Homocysteine – The Unknown Killer

Overview – What is homocysteine?

Homocysteine is an amino acid produced during the process of proteolysis (i.e., breakdown of protein).

Disrupted levels of this amino acid in the blood or urine leads to various signs and symptoms that involve most organ systems.

In this article, we will cover the normal levels of homocysteine, as well as the potential side effects of elevated levels of this amino acid.

What is homocysteinemia?

Homocysteinemia refers to the levels of homocysteine in the blood, which does not necessarily translate into homocystinuria when the concentration is normal. (1)

Similar to homocystinuria, high levels of homocysteine in the blood may be due to a genetic predisposition that activates certain metabolic pathways.

Aside from genes, nutritional and environmental factors (e.g., pharmacological drugs) may all play a role in homocysteinemia. (2)

In general, an elevated level of homocysteine in the blood does not cause any symptoms in adults. However, it can precipitate deficiencies of other vitamins, including vitamin B-12 and vitamin B-9 (i.e., folate).

Symptoms of vitamin B-12 deficiency include:

  • Pale skin
  • Weakness
  • Mouth sores
  • Mood changes
  • Fatigue
  • Tingling sensations in the hands, arms, legs, or feet
  • Dizziness

Symptoms of vitamin B-9 deficiency include:

  • Fatigue
  • Growth problems
  • Mouth sores
  • Tongue swelling

The normal levels of homocysteine

An elevated level of homocysteine is generally referred to as hyperhomocysteinemia, which can lead to blood vessel damage and clot formation. (3)

Moreover, hyperhomocysteinemia often reveals a deficiency in vitamin B12 and B9 (i.e., folate). (4)

According to research, the normal levels of homocysteine in the blood should not exceed 15 micromoles per liter. (5)

Based on this information, hyperhomocysteinemia can be classified into three categories:

  • Moderate hyperhomocysteinemia: 15-30 mcmol/L
  • Intermediate hyperhomocysteinemia: 30-100 mcmol/L
  • Severe hyperhomocysteinemia: greater than 100 mcmol/L

Elevated homocysteinemia and cardiovascular disease

Hyperhomocysteinemia by itself is usually not problematic in adults; however, children may experience specific symptoms. (6)

With that said, researchers found a connection between high levels of homocysteine and an increased risk of heart disease. (7) Interestingly, researchers noted that lowering the levels of homocysteine does not translate into a lower risk of heart disease.

The exact mechanisms that explain why hyperhomocysteinemia is a risk factor for cardiovascular disease are not clear yet. However, preliminary research suggests that the damage caused by this amino acid to the endothelial layer of the blood vessels may precipitate atherosclerosis, which is the hallmark of coronary artery disease and myocardial infarction. (8)

If you suspect that you have irregular levels of homocysteine, you should speak with your primary care physician.

Takeaway message

Homocysteine is an amino acid that serves as an important building block to synthesize new peptides and proteins.

The high levels of this amino acid seem to cause vessel tissue damage, which eventually increases the risk of heart disease.

If you have any questions or concerns about homocysteine or homocysteinemia, please don’t hesitate to share your thoughts in the comment section below or contact us by clicking on this link (insert link of contact us page).


1- https://www.medscape.com/answers/1952251-115696/what-is-homocysteinemia

2- Kumar, A., Palfrey, H. A., Pathak, R., Kadowitz, P. J., Gettys, T. W., & Murthy, S. N. (2017). The metabolism and significance of homocysteine in nutrition and health. Nutrition & metabolism, 14(1), 1-12.

3- Ganguly, P., & Alam, S. F. (2015). Role of homocysteine in the development of cardiovascular disease. Nutrition journal, 14(1), 1-10.

4- Son, P., & Lewis, L. (2020). Hyperhomocysteinemia. In StatPearls [Internet]. StatPearls Publishing.

5- Kumar, A., Palfrey, H. A., Pathak, R., Kadowitz, P. J., Gettys, T. W., & Murthy, S. N. (2017). The metabolism and significance of homocysteine in nutrition and health. Nutrition & metabolism, 14(1), 1-12.

6- Yıldırım, A., Keleş, F., Özdemir, G., Koşger, P., Uçar, B., Alataş, Ö., & Kılıç, Z. (2016). Homocysteine levels in normotensive children of hypertensive parents. Anatolian journal of cardiology, 15(12), 1008.

7- Peng, H. Y., Man, C. F., Xu, J., & Fan, Y. (2015). Elevated homocysteine levels and risk of cardiovascular and all-cause mortality: a meta-analysis of prospective studies. Journal of Zhejiang university-science B, 16(1), 78-86.

8- Pushpakumar, S., Kundu, S., & Sen, U. (2014). Endothelial dysfunction: the link between homocysteine and hydrogen sulfide. Current medicinal chemistry, 21(32), 3662-3672.

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