High blood pressure, elevated LDL cholesterol, low HDL, type-II diabetes, metabolic syndrome, obesity, smoking, age, and male gender; What comes to mind when these risk factors for health are mentioned? Cardiovascular diseases (CVD), such as Heart diseases and stroke, of course! However, there is one major CVD risk factor is linked to all the other risk factors but is less well known. Blood viscosity, i.e. the thickness or stickiness of your blood, can influence your chances of having a heart attack or suffering a stroke. In fact, the thicker your blood is, the riskier you are [1,2].

Blood viscosity and CVD risk
Viscosity of liquid is a measure of its resistance to flow. The higher the viscosity, the harder for it to flow. Obviously, honey is harder to flow when compared to water, thus honey has a higher viscosity than water.

High blood viscosity negatively impacts the cardiovascular health. It is linked to the formation of plaque build-up in blood vessels (atherosclerosis), hypertension, and the risk of blood clot (thrombus) formation [3]. A major study that examined the occurrence of heart attack and stroke among 1592 men and women aged 55-74 years found that those who experienced heart attack and stroke had significantly higher blood viscosity than those who did not [4]. Hence, increased blood viscosity is clearly linked to the risk of heart attack and stroke.
What determines blood thickness?

The thickness of blood depends on its content. About half of the content of blood consists of a liquid called plasma and the other half consists of blood cells, including red blood cells which carries oxygen, white blood cells which fights infections, and platelets which help blood to clot. Among these contents, here are the main ones that can affect the thickness of the blood [2]:
- Red blood cells – The higher the ratio of the volume of red blood cells to the total volume of blood (haematocrit) is, the higher the blood viscosity.
- Cholesterol content, especially the content of low-density lipoprotein (LDL), in the blood also affects the thickness of the blood.
- Fibrinogen – a protein chain that circulates in blood that can be converted fibrin during injury to form blood clots.
- Platelets – Increases in platelets increases the blood viscosity
Factors that can influence the thickness of blood include inflammation, smoking, diabetes, high homocysteine level, and genetic [2].
How to thin your blood?

Dr Kenneth R. Kensey, a renowned cardiologist who wrote the books “The Blood Thinner Cure” [5] and “The Origin of Atherosclerosis: What Really Initiates the Inflammatory Process” [5] suggested the following approach to reduce blood viscosity:
- Not smoking
- Maintain a healthy diet
- Exercise regularly
- Reduce stress
- Drink plenty of water
- Donate blood
- Take low-dose aspirin every day
The first five points are common advises to stay healthy which should not come as a surprise.
Blood donation is one way to purposely induce loss of blood and thus reduces the iron content and blood cells in the body which might reduce oxidative stress and blood viscosity and therefore decrease cardiovascular risk in the long term [6].

Aspirin is one of the most commonly used blood “thinning” medication. Aspirin is a type of antiplatelet drug that prevent platelets from sticking together as easily, its use has been shown to reduce the risk of blood clots forming. For this reason, aspirin has been widely used in the long term prevention of stroke and heart attack [7]. However, regular use of aspirin is associated with the significant risk of gastrointestinal bleeding, an unwelcome side-effect [8].
A natural blood thinning food

Nattokinase, an enzyme produced by the Bacillus subtilis Natto during the fermentation of soybeans, has been shown to posses similar antiplatelet effect as aspirin [9]. Research in nattokinase has shown promising effects that it can be a safer, powerful, and low-cost alternative to many blood thinning drugs. A clinical trial study (Phase II) is currently undergoing in the USA for the use of nattokinase in prevention of blood clotting [10]. As such, regular consumption of natto, the Japanese fermented soy beans as well as its derivative food supplement, can be a good way to keep the blood thin.
Check out the following articles to learn more about natto:

Maintaining a healthy circulatory system

Natto – a powerful super food
References
[1] R. Holsworth, J. Wright, Blood viscosity : The unifying parameter in cardiovascular disease risk, Holist. Prim. Care. 13 (2012). https://www.holisticprimarycare.net/topics/topics-a-g/functional-medicine/1297-blood-viscosity-the-unifying-parameter-in-cardiovascular-disease-ri….
[2] Is blood like your waistline – the thinner, the better?, Harvard Heal. Lett. (2014). https://www.health.harvard.edu/newsletter_article/is-blood-like-your-waistline-the-thinner-the-better.
[3] G.A.M. Pop, D.J. Duncker, M. Gardien, P. Vranckx, S. Versluis, D. Hasan, C.J. Slager, The clinical significance of whole blood viscosity in (cardio)vascular medicine., Neth. Heart J. 10 (2002) 512–516. http://www.ncbi.nlm.nih.gov/pubmed/25696056 (accessed February 6, 2018).
[4] G.D. Lowe, A.J. Lee, A. Rumley, J.F. Price, F.G. Fowkes, Blood viscosity and risk of cardiovascular events: the Edinburgh Artery Study., Br. J. Haematol. 96 (1997) 168–73. http://www.ncbi.nlm.nih.gov/pubmed/9012704 (accessed February 6, 2018).
[5] K.R. Kensey, C.A. Turkington, The Blood Thinner Cure, Contemporary Books, Chicago, IL, 2001.
[6] K. Van Den Hurk, K. Peffer, K. Habets, F. Atsma, P.C.M. Pasker-de Jong, P.A.H. Van Noord, I.J.T. Veldhuizen, W.L.A.M. De Kort, Blood donors’ physical characteristics are associated with pre- and post-donation symptoms – Donor InSight., Blood Transfus. 15 (2017) 405–412. doi:10.2450/2016.0023-16.
[7] O. Ogbru, D.L. Kulick, Aspirin Therapy for Heart Attack & Stroke Side Effects & Guidelines, (n.d.). https://www.medicinenet.com/aspirin_and_antiplatelet_medications/article.htm#what_is_aspirin? (accessed February 6, 2018).
[8] E.S. Huang, L.L. Strate, W.W. Ho, S.S. Lee, A.T. Chan, Long-term use of aspirin and the risk of gastrointestinal bleeding., Am. J. Med. 124 (2011) 426–33. doi:10.1016/j.amjmed.2010.12.022.
[9] J.-Y. Jang, T.-S. Kim, J. Cai, J. Kim, Y. Kim, K. Shin, K.S. Kim, S.K. Park, S.-P. Lee, E.-K. Choi, M.H. Rhee, Y.-B. Kim, Nattokinase improves blood flow by inhibiting platelet aggregation and thrombus formation., Lab. Anim. Res. 29 (2013) 221–5. doi:10.5625/lar.2013.29.4.221.
[10] Y. Weng, J. Yao, S. Sparks, K.Y. Wang, Nattokinase: An oral antithrombotic agent for the prevention of cardiovascular disease., Int. J. Mol. Sci. 18 (2017). doi:10.3390/ijms18030523.