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Meer mensen dan gedacht hebben vitamine B6 tekort*
Uit een studie onder ruim 7.800 mensen blijkt dat een vitamine B6 tekort veel vaker voorkomt dan door gezondheidsinstellingen gedacht wordt. Al geruime tijd wordt dagelijkse hoeveelheden van 1-2 mg vitamine B6 geadviseerd, hoeveelheden die voldoende zouden moeten zijn om goede bloedwaarden (20 nmol/l) te handhaven. Nu blijkt dat voor bijna een kwart van alle onderzochte mensen en ook bij bepaalde groepen mensen deze geadviseerde waarden duidelijk te laag zijn. 75% van de vrouwen die een anticonceptiepil gebruiken hebben duidelijk een tekort, zo hebben alle vrouwen in de leeftijd van 13 tot 54 jaar een grotere kans op een tekort evenals alle 65 plussers. Mannen die roken hebben ook een veel hogere kans op een tekort. Vitamine B6 is belangrijk bij de aanmaak van neurotransmitters in de hersenen en tekorten geven zeker als er ook nog eens tekorten zijn aan omega-3 vetzuren aanleiding tot depressies en andere cognitieve stoornissen. Ook geven tekorten aanleiding tot het slecht functioneren van o.m. het calcium-, magnesium-, vitamine B3 en samen met foliumzuur en vitamine B12 het homocysteïne-metabolisme. Verder is vitamine B6 belangrijk tegen bloedarmoede, voor een goed immuunsysteem, een goed werkend hormoonsysteem. Moeheid is van meerdere aandoeningen een symptoom doch ook voor een tekort aan vitamine B6 evenals zweertjes of scheurtjes in de mondhoeken, zweertjes in de mond, een gezwollen rode tong en niet te vergeten een depressie. In dierlijke voeding zit vitamine B6 in een actieve vorm, PLP (pyridoxine-5-fosfaat) die door het lichaam het makkelijkst opgenomen wordt. Vitamine B6 uit plantaardige voeding moet in aanwezigheid van vitamine B2 door het lichaam eerst omgezet worden in de actieve vorm PLP. Veel vitamine B6 gaat verloren bij koken, malen, steriliseren en invriezen.

De conclusie van de onderzoekers is dat de dagelijks geadviseerde hoeveelheid eigenlijk 3-5 mg zou moeten zijn.
Large Scale Study Finds Vitamin B6 Deficiency Common in the U.S.
Researchers at Tufts University have discovered that vitamin B6 deficiency is much more common than previously thought. The National Institute of Health has long held that vitamin B6 deficiency is rare in the U.S. and in 1998 the Recommended Daily Allowance was set in a range, depending on age and gender from 1.3 mg to 2 mg daily.
For about 10 years now the RDA for Vitamin B6 has largely been assumed to be adequate to maintain plasma levels of B6 at 20 nmol/L in most people. The Tufts study has shown that instead, the RDA may be too low for at least four specific, large population groups.
Authors of the study note that this is the first of its kind to assess, on a large scale, the B6 (PLP) status of Americans. Their findings illustrate that one-size-fits-all nutrient recommendations are, in reality, inappropriate for millions of people.
In the Tufts study, published in the American Journal of Clinical Nutrition, researchers evaluated plasma levels of the most active form of B6, known as PLP (pyridoxal 5’ phosphate) in 7822 males and females, age one and older. Vitamin B6 occurs in six known forms but it is PLP that is the most biologically active form for human metabolism. PLP functions as a vital coenzyme in over 100 metabolic reactions, especially the metabolism of amino acids (proteins).
According to Martha Savaria Morris, PhD epidemiologist at the Jean Mayer USDA Human Research Center on Aging at Tufts University, “Across the study population, we noticed participants with inadequate vitamin B6 status even though they reported consuming more than the Recommended Daily Allowance of B6, which is less than 2 milligrams per day”. Researchers defined Vitamin B6 deficiency as plasma PLP concentration less than 20 nmol/L.
Four groups were found to have the highest prevalence of B6 deficiency including “women of reproductive age, especially current and former users of oral contraceptives, male smokers, non-Hispanic African American men, and men and women over age 65”. Although not singled out in this study, alcoholics are also at higher risk for vitamin B6 deficiency.
Researchers found that about 75% of women using oral contraceptives who did not take nutritional supplements were found to be deficient in PLP and that females age 13-54 had a much higher incidence of deficiency than males of the same age. Of the entire study population, 25% of those that did not take nutritional supplements and surprisingly 11% of those who take supplements were found to have PLP deficiency.
Implications of Vitamin B6 Deficiency
Neurological Abnormalities including depression and cognitive dysfunction
In its role as a vital coenzyme, B6 is involved in the synthesis of neurotransmitters including serotonin. B6 is required to form serotonin from the amino acid tryptophan. It is also required to synthesize dopamine, norepinephrine and GABA (gamma amino butyric acid). “Early symptoms of vitamin B6 deficiency include depression and confusion” according to Eleanor Noss Whitney and Sharon Rady Rolfes, authors of the text Understanding Nutrition.
Based on the findings of the Tufts study, that B6 deficiency is indeed widespread in the U.S., as is depression, shouldn't plasma B6 (PLP) be assessed in cases of depression and cognitive dysfunction prior to resorting to misused, prescription anti depressant drugs? Is B6 deficiency, along with other nutrient deficiencies like essential fatty acid omega 3, one more link to understanding the underlying causes of depression?
Anemia
PLP is required as a coenzyme in the synthesis of heme, a part of hemoglobin used to transport oxygen in blood. Without sufficient heme production hypochromic, microcytic anemia can develop with symptoms similar to iron deficiency anemia.
Impaired nutrient metabolism
A vitamin B6 deficiency is known to impair calcium and magnesium metabolism as well as the synthesis of niacin (B3) from tryptophan. Along with folic and B12 it works to regulate the metabolism of homocysteine. Elevated homocysteine levels are a known risk factor for heart disease. Vitamin B6 is also required to convert glycogen (the storage form of glucose) back into glucose, a function that the brain is very dependent on.
Steroid hormone function
PLP is an important hormone moderator on testosterone and estrogen cells because it binds to lysine on cell receptors and regulates the action of these hormones. Steroid hormone imbalance is linked to certain cancers including breast and prostate cancer.
Immune Function
A vitamin B6 deficiency decreases the production of lymphocytes, white blood cells responsible for antibody production. Decreased lymphocytes diminish our ability to fight the multitude of foreign invaders (antigens) that we are daily exposed to.
Signs of Vitamin B6 deficiency
Fatigue, a frequent symptom of many disorders, is a symptom of B6 deficiency. Other signs include cheilosis (sores or cracks at the corners of the mouth), glossitis (swollen red tongue) and stomatitis (inflammation of the mouth, oral ulcers). As mentioned earlier, the presence of depression, cognitive dysfunction and small cell type anemia (hypochromic, microcytic) are also suspect in a vitamin B6 deficiency.
Dietary sources of Vitamin B6
Bananas, potatoes, acorn squash, watermelon, avocados and prune juice are all good plant sources of vitamin B6. For example, one medium banana contains about .75 mg of B6. Light meat poultry including chicken breast and turkey are good animal sources. One 3 ounce serving of roasted chicken breast contains about .5 mg of B6.
Animal sources of B6 are higher in the most biologically active form of B6, PLP. Plant sources are higher in pyridoxine, which requires conversion to PLP for biological activity.
Cooking, milling, sterilization, and freezing all damage vitamin B6. That makes bananas, avocado and watermelon look like good dietary options for increasing daily intake of this very important nutrient.
Forms of B6 found in nutritional supplements
More often than not nutritional formulations include vitamin B6 in the form of pyridoxine hydrochloric acid. Pyridoxine requires adequate riboflavin (B2) for enzymatic conversion in the liver to the biologically active PLP form of B6. This illustrates the important synergistic effect that nutrients have on one another!
If you are trying to improve your vitamin B6 status, along with eating more foods high in vitamin B6, look for a nutritional supplement that contains vitamin B6 as pyridoxal 5’ phosphate, or PLP. In general, it is better to take the B family of vitamins as a complex, due to their synergistic affect on one another. The current safe upper limit dose, or UL is set at 100 mg/day. Sensory and peripheral neuropathies can develop at megadose levels.
The Tufts study dislodges the long held thinking that vitamin B6 deficiency is a rare condition. Dr. Morris and her team of researchers concluded that “Vitamin B-6 intakes of 3 to 4.9 mg/d appear consistent with the definition of a Recommended Dietary Allowance for most Americans. However, at that intake level, substantial proportions of some population subgroups may not meet accepted criteria for adequate vitamin B-6 status”.
Considering that vitamin B6 is involved in over 100 biochemical reactions, from neurotransmitter synthesis to glucose metabolism, there are at least 100 good reasons to prevent deficiency when possible and recognize and treat deficiencies that occur.
Sources:
Plasma pyridoxal 5'-phosphate in the U.S. population: the National Health and Nutrition Examination Survey, 2003–2004
Martha Savaria Morris, Mary Frances Picciano, Paul F Jacques and Jacob Selhub
From the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University and the National Institutes of Health Office of Dietary Supplements, Am J Clin Nutr 2008 87: 1446-1454. (Augustus 2008)