Sunday, July 19, 2009

Different types of vitamin B6 and why it matters

People who have a reasonable grasp of vitamins know that they come in different forms. I would suspect that they widest know example is synthetic vitamin E and natural vitamin E, if you are not familiar with this see this article for an introduction.

However most people, me included, don't really know how complex this issue really is. This blog post will hopefully help you understand of the issues around vitamin B6.

If you google Vitamin B6 you will quickly find out that its chemical name is pyrodoxine. Dig a little deeper and you will find that it goes by three different names:

Structure of <span class= Structure of <span class= Structure of <span class=

Pyridoxine (PN)

Pyridoxal (PL)

Pyridoxamine (PM)

Picture credits

A close look at the three mentioned vitamin B6 pictures, they all look the same except for the letters that are at the very top of the diagram. What happens is the building block of vitamin B6 is the lower part (the same part on each diagram) this is the essential vitamin B6. Now the body takes the above mentioned molecules and from them creates the molecule that your body needs. This is shown below. You can see the vitamin B6 molecule like above, but it has a cluster (a Phosphate group, hence the name) to the right.

Structure of <span class=

Pyridoxal Phosphate (PNP)

Thus there are four different types of molecules that contain the essential part of Vitamin B6.

There are at least three other types. PLP and PMP which unsurprisingly have the same group of chemicals on the side of them as PNP, but instead of having this group on a PN molecule they have it on a PL or PM molecule. The other type is called PA. This is appears in urine when other types of vitamin B6's are broken down for removal from the body.

So what set this blog post off? An article I was reading. It looked at PN-glucosid which is yet another type of vitamin B6. And as you would expect it is a PN molecule that instead of being attached to a phosphate group like PNP it is attached to a glucoside, which is a glucose molecule with a fatty tail.

The study investigated how much of this PN-glucoside was in various foods, and how the body absorbed/used it.

What the study found was that there was no PN-glucoside in breast milk, or cow's milk. This is important because breast milk and untreated cows milk have what baby and calf need, More importantly the body and cow tend not to put in things into the milk that are not useful. Therefore the complete lack of PN-glucoside tells you that babies and calves don't need or can't use PB-glucoside. This points to PB-glucoside not biologically active in people. The study said it like this:
"It was particularly noteworthy that PN-glucoside was not detected in any of the human milk samples, regardless of the diet of the donor."
The study found that in their plant based samples: broccoli, peanut butter, raw green beans, raw carrots, orange juice had 35-80% of there vitamin B6 as PN-glucoside. They went on to say:
"Most information concerning the content of of vitamin B6 in foods has been derived by microbiological growth assays using vitamin B6 dependant yeasts"
This is very disturbing as the standard method for determining the vitamin B6 involves a process that would remove the glucoisde and turn the PN-glucoside to just PN. Thus
"Microbiological assay procedures such as these would overestimate the biologically available vitamin B6 in foods"
and
"The high concentration of PN-glucoside in many plant derived foods suggest a widespread incomplete bio availability of the vitamin in human diets, which could not be evaluated accurately by current food composition tables."
Thus this means all food tables constructed up to this point could well be out by 35-80%. To me that level of variance makes the food table somewhat redundant.

This study was published in 1987. Since then there has been massive jump in analytical techniques. The computer has revolutionized laboratory work. So in the last 20 years have the food tables been completely rewritten? No not from my knowledge. I cannot find any evidence that vitamin
B6 food tables were all reanalyzed in light of this rather fundamental issue.

Further more 10 years later in 1997 a paper was published that looked at the same issue with radioactive PN and PN-glucoside. Not only was the PN-glucoside not biologically active (eg not able to be used by the body) They found that the PN-glucoside was even blocking the uptake of PN. So this gets even more complex and indicates further that when it comes to vitamin
B6, the food levels of this vitamin are even less accurate.

Article reference: Gregory & Ink.
Identification and quantification of pyridoxine .beta.-glucoside as a major form of vitamin B6 in plant-derived foods J. Agric. Food Chem., 1987, 35 (1), pp 76–82

3 comments:

  1. Thank you for sharing this! Perhaps I'm missing it, but can you tell me which form of vitamin B6 we should be seeking?

    Thank you!

    ReplyDelete
  2. Aaron

    That is a very good question, one I should have answered in the posting. To be honest I don't yet know the answer! As soon as I figure out more will post about it.

    ReplyDelete
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