men with the highest levels of physical activity—defined by the authors as engaging in regular strenuous exercise—had a more than doubled risk of developing VTE (adjusted hazard ratio [HR] of 2.22; 95% confidence interval [CI] 1.05–4.67) compared to those who reported the lowest PA levels. The findings suggest that, while moderate exercise has well-documented health benefits, there may be a point at which intense physical activity could increase VTE risk.
Using Cox regression analysis, Wändell et al adjusted for cardiovascular risk factors such as blood pressure, cholesterol levels, body mass index, diabetes, and smoking. Despite these adjustments, the elevated risk remained significant in the highest PA group.
In their subsequent commentary, the authors write that VTE is the third most common type of cardiovascular disease in Sweden, with a marked increased risk with age. Although low levels of exercise are associated with higher cardiovascular disease and VTE risk, there have been documented cases of cardiovascular events occurring after strenuous exercise, such as sudden cardiac death in long-distance running.
In men, the increased risk of VTE is may be due to that exercise sessions including long and vigorous extreme exertion is associated with an imbalance between pro-thrombotic and fibrinolytic factors, thus causing hypercoagulability together with a weakened fibrinolysis. Other possible explanations include a more pronounced effect on platelet function during strenuous exercise, or dehydration which increases blood viscosity, therefore causing a higher clotting probability, the authors explain.
The study authors acknowledge limitations of their study, including the relatively small sample size and the use of self-reported physical activity data, which may have led to misclassification of activity levels. They state that their variables do not provide absolute predictors of VTE due to the potential for unaccounted factors, yet they contend that their lengthy follow-up period and careful patient examination bolster their results.
The researchers emphasise that clinicians should be aware of the possible risk of VTE in patients engaging in high levels of strenuous exercise on a regular basis, as to not delay diagnosis and treatment. Further, for individuals taking part in marathons or ultra competitions, they add that spreading awareness of the early signs of VTE is crucial.
