14.6: Vitamin B₆
- Page ID
- 57738
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Early in the 1950s, disturbing reports began to come in to the Food and Drug Administration (FDA). Here and there across the country, infants were developing a curious, unremitting irritability, with no apparent cause. There were odd muscle contractions. Some of the babies went into convulsions. All were receiving the same brand of infant formula.
Puzzling over this outbreak, nutritionists noted one clue. The formula was sold in two forms— one a canned liquid, the other a dry powder to be made into liquid formula by the mother. Only the babies on the canned formula seemed to be in trouble, and they became well as soon as the formula was replaced with some other.
A similar situation occurred again in 1982, just as quality control procedures stemming from the 1980 Infant Formula Act (requiring formulas to meet nutrient standards) were being adopted by the FDA.
What was wrong? An FDA scientist, recalling a study in which some young rats developed similar nerve and brain symptoms when fed diets very low in B6, correctly suspected a severe deficiency of vitamin B6 in the infant formula.
But why should this formula, based, like most, on cow’s milk, be so low in B6? It happened that the manufacturer had instituted what it believed to be a superior new way to sterilize the canned liquid formula. It used higher heat than usual, which destroyed the B6 in the liquid formula— not entirely, but enough to put babies, who were receiving little or no food other than the formula, in danger.
Vitamin B6 and Body Chemistry
Vitamin B6 is really a group of closely related chemicals. They are incorporated into coenzymes that play a part in a wide range of body chemistry, particularly in amino acid metabolism.
Its involvement with amino acid metabolism gives B6 a wide variety of jobs in body chemistry. It’s important in protein synthesis, because B6 coenzymes are used to make the “non-essential” amino acids by transferring the amino portion of one amino acid to the carbon skeleton of another. In fact, if it were not for this B6 coenzyme, 20, not 9, amino acids would be required in our diet.
The adult RDA of 1.3-1.7 mg/day of B6 takes into account our typically high protein intake.
The job of shuffling the amino portions of amino acids is also important when amino acids are used as fuel. Recall that for such use, the amino portions must be removed—a job calling for a B6 coenzyme. B6 coenzymes are also needed to convert the amino acid tryptophan into niacin, and to convert tryptophan into serotonin (a chemical messenger in the brain) (see Fig. 14-3).
Vitamin B6 shuttles the amino part (NH2) of amino acids.
The UL (Tolerable Upper Limit) for B6 is 100 mg/day. Doses of 2,000 mg or more taken for months can cause nerve damage, ranging from reversible numbness and weakness to severe and permanent damage.
