The homocysteine bands
| Homocysteine, µmol/L | Band | What this line is |
|---|---|---|
| Under 8 | Optimal | Phoenix choice. It sits inside the normal lab range, with a margin below the consensus line. |
| 8 to 11 | Monitor | Phoenix band. "Monitor" means worth working on. |
| Above 11 | Talk to your doctor | Consensus line (Smith, 2018). Bring it to your next appointment. It is not an emergency. |
"Under 8" excludes 8, so a result of 8.0 is Monitor. The Monitor band includes both ends, so 11.0 is still Monitor and 11.1 is Talk to your doctor.
Confidence: the 11 line is moderate, because it comes from an expert consensus built on trials and cohorts. The under-8 line is low to moderate: it is a Phoenix choice, and no trial has compared under 8 with 8 to 11.
Why does homocysteine matter for your brain?
Raised homocysteine is one of the few dementia risk factors that is cheap and safe to lower, and lowering it slowed brain shrinkage in a randomized trial.
- The consensus. Experts reviewing 20 years of evidence concluded that raised homocysteine is a modifiable risk factor for cognitive decline, dementia and Alzheimer's in older people. For moderately raised levels, still inside the normal range, the relative risk of dementia ran from 1.15 to 2.5 across studies. They named a level above 11 µmol/L as one of the causes of age-related cognitive decline and dementia (Smith, 2018).
- Framingham. In 1,092 older adults followed for 8 years, a homocysteine above 14 µmol/L went with nearly double the rate of Alzheimer's (Seshadri, 2002).
- The VITACOG trial. 271 people over 70 with mild memory problems took folic acid (0.8 mg), vitamin B12 (0.5 mg) and vitamin B6 (20 mg) a day, or a placebo, for two years. On MRI, brains shrank 0.76% a year with the vitamins against 1.08% with placebo, about 30% slower. In people who started above 13 µmol/L, shrinkage was 53% slower (Smith, 2010).
- Omega-3 decides who benefits. In the same trial, B vitamins slowed brain shrinkage by 40% in people with high blood omega-3 levels, and did nothing in people with low levels (Jernerén, 2015). With good omega-3 status, 33% of the vitamin group ended the trial with measurable clinical impairment, against 59% on placebo (Oulhaj, 2016). That is why Phoenix reads homocysteine next to your omega-3 index.
What does APOE4 change?
APOE4 does not come with its own homocysteine number, and the carrier data point in two directions.
- In 4,553 older adults in the TUDA study, 1,205 of them carriers, APOE4 interacted badly with high homocysteine and with low vitamin B12: carriers with either did worse on cognitive tests (Gordon, 2025).
- In people already diagnosed with Alzheimer's and other brain diseases, the links between homocysteine and brain damage markers showed up mainly in non-carriers (Lin, 2025).
Read together: a high homocysteine is worth fixing whatever your genotype, and nothing supports a stricter line for 4/4 than for 3/4. Phoenix uses one line for every carrier.
What did Phoenix choose, and why?
I chose under 8 µmol/L as Phoenix's optimal line for three reasons.
- The consensus line is 11, and dementia risk climbs across the normal range, not only above it (Smith, 2018). Under 8 keeps a clear margin below 11.
- It is reachable. Folic acid plus vitamin B12 typically takes a homocysteine of 12 down to 8 or 9 (Homocysteine Lowering Trialists' Collaboration, 1998). A target nobody can hit helps nobody.
- In VITACOG, the biggest brain benefit was in people who started above 13 (Smith, 2010). Under 8 sits well clear of that zone.
Some clinicians aim for 6 to 7 µmol/L. No study shows that 6 beats 7.9, so Phoenix does not push lower than 8.
What moves homocysteine?
Here are the levers, ranked by how much they lower homocysteine in trials. These are facts about what each one does, not a prescription: the right choice depends on your B12, folate and kidney results, which your doctor can read.
- Folic acid: about 23 to 25% lower. In 25 trials with 2,596 people, daily folic acid lowered homocysteine by 13% at 0.2 mg, 20% at 0.4 mg, 23% at 0.8 mg and 25% at 5 mg, measured from a typical starting level of 12 µmol/L. Doses of 0.8 mg or more gave the full effect; 0.4 mg gave 90% of it. The drop is bigger when homocysteine starts higher and folate starts lower (Homocysteine Lowering Trialists' Collaboration, 2005).
- Vitamin B12: about 7% more on top. Adding about 0.4 to 0.5 mg of B12 a day lowered homocysteine a further 7% (Homocysteine Lowering Trialists' Collaboration, 1998 and 2005). Together, folic acid and B12 typically lower it by a quarter to a third. Across 11 large trials with 22,000 people, B-vitamin treatment lowered homocysteine by 26 to 28% (Clarke, 2014).
- Methylfolate works at least as well as folic acid. In a 24-week trial, a low dose of L-methylfolate (113 µg) lowered homocysteine by 14.6% against placebo, and an equal amount of folic acid (100 µg) by 9.3% (Venn, 2003).
- Betaine (TMG): about 1.2 to 1.3 µmol/L lower, with a cholesterol cost at high doses. Betaine at 4 g a day or more lowered homocysteine by 1.23 µmol/L (McRae, 2013). A larger meta-analysis found a 1.30 µmol/L drop, but also total cholesterol up by about 14 mg/dL and LDL up by about 10 mg/dL. Doses under 4 g a day lowered homocysteine without the lipid rise (Ashtary-Larky, 2022). For a carrier also working on ApoB, that trade matters.
- Vitamin B6: no extra effect. B6 did not lower fasting homocysteine further once folic acid was in place (Homocysteine Lowering Trialists' Collaboration, 2005).
What Phoenix members use: among Phoenix members who log their supplements, 142 have logged a B vitamin (a B-complex, folate, B12, B6 or TMG), and 137 log one as taking now (2 October 2026).
How often should you retest?
No guideline sets a retest interval for homocysteine. The trials above measured their effects after weeks to months of daily supplements; the methylfolate trial checked at 8, 16 and 24 weeks (Venn, 2003).
Phoenix practice: retest about three months after you start or change a B vitamin, so the change has had time to show. Once you are under 8, keep homocysteine in your regular panel.
In practice, the 59 Phoenix members who uploaded two or more homocysteine results waited a median of 235 days between their first and latest test.
What Phoenix members' results show
Start with the whole group. 151 Phoenix members who uploaded their results have a homocysteine test on file (2 October 2026; 84 carry 4/4 and 50 carry 3/4). Their median latest result is 8.2 µmol/L, just over the Phoenix line.
| Latest result | Members | Share |
|---|---|---|
| Under 8 (optimal) | 66 | 44% |
| 8 to 11 (monitor) | 62 | 41% |
| Above 11 (talk to your doctor) | 23 | 15% |
Among the 84 members with 4/4, 45% are under 8, 38% are at 8 to 11 and 17% are above 11.
59 members have tested twice or more, a median of 235 days apart. Their median fell from 8.3 to 7.8 µmol/L, and 11 of the 32 who started at 8 or above finished under 8. The 33 members with 4/4 who retested brought their median from 9.1 to 7.8 µmol/L: from Monitor to under the Phoenix line.
In Phoenix's first research release (476 paying members), 22 of 49 repeat testers improved their homocysteine, 14 held steady and 13 got worse.
One case: vitamin B12 took an APOE4/4 man in his 50s from 10.5 to 7.5 µmol/L (-28.6%) in 139 days, from Monitor to under the Phoenix line. His stack also included magnesium threonate, folate and a B-complex.
Members chose their own supplements, and many changed more than one thing at a time. Every figure here is an anonymous aggregate or a de-identified case.
When should you talk to your doctor?
Talk to your doctor if your homocysteine is above 11 µmol/L. That is the consensus line (Smith, 2018). Bring it to your next appointment; it is not an emergency.
Also bring it up if your result stays above 8 after three months of B vitamins. A doctor can check your vitamin B12 status (methylmalonic acid is the usual follow-up test), your folate and your kidney function, and review what you already take. Higher supplement doses are not automatically better.
If you take a prescribed medicine or vitamin, do not change it because of this page.