Vitamin B12

Vitamin B12, cobalamin, does two things you cannot do without. It is needed to make DNA, and so for every cell that divides, with the making of red blood cells as the place where that shows first. And it is needed for the insulating layer around your nerves, which is why a deficiency starts with tingling and numbness in feet and hands. B12 works together with folate in this, and the two clear homocysteine together. B12 comes almost only from animal food: meat, fish, eggs and dairy. Plants do not make it. Its uptake is a relay, too. Stomach acid frees B12 from food, the stomach lining makes a protein, intrinsic factor, that binds to B12, and that package is only absorbed in the last stretch of the small intestine. If one of those steps falters, uptake drops, even with a plate full of meat. What you do absorb, your liver keeps for years, and that is why a deficiency develops slowly and stays unnoticed for a long time. Your report shows vitamin B12 in pmol/L. Normal is about 175 to 569 pmol/L where the labs overlap, with a lower limit that differs per lab. The number measures the total B12 in your blood, and that does not always say whether your cells have enough; methylmalonic acid and homocysteine fill that gap.

A B12 deficiency is one of the most missed deficiencies, because it comes so slowly. Your liver holds a store of years, so anyone who switches to plant-based eating or starts antacids notices nothing for a long time. Then the symptoms come: tiredness that does not pass, tingling and numbness in feet and hands, an unsteady feeling when walking, forgetfulness, low mood, a sore tongue. The anaemia in the textbooks often comes only later, or not at all. And the part you least want to miss, the nerve damage, can become permanent if the deficiency lasts long enough. That is the reason to know your B12 before there are symptoms, if you belong to one of the groups in which uptake falters. Those groups are clear. Anyone who eats vegetarian or vegan takes in too little and needs a supplement, full stop. Anyone on antacids no longer frees B12 from food. Anyone on metformin absorbs less in the gut. Anyone getting older makes less stomach acid and less intrinsic factor. Anyone using nitrous oxide puts the B12 that is there out of action, and with regular use that gives nerve damage within months at a normal store. And in pernicious anaemia the production of intrinsic factor is lost to an autoimmune reaction; no food helps then. The good part is that a deficiency is very reversible, and cheap. A high-dose tablet works in almost everyone, even with poor uptake, because a small share always gets in without intrinsic factor; injections exist for anyone in whom that fails. The earlier you start, the more of the nerve symptoms reverse.

A low B12 means the supply falls short or the uptake falters. In order of how often it occurs: plant-based eating, antacids, getting older, metformin, and then heavy drinking, stomach surgery or gut disease, pernicious anaemia and nitrous oxide. A value below the lower limit with symptoms is a reason to top up; a value below the lower limit without symptoms is a reason to look at where it comes from and to adjust your diet or add a supplement. In between lies the grey zone, roughly between the lower limit and 250 pmol/L. The total B12 in your blood says little there, because part of that B12 is bound to a protein that does not hand it over to your cells. Methylmalonic acid and homocysteine show whether your cells are running short: methylmalonic acid rises only with a B12 deficiency, homocysteine also with a folate or B6 deficiency. A normal B12 with symptoms and a high methylmalonic acid is a deficiency; a low B12 with a normal methylmalonic acid and no symptoms usually is not. A high B12 is almost always a supplement or an injection and no cause for concern; what you have too much of, you pass in the urine. Without a supplement a high B12 is rare and a look at the liver belongs with it. Take note: once you have started topping up, the total B12 shoots up while the cells are not yet refilled. The number then says nothing more about the deficiency; methylmalonic acid and the symptoms do.