[mdavid626]

> Cases of toxicity have been reported at doses as low as 21 mg per day, the recommended daily intake is 1.3 to 2 mg. The person in question was diagnosed with issues possibly caused by this after 2 years.

That's very hard to believe. In my "normal" vitamin B-Complex supplement there is 20mg of B6 in the daily dose. If 21mg per day would cause nerve damage, that we'd know (and it would be an epidemic).

[jefozabuss]

I've been taking "Opti-Men" from Optimum Nutrition for like 10 years now and it seems to have 50mg in a (full) serving that I take.

Since B6 is water soluble doesn't it mean most of it might just leave our body if not needed? (No storage in fat)

[richarlidad]

This is the mechanism of action:

Vitamin B6 is an antioxidant and coenzyme involved in amino acid, carbohydrate and lipid metabolism. Humans cannot directly produce active vitamin B6 (pyrixodal phosphate). However, salvage pathways allow the enzymatic conversion of vitamin B6 vitamers, including pyridoxine, pyridoxal and pyridoxamine by the enzyme pyridoxal kinase, into active vitamin B6.

In the body, active vitamin B6 is involved in metabolic reactions including GABA synthesis, monoamine neurotransmitter metabolism, the metabolism of polyunsaturated fatty acids and phospholipids, amino acid metabolism and the conversion of tryptophan to niacin.

Vitamin B6 reduces homocysteine levels by acting as a coenzyme for both cystathionine-beta-synthase (CBS) and cystathionine-gamma-lyase (CSE) in the transsulfuration pathway following a postprandial methionine-load (after a meal). In the fasting state, homocysteine is primarily metabolised via the remethylation pathway which does not require vitamin B6.

In the transsulfuration pathway, homocysteine is converted to cystathionine by CBS, then to cysteine by CSE. During moderate vitamin B6 deficiency, CSE exhibits much greater loss of activity compared to CBS. However cysteine production is preserved due to an accumulation of cellular and plasma cystathionine in a larger substrate pool which compensates for reduced CSE activity. As CBS is a vitamin B6-dependent enzyme, CBS deficiency (typically genetic causes) can result in elevated fasting and post-methionine load homocysteine due to impaired synthesis of cystathionine from homocysteine. Elevated homocysteine levels increase oxidative stress, may inhibit nitric oxide synthesis, increase vascular endothelial cell damage and accelerate low-density lipoprotein (LDL) deposition in arteries.

Vitamin B6 may significantly decrease the rate of formation of kidney stones in patients with type I primary hyperoxaluria, a condition caused by a deficiency of the liver-specific enzyme alanine-glyoxylate:aminotransferase by reducing levels of urinary oxalate. The protective effect of vitamin B6 supplementation for kidney stones appears to only occur in women (-34% risk) and not men.

[mdavid626]

Can you boil this down for us? Does or does not B6 accumulate in the body?

[richarlidad]

Even though it is water soluble, yes it can accumulate, especially at the higher doses found in supplements. The primary way this happens is via unaware supplementation. Usually people are unaware that their product contains b6 - it's in a lot of products that are not advertised to contain it.

So even though it is water soluble it can still accumulate when taken at these high doses. Most supplements contain pyridoxine, which can acumulate and damage peripheral nerves. Indeed the form of B6 is important, and manufacturers take advantage of the fact that consumers (and medical practitioners) are unaware of the difference. Taking P-5-P may be less risky than pyridoxine hydrochloride, a cheaper option that is included in most supplements.

[mdavid626]

I agree, as B6 is water soluble, it should be fine to take more, the body just gets rid of it.

[LightHugger]

the eu set 12mg as an absolute upper limit on what's safe.

I'm curious, do you exercise every day? b6 seems to get flushed out of the body in proportion to how much exercise you get, as it gets released by the muscles and then only partially reabsorbed with each cycle. It's possible what you're taking would cause you nerve damage if you were sedentary.

[hollerith]

If the situation was that everyone in the world could take 20 mg per day without problems, but then 21 mg per day would reliably cause irreversible damage, then yes as a society we would be very clear by now on the dangers of taking too much B6.

The actual situation is probably that most people can take 2 or 3 times 20 mg per day (and some people can take 10 times 20) without problems. There is a lot of variance in the gut absorption and the rate of metabolism of a lot of micronutrients in the human body.