# Homocysteine

Source: https://synapse-lifestyle.com/en/reference-guide/biomarkers/homocysteine

Unit: μmol/L

## What is Homocysteine?

Homocysteine is an amino acid that your body normally breaks down again with the help of B vitamins. A raised value often points to a shortage of those vitamins. Staying neatly within range supports your blood vessels and your nervous system. It's a marker you can often adjust well with diet.

## Clinical frame

Homocysteine is a sulphur-containing amino acid from methionine metabolism. Its breakdown requires **folate, vitamin B12 and B6**, so deficiencies, MTHFR variants and renal insufficiency raise the level. Observationally, an elevated value is associated with mortality, atherosclerosis, peripheral arterial disease, venous thrombosis and stroke, with a continuous, dose-dependent relationship [1].

The causal role is **vascular-bed specific**: genetic studies support an effect on stroke, especially ischaemic and small-vessel stroke, but not on coronary disease, heart failure or atrial fibrillation. Large trials with B vitamins lowered homocysteine by a quarter without fewer infarctions or deaths, with at most a small reduction in strokes [2] [3].

A moderate elevation is therefore above all a **weak risk marker**, not a treatment target in itself. Above about 30 μmol/L the meaning changes: the value then usually points to a B12 or folate deficiency, a hereditary enzyme defect or kidney failure and warrants targeted diagnostics and correction [1] [3].

## What moves this value?

Too little folate, vitamin B12 or B6 is the most common cause. Heredity and your kidney function also play a part.

Green vegetables (folate), wholegrain products and enough B12 support this. Easy to retest after a few months. Discuss a persistently high value with your doctor.

## What this connects

- [hsCRP](https://synapse-lifestyle.com/en/reference-guide/biomarkers/hs-crp)
- [Vitamin B12](https://synapse-lifestyle.com/en/reference-guide/biomarkers/vitamin-b12)

Developed and reviewed with the Synapse [medical advisory board](https://synapse-lifestyle.com/en/advisory-board).

## References

1. Smith, A. D. & Refsum, H. Homocysteine - from disease biomarker to disease prevention. J Intern Med 290, 826–854 (2021). https://doi.org/10.1111/joim.13279
2. Yuan, S., Mason, A. M., Carter, P., Burgess, S. & Larsson, S. C. Homocysteine, B vitamins, and cardiovascular disease: a Mendelian randomization study. BMC Med 19, 97 (2021). https://doi.org/10.1186/s12916-021-01977-8
3. Martí-Carvajal, A. J., Solà, I., Lathyris, D. & Dayer, M. Homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database Syst Rev 8, CD006612 (2017). https://doi.org/10.1002/14651858.CD006612.pub5

- [Read more in the reference guide](https://synapse-lifestyle.com/en/reference-guide/heart#Consequence-CSCardiacHealth-FHomocysteine)
- [All biomarkers in the guide](https://synapse-lifestyle.com/en/reference-guide#biomarkers)

The colour zones are personal: they depend on age, sex, risk and history, and appear in the patient's own report.

Insights to discuss with the patient, not a diagnostic instrument.