Homocysteine

Every time your body breaks down protein, an intermediate is released from the amino acid methionine: homocysteine. It is a substance you do not want to leave lying around, because in high concentrations it damages the inner lining of your blood vessels. So your body clears it straight away, along two routes. The first converts homocysteine back into methionine, and that needs folate and vitamin B12. The second breaks it down into a substance you pass in the urine, and that route runs on vitamin B6. If both routes work, homocysteine stays low. That makes homocysteine a measure of how well those three vitamins do their work in your cells, and not only of how much of them swims around in your blood. So the value often moves before the folate or the B12 itself drops below the limit. Your kidneys belong to it too: they clear part of the homocysteine, and if they work less, the value rises without there being a vitamin deficiency. Your report shows homocysteine in µmol/L. Normal is about 7 to 15 µmol/L for a man from age 18 and 6 to 13 µmol/L for a woman of 19 to 55 years where the labs overlap; above 15 it is called raised, above 20 markedly raised. It is drawn fasting and the tube has to be processed quickly, because the red blood cells keep releasing homocysteine after the draw.

The first reason to know your homocysteine is that it is an early sign of a B vitamin deficiency, often earlier than the vitamin values themselves. That counts for anyone who eats plant-based, is getting older, uses antacids or metformin, drinks a lot or eats little vegetables. A slightly raised homocysteine in such a person is usually a folate or B12 deficiency in the making, and that is reversed within weeks with vegetables, legumes and where needed a supplement. Methylmalonic acid tells you which of the two it is: that rises only with a B12 deficiency. The second reason is lifestyle in the broad sense. Smoking and plenty of coffee raise homocysteine, little vegetables and fruit do too, and exercise lowers it a little. Some people also carry an inherited variant of the enzyme that prepares folate for the first route, and sit somewhat higher because of it, especially with little folate in the diet. That is not a disease; it means vegetables count a bit harder for you. The third reason is what homocysteine is not. For a long time a high value counted as a risk for heart and vessels, and in research a high value does go together with more heart and vascular disease. But when in large studies homocysteine was lowered markedly with folate and B vitamins, people did not get fewer heart attacks or strokes. A high homocysteine is therefore more a sign of what is already wrong, few vegetables, little B12, smoking, poor kidneys, than a lever you have to pull for your heart. So we measure it for what it does say: your B vitamins.

A high homocysteine is, in order of how often it occurs: a folate deficiency, a vitamin B12 deficiency, reduced kidney function, a vitamin B6 deficiency, medicines such as metformin, methotrexate and some drugs against epilepsy, smoking and plenty of coffee, an inherited predisposition, and rarely an underactive thyroid. A few points above the limit is usually a vitamin matter; a value far above 20 µmol/L deserves a more thorough look, at the kidneys and at an inherited cause too. A low homocysteine is favourable. It means both clearance routes work and that you have enough folate, B12 and B6; in anyone taking a supplement or pregnant, the value often sits at the low end. Nothing belongs with it. Set homocysteine beside folate and vitamin B12, with methylmalonic acid to tell the two apart, beside your kidney function, and with a normal folate and B12 beside vitamin B6. Have blood drawn fasting and compare over time at the same lab.