Vitamin B6. Reservoirs, receptors, and red-cell reactions

Vitamin B12 and vitamin B6 supplementation is needed among adults with phenylketonuria (PKU)

Phenylketonuria (PKU) is caused by an autosomal recessive deficiency of the enzyme phelnylalanine hydroxylase leading to a failure to convert phenylalanine to tyrosine. To avoid irreversible neurological damage because of increased phenylalanine, treatment is instituted rapidly after birth. We examined 31 adult PKU patients living on a less protein-restricted diet. Theoretically, these PKU patients had an increased risk of developing vitamin B(12) and B(6) deficiency because of a limited intake of animal products. Besides laboratory tests (n = 31) we obtained clinical information (n = 30) and detailed information on food consumption (n = 28). Three-quarters of the patients had early biochemical signs of vitamin B(12) deficiency. In spite of a normal folate status, 9 (29%) had a plasma homocysteine above 12 micromol/L. In accord with these findings, the food questionnaires indicated that 11 (39%) patients received less than the recommended daily vitamin B(12), and 20 (71%) received less vitamin B(6) than recommended. A significant association was found between reduced vitamin B(12) intake and both reduced serum cobalamins (p = 0.04) and reduced serum transcobalamin saturation (p = 0.03). Eleven patients took a vitamin pill daily, and these patients had a significantly lower plasma homocysteine compared to the rest. The present study suggests that adult PKU patients were at increased risk of developing vitamin B(12) deficiency, and their intake of vitamin B(6) was below the recommended daily intake. In conclusion PKU patients need continuing dietary guidance throughout adult life, and considering the risks, costs and potential benefits, daily vitamin supplementation seems justified in these patients.

Plasma vitamin B6 vitamers before and after oral vitamin B6 treatment: a randomized placebo-controlled study

BACKGROUND

Vitamin B(6) has attracted renewed interest because of its role in homocysteine metabolism and its possible relation to cardiovascular risk. We examined the plasma B(6) vitamers, pyridoxal 5'-phosphate (PLP), pyridoxal (PL), pyridoxine (PN), and 4-pyridoxic acid (4-PA) before and after vitamin B(6) supplementation.

METHODS

Patients (n = 90; age range, 38-80 years) undergoing coronary angiography (part of the homocysteine-lowering Western Norway B-Vitamin Intervention Trial) were allocated to the following daily oral treatment groups: (A), vitamin B(12) (0.4 mg), folic acid (0.8 mg), and vitamin B(6) (40 mg); (B), vitamin B(12) and folic acid; (C), vitamin B(6); or (D), placebo. EDTA blood was obtained before treatment and 3, 14, 28, and 84 days thereafter.

RESULTS

Before treatment, PLP (range, 5-111 nmol/L) and 4-PA (6-93 nmol/L) were the predominant B(6) vitamers identified in plasma. During the 84-day study period, the intraindividual variation (CV) in patients not treated with vitamin B(6) (groups B and D) was 45% for PLP and 67% for 4-PA. Three days after the start of treatment, the increases in concentration were approximately 10-, 50-, and 100-fold for PLP, 4-PA, and PL, respectively. No significant additional increase was observed at the later time points. The PLP concentration correlated to the concentrations of 4-PA and PL before treatment, but not after treatment. The PL concentration correlated with 4-PA before and after treatment.

CONCLUSIONS

Vitamin B(6) treatment has an immediate effect on the concentrations and the forms of B(6) vitamers present in plasma, and the changes remain the same during prolonged treatment. Our results suggest that the B(6) vitamers in plasma reflect vitamin B(6) intake.

Vitamin supplementation therapy in the elderly

Vitamin supplementation in large dosages is increasingly common in the older population. Often, such supplementation is used in an attempt to improve an individual's health status. There have been claims that the effects of vitamins halt the normal aging process or prevent and cure disease. However, several recent studies have failed to demonstrate the efficacy of vitamin supplementation in preventing several types of cancer. In moderate dosages, supplementation with vitamin E (tocopherols) shows promise as a lipid antioxidant, and may reduce the risk of coronary heart disease. However, before vitamin E becomes an accepted medical therapy, further long term studies must be undertaken to examine the safety and efficacy of such therapy. An adequate intake of vitamins should be ensured by adherence to a well balanced diet. However, the elderly are prone to circumstances that may prevent them from eating a balanced diet. In addition, there are several age-related medical conditions that may predispose individuals to dietary and vitamin deficiencies. To prevent vitamin deficiency diseases and their associated morbidity, modest vitamin supplementation may be necessary. However, supplementation should be reserved for individuals with documented deficiency or who are at risk of developing such deficiencies, especially those who are homebound or institutionalised. Vitamins taken in large dosages should be considered as drugs. These medicines, which are obtainable over-the-counter, should be carefully regulated to prevent toxicity.

Chronic exercise affects vitamin B-6 metabolism but not requirement of growing rats

The effect of chronic exercise (forced swimming) on vitamin B-6 status and metabolism was studied in growing male rats fed deficient (0 mg pyridoxine-HCl/kg), suboptimal (2 mg pyridoxine-HCl/kg) or control (7 mg pyridoxine-HCl/kg) diets for 9 wk. Sedentary rats were fed the same diets. Body weight gain was lower in deficient rats than in both other dietary groups. Sedentary rats were heavier than trained rats of all diet groups. Erythrocyte aspartate aminotransferase, urinary 4-pyridoxic acid excretion, blood (plasma and erythrocytes) and tissue B-6 vitamers were measured. Urinary 4-pyridoxic acid, plasma pyridoxal 5'-phosphate and erythrocyte aspartate aminotransferase values of exercised and sedentary rats responded to changes in dietary pyridoxine but were not different from one another. After 9 wk of vitamin B-6 depletion, tissue concentrations of pyridoxal 5'-phosphate and pyridoxamine 5;5'-phosphate were 41-66% and 26-49% lower, respectively, in the deficient groups than in the control groups. Larger percentage differences occurred in plasma than in tissues (95 vs. 22-66%). In liver, pyridoxal 5'-phosphate concentrations were lower, whereas pyridoxal concentrations were higher in trained than in sedentary rats. In gastrocnemius muscle, pyridoxal 5'-phosphate, pyridoxamine 5'-phosphate and total vitamin B-6 concentrations were higher in trained than in sedentary rats. Concentrations of vitamin B-6 compounds in heart, kidneys, brain and adrenals were not affected by training. On the basis of the vitamin B-6-dependent variables measured in this study, we conclude that prolonged exercise affects the metabolism of vitamin B-6, but does not increase the vitamin B-6 requirement in growing rats.

Abnormal vitamin B6 status in rheumatoid cachexia. Association with spontaneous tumor necrosis factor alpha production and markers of inflammation

OBJECTIVE

To compare vitamin B6 levels in rheumatoid arthritis (RA) patients and healthy control subjects.

METHODS

We measured levels of vitamin B6 in 23 adults with well-controlled RA, and in 23 healthy control subjects matched for age, sex, race, and weight.

RESULTS

Although plasma folate and vitamin B12 concentrations and erythrocyte B6 activity coefficients were similar in the patients and controls, plasma levels of pyridoxal-5'-phosphate (PLP) were lower in the RA patient group (mean +/- SD 46.1 +/- 48.1 versus 69.3 +/- 58.4 nmoles/liter; P < 0.004). In multivariate analyses, PLP was inversely associated with tumor necrosis factor alpha (TNF alpha) production by peripheral blood mononuclear cells (PBMC) (P < 0.001), after adjustment for age, pain score, erythrocyte sedimentation rate, and use of nonsteroidal antiinflammatory drugs.

CONCLUSION

PLP levels are reduced in patients with RA. This reduction is associated with TNF alpha production by PBMC.