This article on Epainassist.com has been reviewed by a medical professional, as well as checked for facts, to assure the readers the best possible accuracy.

We follow a strict editorial policy and we have a zero-tolerance policy regarding any level of plagiarism. Our articles are resourced from reputable online pages. This article may contains scientific references. The numbers in the parentheses (1, 2, 3) are clickable links to peer-reviewed scientific papers.

The feedback link “Was this Article Helpful” on this page can be used to report content that is not accurate, up-to-date or questionable in any manner.

This article does not provide medical advice.


5 Surprising Causes of Blood Clots

No one ever thinks that they will develop a blood clot suddenly. You can go through your entire life without having any such problem or even knowing someone else who developed a blood clot suddenly. The clotting of blood can be a life saver when bleeding needs to be stopped. However, blood clots can also develop when they are not needed. This can prove to be dangerous and cause a stroke, heart attack, or some other serious medical problem. Here are some of the surprising causes of blood clots.

Surprising Causes of Blood Clots

Many people often say that sitting for an extended period of time can make you more susceptible to developing a blood clot deep within the veins of your body, a condition known as deep vein thrombosis (DVT). Surgery is known to be one of the most commonly known risk factors for deep vein thrombosis, and it typically affects the thigh or the lower leg.(1, 2)

While some of the causes of why such blood clots develop are known, there are many other risks that remain unknown or not as well known. At the same time, there is very little awareness of blood clots and their potentially fatal consequences that may take place. The results of blood clots, also known as venous thromboembolism, can include life-threatening blockages of blood in the lungs. Knowing the surprising causes of blood clots can help you be aware, make healthy choices, and also reduce your risk of developing a dangerous blood clot.

  1. Staying in the Hospital

    One of the most common risk factors for developing a blood clot is a stay in the hospital, with or without surgery. This is considered to be a risk factor because you have to keep lying down in bed for prolonged periods of time. According to reports from the National Blood Clot Alliance, being stuck in a wheelchair or bed for extended periods of time when you have to stay in the hospital is one of the leading risk factors for developing fatal blood clots.(3, 4)

    According to estimates by the Centers for Disease Control and Prevention, one in ten hospital deaths is caused by blood clots in the lungs.(5) Furthermore, almost half of all blood clots are known to occur during a hospital stay or within three months of leaving the hospital or having surgery. Any type of major surgery that involves the pelvis, hips, abdomen, or legs increases the risk of developing blood clots since the large veins may get injured during the surgery. Before surgery you should talk to your doctor as you may need to be put on a blood-thinning medication that will reduce the chances of a clot forming. And after the surgery, it is in your best interest to get up and get moving as soon as you feel you are able to.

    If you are ever hospitalized, you should make it a point to ask your doctor about some strategies to decrease the risk of developing blood clots. This may include using sequential compression equipment or wearing elastic compression stockings. Sequential compression devices work by squeezing your muscles so that the blood keeps circulating in the legs. If you have ever stayed in a hospital, you would have seen that the staff there keeps encouraging all patients to get out of bed and walk around as soon as they become able. This is because moving around will help boost blood flow, thus reducing the likelihood of developing a blood clot.(6)

  2. Being an Athlete

    Most people do not consider blood clots as something that would affect athletes. What’s more, blood clots are uncommon in young and healthy people, and well, most athletes are healthy and young. It is due to this that blood clots are not usually associated with athletes.

    However, it is a problem that affects athletes. Being healthy, young, and an athlete does not prevent you from developing sudden blood clots. There are several circumstances that put an athlete, and of course, even non-athletes, at a higher risk of developing blood clots. This is why athletes, their trainers, and coaches need to be especially aware of the following risk factors:(7, 8, 9)

    • Dehydration – it can happen during or after a stressful sporting event.
    • Traveling long distances to reach and come back from a competition. This can include travel by car, bus, or plane.(10)
    • Significant trauma.
    • Bone fracture or any major surgery.
    • Immobilization means staying in a cast or brace following an injury.
    • Birth control pills or birth control patches, hormone replacement therapy, or pregnancy.
    • Having a family history of blood clots or DVT.
    • Having a congenital abnormality in the anatomy of the veins.
    • Having an inherited or acquired clotting disorder such as antiphospholipid antibodies, prothrombin 20210 mutation, Factor V Leiden, and others.(11)
    • May-Thurner Syndrome, which causes narrowing of the major left pelvic vein.(12)
    • Cervical rib causing a thoracic outlet obstruction.
    • Absence of or narrowing of the inferior vena cava, which is the main vein located in the abdomen.

    If you are an athlete, regardless of whether a blood clot is there in your arm or your leg (more likely), here are some of the common symptoms to watch out for:

    • Swelling
    • Pain or tenderness
    • The area where it is hurting will feel warm to the touch.
    • The skin has a red or blue color.
  3. Being Overweight Or Obese

    People who are overweight or obese are twice as likely to develop a blood clot in their leg as compared to those who have a normal weight. This is because obesity is known to cause chronic inflammation throughout the body along with reduced fibrinolysis, which is the ability of the body to break down blood clots.

    A study published in the Journal of Internal Medicine in May 2015 found that there is a direct relationship between obesity and the risk of developing blood clots or DVT. While the reasons behind why being overweight increases the risk of having a DVT are not exactly clear, but the evidence is clear that as a person’s weight increases, so does the risk of DVT.(13)

    It is known that chronic inflammation happens as a result of being deficient in nitric oxide in the body. Nitric oxide is an essential molecule that helps protect the specialized endothelium, which is the lining of blood vessels in the body, and it prevents cells from sticking to the surface of the endothelium. In fact, even at an early age, people who are overweight or obese are known to have dramatically lower levels of nitric oxide in the body. It is believed that it is due to this reduced level of nitric oxide in obese or overweight people that increases the damage to the lining of the blood vessels, which in turn increases the risk of having blood clots.(14, 15)

  4. Smoking

    Smoking is known to increase the risk of developing blood clots nearly three times.(16) Similar to what happens in people who are obese or overweight, smoking also reduces the levels of nitric oxide in the body while also encouraging the blood to stick together and form clots.(17, 18)

    This process is further driven by the dramatically high levels of fibrinogen, which is an essential component in the process of blood clotting in the blood of smokers. Chemicals present in cigarettes are also known to cause the platelets in the blood to clump together. When you combine all these factors, smokers end up having thicker blood, which makes it much more difficult for their hearts to pump blood around the body. This, in turn, causes damage to the inner lining of the blood vessels.

  5. Birth Control Pills

    Now, this is definitely one surprising cause of blood clots that most women would not think about! Women who are taking a combined oral contraceptive pill that contains artificial progesterone and estrogen have been found to slightly increase the risk of having blood clots.(19)

    In fact, that’s not all since other oral contraceptives also show a similar level of increase in the risk of blood clots. It is estimated that nearly 6 to 17 different events per 10,000 women are treated depending on the drug they use, as compared to those women who do not take any oral contraceptive. The ingredients present in contraceptives are known to increase the level of numerous clotting factors present in the blood, thus increasing the chances of blood-forming clots in the veins.(20, 21)


Blood clotting is a very important process in the human body. Clotting prevents excessive loss of blood, both outside and inside the body, when we get hurt. There can be many surprising causes of blood clots, and in recent years, there has been a revolution of new drugs that have made it easier to treat blood clots. This class of drugs is known as direct oral anticoagulants, and they are effective and less cumbersome to use as compared to the old methods of treating blood clots. If you think you are at a high risk of developing blood clots, you should talk to your doctor about what steps you can take to lower your risk.


  1. Olaf, M. and Cooney, R., 2017. Deep venous thrombosis. Emergency Medicine Clinics, 35(4), pp.743-770.
  2. Useche, J.N., de Castro, A.M.F., Galvis, G.E., Mantilla, R.A. and Ariza, A., 2008. Use of US in the evaluation of patients with symptoms of deep venous thrombosis of the lower extremities. Radiographics, 28(6), pp.1785-1797.
  3. Anon, NHS choices. Available at: https://www.uhs.nhs.uk/for-patients/your-stay-in-hospital/making-your-stay-with-us-safe/reducing-the-risk-of-blood-clots [Accessed September 3, 2022].
  4. Anon, 2022. Blood clot info: Risks, symptoms, and prevention. Blood Clots. Available at: https://www.stoptheclot.org/about-clots/blood-clot-info/ [Accessed September 3, 2022].
  5. Anon, 2022. Know the risks, signs & symptoms of blood clots. Centers for Disease Control and Prevention. Available at: https://www.cdc.gov/ncbddd/dvt/infographic-risk.html [Accessed September 3, 2022].
  6. Huber, O., Bounameaux, H., Borst, F. and Rohner, A., 1992. Postoperative pulmonary embolism after hospital discharge: an underestimated risk. Archives of Surgery, 127(3), pp.310-313.
  7. Berkowitz, J.N. and Moll, S., 2017. Athletes and blood clots: individualized, intermittent anticoagulation management. Journal of Thrombosis and Haemostasis, 15(6), pp.1051-1054.
  8. Eichner, E.R., 2014. Clots and consequences in athletes. Current Sports Medicine Reports, 13(5), pp.287-288.
  9. Morrison, G.C., 2007. Blood Clots and the athlete: a review of deep vein thrombosis in sports. International Journal of Athletic Therapy and Training, 12(4), pp.2-4.
  10. Eichner, E.R., 2009. Blood clots and plane flights. Current Sports Medicine Reports, 8(3), pp.106-107.
  11. Erickson, K. and Powers, M.E., 2013. Factor V leiden thrombophilia in a female collegiate soccer athlete: a case report. Journal of Athletic Training, 48(3), pp.431-435.
  12. Raffini, L., Raybagkar, D., Cahill, A.M., Kaye, R., Blumenstein, M. and Manno, C., 2006. May–Thurner syndrome (iliac vein compression) and thrombosis in adolescents. Pediatric blood & cancer, 47(6), pp.834-838.
  13. Klovaite, J., Benn, M. and Nordestgaard, B.G., 2015. Obesity as a causal risk factor for deep venous thrombosis: a M endelian randomization study. Journal of internal medicine, 277(5), pp.573-584.
  14. Zang, Y., Popat, K.C. and Reynolds, M.M., 2018. Nitric oxide-mediated fibrinogen deposition prevents platelet adhesion and activation. Biointerphases, 13(6), p.06E403.
  15. Butler, A.R. and Williams, D.L.H., 1993. The physiological role of nitric oxide. Chemical Society Reviews, 22(4), pp.233-241.
  16. Severinsen, M.T., Kristensen, S.R., Johnsen, S.P., Dethlefsen, C., Tjønneland, A. and Overvad, K., 2009. Smoking and venous thromboembolism: a Danish follow‐up study. Journal of thrombosis and haemostasis, 7(8), pp.1297-1303.
  17. Nielsen, V.G., Hafner, D.T. and Steinbrenner, E.B., 2013. Tobacco smoke-induced hypercoagulation in human plasma: role of carbon monoxide. Blood Coagulation & Fibrinolysis, 24(4), pp.405-410.
  18. Messner, B. and Bernhard, D., 2014. Smoking and cardiovascular disease: mechanisms of endothelial dysfunction and early atherogenesis. Arteriosclerosis, thrombosis, and vascular biology, 34(3), pp.509-515.
  19. Anon, NHS choices. Available at: https://www.nhs.uk/conditions/contraception/combined-contraceptive-pill/ [Accessed September 3, 2022].
  20. Vinogradova, Y., Coupland, C. and Hippisley-Cox, J., 2015. Use of combined oral contraceptives and risk of venous thromboembolism: nested case-control studies using the QResearch and CPRD databases. bmj, 350, p.h2135.
  21. Previtali, E., Bucciarelli, P., Passamonti, S.M. and Martinelli, I., 2011. Risk factors for venous and arterial thrombosis. Blood Transfusion, 9(2), p.120.
Team PainAssist
Team PainAssist
Written, Edited or Reviewed By: Team PainAssist, Pain Assist Inc. This article does not provide medical advice. See disclaimer
Last Modified On:September 15, 2022

Recent Posts

Related Posts