High Homocysteine: What It Means for Your Heart

Homocysteine is an amino acid your body clears with the help of folate, vitamin B12 and vitamin B6. A high level tells you something about those vitamins and your kidneys. What it tells you about your heart is less than it first appears.

Medically reviewed · Guideline-anchored · Updated Oct 7, 2026

Reviewed by Dr. Prahlad Rai Gupta, MBBS, MD · Thresholds anchored to Cochrane 2017, VISP, HOPE-2, NORVIT & CSPPT trial evidence · Evidence & Methodology

Based on JAMA, NEJM & Cochrane trial evidence 234 markers analysed Free, no account needed

Elevated homocysteine, above 15 µmol/L, is linked with more heart disease and stroke, but it is a marker of risk, not a proven cause. Trials that lowered homocysteine with folic acid, B6 and B12 (VISP, HOPE-2 and NORVIT) did not cut their main cardiovascular outcomes. A 2017 Cochrane review found no effect on heart attacks and a small drop in strokes. A high result is a reason to check B12, folate and kidney function, and to look hard at LDL, blood pressure and smoking. FixFirst flags homocysteine above 10 µmol/L as borderline and above 15 as elevated, and reads it next to your B12, folate, eGFR and LDL.

Homocysteine levels: what counts as high

These are the tiers FixFirst applies to a homocysteine result. Your lab prints its own range too, so read the number against both.

Homocysteine (µmol/L)	How FixFirst reads it	What it means
10 or below	Not flagged	Within the range FixFirst treats as normal.
Above 10 to 15	Borderline	Check B12, folate and kidney function before reading anything into it.
Above 15	Elevated	Hyperhomocysteinaemia. Linked with more heart disease and stroke in observational studies.

Some labs report mg/L. FixFirst converts it (1 mg/L ≈ 7.4 µmol/L).

How homocysteine relates to heart disease and stroke

The Homocysteine Studies Collaboration pooled 30 studies in a 2002 JAMA meta-analysis. In the prospective studies, after adjusting for known risk factors, a 25% lower usual homocysteine level (about 3 µmol/L) went with an 11% lower risk of ischaemic heart disease and a 19% lower risk of stroke. That is a modest association, not a large one.

Association is not cause. People with high homocysteine also tend to have lower B-vitamin intake and poorer kidney function, so the test of cause is to lower it and watch what happens. The trials below did that.

Homocysteine is not part of standard heart-risk scoring. The 2018 AHA/ACC cholesterol guideline lists risk-enhancing factors such as raised hs-CRP, Lp(a) and ApoB; homocysteine is not among them. LDL carries far more weight in that framework.

What happened when trials lowered homocysteine

Four large randomised trials and one Cochrane review. None showed that lowering homocysteine prevents heart attacks.

Trial	Who took part	What they took	Cardiovascular result
VISP (Toole, JAMA 2004)	3,680 adults after a non-disabling stroke	High-dose vs low-dose folic acid, B6 and B12	No difference in recurrent stroke, heart events or death
HOPE-2 (Lonn, NEJM 2006)	5,522 adults aged 55 or older with vascular disease or diabetes	Folic acid 2.5 mg, B6 50 mg and B12 1 mg vs placebo	No reduction in the combined rate of cardiovascular death, heart attack and stroke. Fewer strokes (relative risk 0.75) as a secondary result
NORVIT (Bønaa, NEJM 2006)	3,749 people after a heart attack	Folic acid and B12, with or without B6, vs B6 alone or placebo	No benefit. A trend toward harm with the full three-vitamin combination (relative risk 1.22, 95% CI 1.00 to 1.50)
CSPPT (Huo, JAMA 2015)	20,702 adults with high blood pressure in China, no prior stroke or heart attack	Enalapril plus folic acid 0.8 mg vs enalapril alone	21% fewer first strokes (hazard ratio 0.79). No difference in heart attack
Cochrane review (Martí-Carvajal, 2017)	15 trials, 71,422 people	B-vitamin homocysteine lowering vs placebo or low dose	No effect on heart attack or death from any cause. Stroke risk ratio 0.90 (95% CI 0.82 to 0.99)

Only the stroke signal repeats (CSPPT, a HOPE-2 secondary result, Cochrane). It has not translated into any heart-attack benefit. The US has fortified grain with folic acid since 1998, so results from one population may not carry over to another.

What raises homocysteine

A high result usually has a correctable driver. These are the ones worth ruling out first.

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Low vitamin B12

B12 is one of three vitamins that clear homocysteine. Plant-based diets and metformin both lower B12. See low vitamin B12.

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Low folate

Serum folate sits on the same report as B12 in many panels. When folate runs low, homocysteine rises because it cannot be converted back to methionine (NIH Office of Dietary Supplements).

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Low vitamin B6

B6 is the third vitamin in the pathway.

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Reduced kidney function

The kidneys clear homocysteine, so a lower eGFR goes with a higher level. Check eGFR on the same report with the eGFR calculator.

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Underactive thyroid

A meta-analysis found raised homocysteine in overt hypothyroidism but not in subclinical hypothyroidism, and levels fell with levothyroxine (Zhou 2014). Check TSH: see the TSH blood test guide.

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Two copies of the MTHFR 677C>T variant

This common gene variant reduces how well the body converts folate to its active form, which can raise homocysteine (NIH Office of Dietary Supplements). About 10% of people of European or Asian ancestry carry two copies.

What to do with a high homocysteine

Fix the drivers you can measure, then put heart-risk effort where trials show a payoff.

Check B12, folate, eGFR and TSH

These four cover the correctable causes in the list above.

Correct a deficiency you actually have

Check B12 before taking folic acid alone. Large amounts of folate can correct the anaemia of B12 deficiency without correcting the nerve damage (NIH Office of Dietary Supplements). Take B vitamins to fix a shortfall, not to protect your heart.

Put heart-risk effort where trials show benefit

LDL or ApoB (see the lipid panel guide), blood pressure, smoking and glucose all have trial evidence behind them. The B-vitamin trials above do not.

Retest 8 to 12 weeks after correcting B12 or folate

B-vitamin supplementation lowers homocysteine measurably within 4 to 8 weeks. A retest at 8 to 12 weeks shows whether the driver was the one you fixed.

Frequently asked questions

What is a normal homocysteine level?

FixFirst does not flag a homocysteine of 10 µmol/L or below, treats above 10 to 15 as borderline, and flags above 15 as elevated. Your lab prints its own reference range, and it may differ, so read your number against both. Some labs report mg/L; 1 mg/L is about 7.4 µmol/L.

Does lowering homocysteine prevent heart attacks?

In trials, no. VISP, HOPE-2 and NORVIT lowered homocysteine with folic acid, B6 and B12 and did not reduce their main cardiovascular outcomes. A 2017 Cochrane review of 15 trials and 71,422 people found no effect on heart attack or death from any cause, and a small reduction in stroke (risk ratio 0.90). The stroke signal also appeared in CSPPT, a trial of adults with high blood pressure in China.

What causes high homocysteine?

Low B12, low folate and low B6 are the common drivers, along with reduced kidney function, an underactive thyroid and two copies of the MTHFR 677C>T variant. Plant-based diets and metformin can lower B12, which indirectly raises homocysteine.

Should I take B vitamins if my homocysteine is high?

Take them to correct a deficiency you have, not to protect your heart. The trials above show that lowering homocysteine with B vitamins did not prevent heart attacks. Check your B12 first: large amounts of folate can correct the anaemia of B12 deficiency without correcting the nerve damage, so folic acid alone can hide a B12 problem.

Is homocysteine used to calculate heart disease risk?

No. The 2018 AHA/ACC cholesterol guideline lists risk-enhancing factors such as raised hs-CRP, Lp(a) and ApoB. Homocysteine is not on that list. Cholesterol, blood pressure, diabetes and smoking drive the standard risk estimate. High LDL cholesterol covers how LDL fits into it.

How long does homocysteine take to come down?

B-vitamin supplementation lowers homocysteine measurably within 4 to 8 weeks. Retest at 8 to 12 weeks after correcting a B12 or folate shortfall, using the same lab, to see whether the driver was the one you fixed.

References & Guidelines

Medical disclaimer: FixFirst is an educational tool, not a medical device. A high homocysteine result needs a doctor to look at the cause, particularly when it is above 15 µmol/L or comes with a history of stroke or heart disease. Always consult a licensed healthcare provider before starting supplements or acting on a homocysteine result.

Keep reading: High LDL Cholesterol · Low Vitamin B12 · Borderline Blood Test Results

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