What the value means
Homocysteine is an amino acid formed during the breakdown of methionine, and its further processing requires vitamin B12, folate and B6. The upper limit of the reference range is usually between 12 and 15 µmol/L depending on the laboratory and rises with age, so 14 µmol/L may still be “normal” on your report. In large population studies, however, higher values are linked to a greater risk of cardiovascular disease, stroke and cognitive decline. An important nuance: trials that lowered homocysteine with B vitamins did not clearly reduce heart attacks; benefits for stroke and the brain were seen only in certain groups. Homocysteine is therefore mainly a useful marker that leads to the underlying cause.
Possible causes
- Vitamin B12 deficiency – common with plant-based diets, in older age and with long-term use of some medicines.
- Low folate and B6 – little vegetables, legumes and whole grains.
- Kidney function – homocysteine rises when it is reduced.
- Genetics – some MTHFR gene variants raise homocysteine, mainly when folate intake is low.
- Lifestyle – smoking, higher alcohol intake, lack of exercise.
- Underactive thyroid – can raise homocysteine slightly.
What you can do
- Further tests – B12 (ideally also active B12 or methylmalonic acid), folate, creatinine and TSH.
- Diet – leafy greens, legumes, whole grains; sources of B12 are meat, fish, eggs and dairy.
- Plant-based diet – on a vegan diet, B12 supplementation is a necessity, not an option.
- Supplements – a B-vitamin complex makes sense mainly for a confirmed deficiency; discuss the choice with your doctor or pharmacist.
- Follow-up – recheck homocysteine after 2–3 months, fasting.
When to see a doctor
See a doctor if your B12 or folate is low, or if you have tingling in your hands and feet, memory problems, anaemia, kidney disease, a family history of cardiovascular disease, or a markedly raised homocysteine (above 20 µmol/L). Also tell your doctor which medicines you take.