High levels can be a risk factor for cardiovascular disease, stroke, blood clots, Alzheimer’s, dementia, declining memory, poor concentration and judgment and lowered mood, difficulty conceiving, risk from repeated early miscarriage, migraines, and those with conditions such as diabetes and osteoporosis.
The complex metabolism of homocysteine needs certain cofactors, and deficiencies in vitamin B12, folic acid and vitamin B6 are associated with raised homocysteine levels. Other factors thought to raise levels are poor diet, poor lifestyle – especially smoking and high coffee and alcohol intake, some prescription drugs (such as proton pump inhibitors), diabetes, rheumatoid arthritis and poor thyroid function.
Homocysteine has therefore been shown to play a crucial role as a key marker for disease development determining longevity and health throughout a person’s life. Approximately 20% of women who have a child with a neural tube defect have abnormal homocysteine metabolism.
Raised homocysteine is associated a build-up of damaging free radicals. Oxidation can lead to heart disease, strokes, cancers and autoimmune diseases, vascular damage, cognitive impairment, neurological complications, congenital defects and pregnancy complications.
There is no consensus about the upper reference limits for plasma homocysteine concentrations although the ‘normal’ range for healthy individuals is considered to be between 5 and 15 µmol/L. However levels as low as 6.3 µmol/L are thought to confer an increased risk and each 5 µmol/L can increase the risk of coronary heart disease events by approximately 20%.
Over 6.3µmol/L represents an increased risk of coronary artery disease.
It has been recognized that some people have a common genetic variant (called methylenetetrahydrofolate reductase, abbreviated MTHFR) that impairs their ability to process folate. This defective gene leads to elevated levels of homocysteine in some people who inherit MTHFR variants from both parents.