Does obesity increase the risk of thrombosis (blood clots)?

Obesity and Blood Clot Risk: A Definitive Link

Yes, obesity significantly increases the risk of blood clots (thrombosis), with higher obesity classes showing the greatest risk. According to the European Society of Cardiology, each kg/m² increase in BMI is associated with a 10% increase in venous thromboembolism (VTE) risk, and severe obesity (BMI >40) increases VTE risk three-fold compared to normal weight 1.

Evidence for Obesity-Thrombosis Link

Venous Thromboembolism (VTE) Risk

• Mendelian randomization studies demonstrate causality between obesity and VTE 1
• Each standard deviation increase in genetically predicted BMI increases VTE odds by 59% (OR 1.59,95% CI 1.20-1.93) 1
• Class 3 obesity (BMI >40) is associated with a three-fold increase in VTE risk (HR 3.4,2.87-4.03) compared to normal weight 1
• Individuals with Class 2 or higher obesity who are over 50 years old have a 6.2-fold increased risk of VTE compared to those with Class 1 obesity or normal weight 1, 2

Surgical Risk

• During surgery, obesity significantly increases thrombosis risk:
  • After orthopedic surgery, Class 2+ obesity doubles pulmonary embolism risk 1
  • In bariatric surgery patients, VTE risk doubles in those with BMI >50 1
  • Across all major surgeries, all obesity classes show higher VTE risk without increased bleeding risk 1

Arterial Thrombosis

• Obesity increases risk of atherothrombosis (arterial blood clots) 1
• For each 5 kg/m² BMI increase above 25, coronary heart disease risk increases four-fold 1

Mechanisms of Thrombosis in Obesity

Several pathophysiological mechanisms explain why obesity increases thrombosis risk:

1. Chronic Inflammation: Obesity creates a proinflammatory state that activates coagulation pathways 3

2. Impaired Fibrinolysis: Obesity impairs the body's ability to break down blood clots 3, 4

3. Adipokine Dysregulation: Abnormal secretion of hormones from fat tissue promotes thrombosis 3, 5

4. Mechanical Effects: Physical effects of body fat limit venous return, promoting stasis 4

5. Prothrombotic State: Obese individuals have higher levels of coagulation factors (including factors VIII and IX) 1, 6

Clinical Implications

Risk Assessment

• Obesity should be considered a significant risk factor when evaluating thrombosis risk 2, 7
• The risk appears dose-dependent - higher BMI classes correlate with greater thrombosis risk 1
• When combined with other risk factors (e.g., oral contraceptives), obesity has synergistic effects, increasing thrombosis risk up to 10-fold in women with BMI >25 who use oral contraceptives 6

Prevention Strategies

• Weight management should be considered a thrombosis prevention strategy 7, 5
• Weight loss reduces concentrations of coagulation factors and plasminogen activator inhibitor-1 toward normal ranges 4
• For obese patients undergoing surgery, consider:
  • Mechanical thromboprophylaxis with compression stockings and/or intermittent pneumatic compression 2
  • Weight-adjusted doses of low molecular weight heparin (LMWH) 2
  • Extended thromboprophylaxis for high-risk patients 2

Conclusion

The evidence clearly demonstrates that obesity significantly increases the risk of both venous and arterial thrombosis through multiple mechanisms. This risk increases with higher obesity classes, with Class 3 obesity (BMI >40) carrying the highest risk. Weight management should be considered an important strategy for reducing thrombosis risk in obese individuals.