What are the signs of vitamin B6 deficiency?

Vitamin B6 deficiency causes a particular anaemia, cracked lips, a swollen tongue, depression and confusion, and weakens the immune system.

Who is most likely to run low

People with poor kidney function, including those on dialysis, often have low vitamin B6 levels.

What this means for you

Vitamin B6 deficiency on its own is uncommon, and it usually arrives alongside low levels of other B vitamins rather than by itself.

What it looks like is a particular kind of anaemia, cracked lips and corners of the mouth, a swollen tongue, low mood and confusion, and infections that come more often than they should. That list overlaps with several other deficiencies, which is why a blood test rather than a mirror is what settles it.

Why the evidence here is the shape it is

Almost everything below sits low on our certainty scale, and it is worth knowing why before you read it. To show what a shortage of B6 does to a person, you would have to take a group and deliberately keep them short of it until they got ill. Nobody is going to run that study and nobody should. So what exists is case series, hospital records and counts inside groups already at risk. Better searching does not turn any of that into a randomised trial. A low rating here means the question cannot be answered another way, not that someone looked half-heartedly.

Who actually turns up low

People with reduced kidney function, including those on dialysis, are the group most likely to run low. Some antiepileptic drugs also speed up how fast the vitamin is broken down.

Unsettled. Two more groups have been counted since. In Parkinson's disease, where levodopa uses up B6, 60 of 145 patients had an abnormal level and 52 of those were low rather than high. Low B6 showed up in 44.6 per cent of people on the intestinal gel form of levodopa and 30.1 per cent on the oral one, and nearly every oral case came from doses of 1,000 mg a day or more. The reviewers call their own source literature limited and built out of small observational studies.

Unsettled. Combined oral contraceptives lower B6 as well. In eight young women using them, four weeks of B6 cut depression scores by 20 per cent while the same women rose 11 per cent on placebo, and what they ate stayed at 1.2 to 1.4 mg of B6 a day throughout. Eight people in one crossover trial, called preliminary by the researchers who ran it. It is worth mentioning the pill to a doctor who is looking into low mood, and it is not worth more than that.

Low mood is the one sign tested head on

Unsettled. 267 adults took 100 mg of B6 a day, vitamin B12 or a placebo for a month. Among the 58 who already had mild or worse depression symptoms, B6 lowered those scores against both of the other arms. Anxiety and stress did not move at all. The catch is that the group who benefited was picked out after the randomisation, most of the volunteers were women, and 100 mg a day is far above anything a diet delivers. The authors asked for a proper trial in patients, and it has not been run.

Nerves, and what can honestly be said about them

Not for everyone. Do not treat a suspicion of low B6 with a large supplement. Grams a day taken for a year or more cause severe and progressive nerve damage in the arms and legs, and the upper limit is 100 mg. This is the one water-soluble vitamin where the overdose is worse than the deficiency.

B6 also gets named from the other direction, as a cause of nerve damage when it runs low. Here is the whole of what has been counted. Among 83 people admitted to hospital with acute nerve damage caused by malnutrition, B6 was deficient in 16 per cent, second behind thiamine at 54 per cent. Nearly three quarters of them had had weight-loss surgery. Those are published case reports, so they describe who ends up written up rather than who has low B6, and the symptoms recorded in that group belong to nutritional nerve damage in general.

Unsettled. Low B6 also tracks with how bad a neurological disease already is. In 99 people with multiple sclerosis, disability scores correlated with blood B6 at minus 0.32. A correlation found inside a trial built for something else cannot say which way it runs. Worse disease driving B6 down fits those numbers just as well as the reverse.

Unsettled. B6 is widely sold for premenstrual symptoms, morning sickness and carpal tunnel. The evidence for those uses is mixed, and a systematic review of 14 randomised trials found insufficient evidence that B6 affects cognitive function at all.

The line between normal and low may be in the wrong place

Unsettled. A blood test for B6 measures plasma pyridoxal-5'-phosphate, and 30 nmol/L is treated as sufficient. The intake recommendations are built on that number. A more sensitive metabolic marker starts moving when PLP falls below 100 nmol/L, and moves faster below 50. If that marker is picking up something real, a person can be biochemically short of B6 while their test result comes back normal. Nobody has yet shown that this matters to how anyone feels, so it is a reason to watch the field rather than to act. It is also a reason not to read a normal result as the end of a conversation if the symptoms are still there.

Who runs short, counted properly

Beyond the clinical groups above, ordinary intake data show a clear pattern. The share of people below the requirement climbs with age, and climbs much further for women. Among girls aged 4 to 8 it is 5.1 per cent. At 14 to 18 it is 38.1 per cent. At 51 to 70 it is 52.4 per cent, and past 70 it is 52.8 per cent. Men are lower at every age band, from 4.1 per cent in childhood to 36.8 per cent past 70. The requirement itself rises after 50, which accounts for part of the climb.

One thing that pushes people over that line quietly is the kind of food the B6 comes from. Most of the B6 in plants is bound to a sugar, and it is used at roughly 58 per cent of the rate of the free form. Women fed two diets with nearly identical B6 on paper, 1.52 against 1.44 mg a day, came out measurably worse off on the one where more of it was plant-bound. So an older woman eating mostly plants can be short while her food diary says she is fine.

This is the one deficiency page where the treatment can cause the disease. The numbness and tingling that low B6 produces are the same symptoms an excess produces, and a review of that literature concluded that more than 50 mg a day for an extended stretch may be harmful and should be discouraged. So if your hands tingle, the answer is a test and a clinician rather than a 100 mg tablet taken indefinitely. The one B6 use with real trial support is nausea in early pregnancy, where a pooled analysis of 18 studies found a real improvement at doses a doctor sets. That support is narrower than it sounds. In hyperemesis gravidarum, the severe form that puts women in hospital, a Cochrane review found B6 shortened nothing, and the stay ran about three quarters of a day longer than on placebo. Head to head against ondansetron it came second, cutting nausea by 20 mm on a 100 mm scale against 51 mm, in a trial of 36 women.

Written from the evidence cards and the data on this page, then checked back against the sources. Bioma Learn has no human medical reviewer at this time and we say so rather than invent one. Information, not medical advice. How we verify.

Where to get it from food

• Acai berry drink, fortified fortified — 2.93 mg per 8 fl oz (172% DV)
• Chicken, broiler or fryers, breast, skinless, cooked — 1.6 mg per 1.0 piece (94% DV)
• Pistachio nuts, dry roasted — 1.38 mg per 1 cup (81% DV)
• Chicken, meatless fortified — 1.18 mg per 1 cup (69% DV)
• Sesame seeds, whole, dried — 1.14 mg per 1 cup (67% DV)

All vitamin B6 sources ranked →

Full guide: Vitamin B6: a water-soluble vitamin that can still damage nerves permanently