Homocysteine is an amino acid your body makes itself while breaking down methionine, a protein building block from your food. In most people the value sits below 15 micromol per litre. If it sits higher, that relates to a raised risk of cardiovascular disease. It sounds like a simple story, and that is exactly where it goes wrong.
Because the logical next step, lowering that value and thereby lowering your risk, has been tested in large trials. And it disappointed. I think this is the most underexposed point on the entire Dutch homocysteine internet, so I will start there.
What is homocysteine and what does it do?
Homocysteine is a sulphur-containing amino acid that appears as an intermediate when your body breaks down methionine. Normally your body clears it again, and folate, vitamin B12 and vitamin B6 are needed for that. If the clearing works less well, homocysteine builds up in your blood and the value rises.
So those B vitamins are not a side note, they are the engine of the breakdown. This is why a raised value is often a signal about your vitamin B12 and folate rather than about your vessels.
What does a high homocysteine mean?
A high value usually means the breakdown is stalling. The most common reason is a shortage of folate, B12 or B6. Your kidneys, smoking, heavy alcohol use and some medicines can push the value up too. A hereditary variant in the MTHFR gene sometimes plays a part. A high value is therefore a clue, not a diagnosis.
| What you see | What often sits behind it | What you can look at alongside |
|---|---|---|
| Homocysteine high, B12 low | A B12 shortage slowing the breakdown | Vitamin B12 |
| Homocysteine high, folate low | Too little folate from food | Folate |
| Homocysteine high, B vitamins normal | Sometimes kidney function, lifestyle or genetics | Discuss with your GP |
| Homocysteine normal | The breakdown route is doing its job | No further action needed |
Does homocysteine raise your cardiovascular risk?
It relates to it, but it probably does not drive it. A meta-analysis by the Homocysteine Studies Collaboration found a clear association between higher values and more heart disease and stroke (PMID 12387654). Such an association says nothing about cause. And that difference is decisive here.
The evidence came from the trials. The HOPE-2 study gave over 5,000 people folic acid with B6 and B12: the homocysteine value dropped, but the number of heart attacks and deaths did not (PMID 16531613). A meta-analysis across 8 trials with 37,485 participants saw the same (Clarke et al., PMID 20937919). A Cochrane review from 2017 reached the same conclusion (PMID 28816346).
Imagine two people whose value falls from 18 to 9 micromol per litre after three months of B vitamins. On paper that looks fantastic. Based on those trials there is simply no reason to assume your cardiac risk fell along with it. Homocysteine behaves here like a smoke alarm going off at a fire it did not start.
So why is it still on so many test panels?
Because as a signal it remains useful. A high value often points to a shortage of B12 or folate. That shortage is worth knowing about in itself. The value also adds context to a wider risk picture. What it is not: a target you drive down at all costs.
My position will not please everyone. Have this value drawn without your B12 and folate beside it, and the number gives you little. It is a signpost. Then you also want to see where it points.
For the wider context: see our explainer on ApoB, hs-CRP and homocysteine, and on vitamin B12 deficiency. How homocysteine fits the larger vascular story sits in our pillar on narrowed blood vessels.
How do you have homocysteine measured?
With an ordinary blood draw. You are usually fasting, because a protein-rich meal can lift the value for a while. The tube needs processing quickly, because the value rises if blood stands too long. With a high result, checking your B vitamins is the obvious step. See the homocysteine marker page for the details.
Frequently asked questions
Is homocysteine the same as cholesterol?
No. Cholesterol is a fat that builds up in the vessel wall and relates causally to vascular disease. Homocysteine is an amino acid from your protein metabolism and behaves mainly as a signal.
Should I take B vitamins with a high value?
That is a conversation with your GP, not with a blog. B vitamins lower the value reliably, but that did not prevent cardiovascular disease in trials. With a proven shortage the trade-off looks different.
What I would leave you with
Treat this value as a question, not as a score. Do you get a result above 15 micromol per litre back? Then ask your GP about your B12, your folate and your kidneys. Do that before anything gets swallowed. Every blood test result at Vitalcheck includes a professional assessment from a BIG-registered doctor. Always discuss treatment decisions with your GP.
References
- Homocysteine Studies Collaboration. Homocysteine and risk of ischemic heart disease and stroke: a meta-analysis. JAMA. 2002. PMID 12387654
- Lonn E, et al. Homocysteine lowering with folic acid and B vitamins in vascular disease. New England Journal of Medicine. 2006. PMID 16531613
- Clarke R, et al. Effects of lowering homocysteine levels with B vitamins on cardiovascular disease, cancer, and cause-specific mortality. Archives of Internal Medicine. 2010. PMID 20937919
- Marti-Carvajal AJ, et al. Homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database of Systematic Reviews. 2017. PMID 28816346
- RIVM. Cardiovascular disease: figures and context. Volksgezondheid en Zorg. Accessed 2026.
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