Age differences in vitamin B6 status of 617 men

Factors influencing vitamin B6 status in domestic cats: age, disease, and body condition score

Limited studies are available on vitamin B6 status in domestic cats. To this end, we evaluated glutamate-oxaloacetate transaminase (GOT) activity in hemolysates with and without pyridoxal 5'-phosphate addition in two feline populations: a cohort of 60 healthy, domestic (sexually intact and specific pathogen-free) cats maintained under strictly controlled conditions with appropriate diets housed at the Feline Nutrition and Pet Care Center, and a cohort of 57 cats randomly selected between December 2022 to January 2023 that visited the Veterinary Medicine Teaching Hospital to seek care under different circumstances. The GOT activity expressed as the ratio with and without pyridoxal 5'-phosphate addition (primary activation ratio; PAR) decreased significantly with age in the healthy cohort. The PAR values normalized to age established a cut-off for vitamin B6 deficiency in both cohorts, identifying 17 of 101 animals as vitamin B6 deficient. Using machine learning, a partition-based model (decision tree) was built to identify the most important factors that predicted vitamin B6 deficiency while using the resulting tree to make predictions for new observations. This analysis, performed with all 101 cats, revealed that the diagnosis of an infectious, chronic or acute condition (0.55) was the main contributor, followed by age (0.26), and body condition score (optimal-overweight; 0.19). Thus, our study supports that vitamin B6 supplementation may be indicated in junior to adult animals diagnosed with an infectious, chronic, or acute conditions or healthy cats with body weight ranging from optimal to overweight. In older cats, even if healthy, underweight to optimal cats appear to be at risk of vitamin B6 deficiency.

Impact of lifestyle factors on dietary vitamin B6 intake and plasma pyridoxal 5'-phosphate level in UK adults: National Diet and Nutrition Survey Rolling Programme (NDNS) (2008-2017)

Reduction in dietary vitamin B6 intake is associated with an increased relative risk of diseases such as cancer, atherosclerosis and cognitive dysfunction. The current research has assessed vitamin B6 intakes and PLP concentrations as a marker of vitamin B6 status among the UK adult (≥ 19 years) population. This study was carried out using a cross-sectional analysis of the National Diet and Nutrition Survey Rolling Programme (NDNS) (2008-2017). The impacts of lifestyle factors, including type of diet, smoking, alcohol consumption, and commonly used medications grouped by therapeutic usage, were determined, and data were analysed using IBM SPSS®. Results are expressed as medians (25th-75th percentiles), with P values ≤ 0·05 considered statistically significant. Among UK adults, the median intakes of total population of dietary vitamin B6 met the reference nutrient intake and median plasma PLP concentrations were above the cut-off of vitamin B6 deficiency; however, we found an association between reduction in vitamin B6 intake and plasma PLP concentration and age group (P < 0·001). Smokers had significantly lower plasma PLP concentrations than non-smokers (P < 0·001). Moreover, regression analysis showed some commonly used medications were associated with plasma PLP levels reduction (P < 0·05). Taken together, we report on a tendency for dietary vitamin B6 intake and plasma PLP concentrations to decrease with age and lifestyle factors such as smoking and medication usage. This information could have important implications for smokers and in the elderly population using multiple medications (polypharmacy).

Association of development quotient with nutritional status of vitamins B6, B12, and folate in 6-59-month-old children: Results from the Brazilian National Survey on Child Nutrition (ENANI-2019)

BACKGROUND

Vitamins B6, B12, and folate are essential for the formation and maintenance of the human brain, but studies evaluating these vitamins with early childhood development (ECD) in children under five are limited and controversial.

OBJECTIVE

To evaluate the association between vitamins B6, B12, and folate concentrations/status and ECD.

METHODS

Data regarding 6,520 children aged 6-59 months (from the Brazilian National Survey on Child Nutrition [ENANI-2019]) were analyzed. ECD was assessed using the Survey of Well-being of Young Children's milestones questionnaire. Vitamin B6 concentration (nmol/L) was classified according to the tertile of the distribution and with the cutoff <20 nmol/L. Folate concentrations >45.3 nmol/L were classified as high, and vitamin B12 <150 pmol/L as deficient. The graded response model was used to estimate developmental age, and the developmental quotient (DQ) was calculated as the developmental age divided by chronological age. Multiple linear regression models were adjusted for confounders.

RESULTS

The DQ mean (95% confidence interval) for Brazilian children was 0.99 (0.97-1.01). Children aged 6-23 months (1.13 [1.10-1.16]) had a higher DQ mean than those aged 24-35 (0.99 [0.95-1.03]) and 36-59 months (0.89 [0.86-0.92]). Child age was inversely associated with DQ (β=-0.007; p<0.001). An interaction between child age and vitamin B12 deficiency in the DQ (β=-0.005; p<0.001) indicated that, in children aged 36-59 months, the DQ was markedly lower in children with B12 deficiency than in those without B12 deficiency. Vitamin B6 concentrations were directly associated with the DQ (β=0.0004; p=0.031) among children aged 24-59 months in the adjusted model. No association was observed between folate status and DQ.

CONCLUSIONS

In Brazil, the DQ is lower among older children, and those with vitamin B12 deficiency. Vitamin B6 status was directly associated with the DQ in children aged 24-59 months.

Circulating pyridoxal 5′-phosphate in serum and whole blood: implications for assessment of vitamin B6 status

Objectives

Concentrations of pyridoxal 5′-phosphate (PLP) in serum and whole blood are routinely measured. The suitability of these markers in capturing vitamin B6 insufficiency is not well studied.

Methods

In 212 subjects, concentrations of PLP and thiamine pyrophosphate (TPP) were simultaneously measured in EDTA-whole blood using Chromsystems® (52052) method on HPLC devices. The whole blood PLP concentrations were compared to serum PLP concentrations measured using reagents from Immundiagnostik® (KC 2100). The whole blood TPP concentrations measured with the Chromsystems® (52052) were compared to those measured by the Chromsystems® (35000) method. Concentrations of homocysteine (tHcy) and cystathionine (Cys) were measured and used to judge the PLP methods.

Results

Serum PLP concentrations were on average 41% lower than whole blood PLP [mean (SD)=55.4 (83.0) vs. 131 (217) nmol/L]. Serum and whole blood PLP showed a strong correlation [Pearson correlation coefficient=0.724, p<0.001, n=204]. Eighty-five samples showed discrepant results for PLP status (serum PLP ≤30 nmol/L, but whole blood PLP >51 nmol/L) while 102 samples showed coherent results (reference group). The discrepancy group showed higher odds ratio for elevated tHcy >12.0 μmol/L compared to the reference group [OR (95% confidence intervals, CI)=2.1 (1.2–4.0)]. The OR (95% CI) of elevated Cys >300 nmol/L was 1.9 (1.0–3.5) in the discrepancy group compared to the reference group. TPP concentrations were 6% lower when using the Chromsystems®, 52052 compared to levels measured with Chromsystems®, 35000.

Conclusions

Serum and whole blood PLP concentrations disagree in a substantial number of samples. Serum PLP was better in reflecting elevated tHcy and Cys compared to whole blood PLP. Whole blood PLP underestimates the prevalence of vitamin B6 insufficiency. Methods of measuring TPP concentrations in whole blood were exchangeable.

Association of Serum Pyridoxal Phosphate Levels with Established Status Epilepticus

BACKGROUND

The objective of this study was to determine the prevalence of pyridoxine deficiency, measured by pyridoxal phosphate (PLP) levels, in patients admitted to the hospital with established (benzodiazepine-resistant) status epilepticus (SE) (eSE) and to compare to three control groups: intensive care unit (ICU) patients without SE (ICU-noSE), non-ICU inpatients without SE (non-ICU), and outpatients with or without a history of epilepsy (outpatient).

METHODS

This retrospective cohort study was conducted at the University of North Carolina Hospitals and Yale New Haven Hospital. Participants included inpatients and outpatients who had serum PLP levels measured during clinical care between January 2018 and March 2021. The first PLP level obtained was categorized as normal (> 30 nmol/L), marginal (≤ 30 nmol/L), deficient (≤ 20 nmol/L), and severely deficient (≤ 5 nmol/L).

RESULTS

A total of 293 patients were included (52 eSE, 40 ICU-noSE, 44 non-ICU, and 157 outpatient). The median age was 55 (range 19-99) years. The median PLP level of the eSE group (12 nmol/L) was lower than that of the ICU-noSE (22 nmol/L, p = 0.003), non-ICU (16 nmol/L, p = 0.05), and outpatient groups (36 nmol/L, p < 0.001). Patients with eSE had a significantly higher prevalence of marginal and deficient PLP levels (90 and 80%, respectively) than patients in each of the other three groups (ICU-noSE: 70, 50%; non-ICU: 63, 54%; outpatient: 38, 21%). This significantly higher prevalence persisted after correcting for critical illness severity and timing of PLP level collection.

CONCLUSIONS

Our study confirms previous findings indicating a high prevalence of pyridoxine deficiency (as measured by serum PLP levels) in patients with eSE, including when using a more restricted definition of pyridoxine deficiency. Prevalence is higher in patients with eSE than in patients in all three control groups (ICU-noSE, non-ICU, and outpatient). Considering the role of pyridoxine, thus PLP, in the synthesis of γ-aminobutyric acid and its easy and safe administration, prospective studies on pyridoxine supplementation in patients with eSE are needed.

Vitamin B-6 and riboflavin, their metabolic interaction, and relationship with MTHFR genotype in adults aged 18-102 years

BACKGROUND

The generation of the active form of vitamin B-6, pyridoxal 5'-phosphate (PLP), in tissues is dependent upon riboflavin as flavin mononucleotide, but whether this interaction is important for maintaining vitamin B-6 status is unclear.

OBJECTIVE

To investigate vitamin B-6 and riboflavin status, their metabolic interaction, and relationship with methylenetetrahydrofolate reductase (MTHFR) genotype in adulthood.

METHODS

Data from 5612 adults aged 18-102 y were drawn from the Irish National Adult Nutrition Survey (NANS; population-based sample) and the Trinity-Ulster Department of Agriculture (TUDA) and Genovit cohorts (volunteer samples). Plasma PLP and erythrocyte glutathione reductase activation coefficient (EGRac), as a functional indicator of riboflavin, were determined.

RESULTS

Older (≥65 y) compared with younger (<65 y) adults had significantly lower PLP concentrations (P < 0.001). A stepwise decrease in plasma PLP was observed across riboflavin categories, from optimal (EGRac ≤1.26), to suboptimal (EGRac: 1.27-1.39), to deficient (EGRac ≥1.40) status, an effect most pronounced in older adults (mean ± SEM: 76.4 ± 0.9 vs 65.0 ± 1.1 vs 55.4 ± 1.2 nmol/L; P < 0.001). In individuals with the variant MTHFR 677TT genotype combined with riboflavin deficiency, compared with non-TT (CC/CT) genotype participants with sufficient riboflavin, we observed PLP concentrations of 52.1 ± 2.9 compared with 76.8 ±0.7 nmol/L (P < 0.001). In participants with available dietary data (i.e., NANS cohort, n = 936), PLP was associated with vitamin B-6 intake (nonstandardized regression coefficient β: 2.49; 95% CI 1.75, 3.24; P < 0.001), supplement use (β: 81.72; 95% CI: 66.01, 97.43; P < 0.001), fortified food (β: 12.49; 95% CI: 2.08, 22.91; P = 0.019), and EGRac (β: -65.81; 95% CI: -99.08, -32.54; P < 0.001), along with BMI (β: -1.81; 95% CI: -3.31, -0.30; P = 0.019).

CONCLUSIONS

These results are consistent with the known metabolic dependency of PLP on flavin mononucleotide (FMN) and suggest that riboflavin may be the limiting nutrient for maintaining vitamin B-6 status, particularly in individuals with the MTHFR 677TT genotype. Randomized trials are necessary to investigate the PLP response to riboflavin intervention within the dietary range. The TUDA study and the NANS are registered at www.ClinicalTrials.gov as NCT02664584 (27 January 2016) and NCT03374748 (15 December 2017), respectively.Clinical Trial Registry details: Trinity-Ulster-Department of Agriculture (TUDA) study, ClinicalTrials.gov no. NCT02664584 (January 27th 2016); National Adult Nutrition Survey (NANS), ClinicalTrials.gov no. NCT03374748 (December 15th 2017).

Associations of Vitamin B6 Intake and Plasma Pyridoxal 5'-Phosphate with Plasma Polyunsaturated Fatty Acids in US Older Adults: Findings from NHANES 2003-2004

Previous evidence suggests a potential dual impact of aging and vitamin B6 (B6) deficiency on polyunsaturated fatty acid (PUFA) metabolism; gender may influence PUFA biosynthesis. Perturbation of PUFA compositions during B6 deficiency could be linked to age-related health outcomes. However, little is known about the interrelationships between vitamin B6, PUFA, and gender in the older population. Therefore, we investigated whether gender-specific associations of B6 intake and plasma pyridoxal 5’-phosphate (PLP) concentration, respectively, with plasma PUFA concentrations and ratios (eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), arachidonic acid (AA), EPA + DHA, EPA/AA, and (EPA + DHA)/AA) existed in older adults. We further examined the relationships of adequate B6 status (PLP ≥ 20 nmol/L) with high (above median) plasma PUFA relative to deficient B6 status. This cross-sectional study analyzed 461 participants aged ≥60 years from NHANES 2003−2004. Nutrient intakes were assessed using two 24-h recalls and supplement questionnaires. PLP and PUFA concentrations were measured. Multivariate linear regression assessed the association of B6 intake and PLP with PUFA; multivariate logistic regression evaluated the relationship of adequate B6 status with high plasma PUFA, adjusting for demographic, socioeconomic, and dietary factors; physical activity; smoking; alcohol; medication; and BMI. There were interactions between gender and B6 intake on EPA (P-interaction = 0.008) and AA (P-interaction = 0.004) only, whereas no interaction existed between gender and PLP on PUFA. PLP was directly associated with EPA (β = 0.181, P = 0.002), DHA (β = 0.109, P = 0.005), EPA + DHA (β = 0.14, P = 0.002), EPA/AA (β = 0.186, P = 0.004), and (EPA + DHA)/AA (β = 0.13, P = 0.026). The odds of having high plasma EPA (adjusted (a) OR: 2.03, P = 0.049) and EPA/AA (aOR: 3.83, P < 0.0001) were greater in those with adequate B6 status compared to those with deficient B6 status. In conclusion, in US older adults, a higher PLP level was associated with a greater level of EPA, DHA, EPA + DHA, EPA/AA, and (EPA + DHA)/AA. Adequate B6 status was associated with high EPA and EPA/AA status. These findings suggest that sufficient vitamin B6 status may positively influence PUFA metabolism in older adults.

Determinants of Vitamin B6 Status in Community-Dwelling Older Adults: A Longitudinal Study Over a Period of 18 Years

BACKGROUND

Cross-sectional studies indicate an age-related decline in vitamin B6 status. Because longitudinal studies are lacking, the present study investigates the long-term association between age and vitamin B6 status in older adults by considering potential confounding factors.

METHODS

The study population consists of 249 women and 111 men aged ≥ 60 years, who had at least three follow-ups between 1996 and 2014 with complete data records on relevant parameters. Vitamin B6 status was assessed by serum pyridoxal 5'-phosphate (PLP) concentrations measured by high-performance liquid chromatography. Linear mixed models were used to analyze the influence of age, sex, body composition, supplements, diet, lifestyle, and serum creatinine on PLP concentrations.

RESULTS

At baseline, 37% of the subjects showed PLP concentrations < 30 nmol/L and more than half failed to meet the recommended dietary intake. Longitudinal analyses revealed that age, use of supplements and protein intake were positive determinants of PLP concentrations, whereas body fat showed a negative impact. No influence of sex, dietary vitamin B6 intake, lifestyle factors or serum creatinine on PLP concentrations was found.

CONCLUSION

The present study provides no evidence that in the course of aging PLP concentrations decline between 60 and 90 years. However, age-related changes in body composition, such as an increased ratio of fat mass to fat-free mass may negatively affect vitamin B6 status.

Revised D-A-CH Reference Values for the Intake of Vitamin B6

BACKGROUND

The Nutrition Societies of Germany, Austria, and Switzerland as the joint editors of the "D-A-CH reference values for nutrient intake" have revised the reference values for vitamin B6 in summer 2019.

SUMMARY

For women, the average requirement (AR) for vitamin B6 intake was derived on the basis of balance studies using a pyridoxal-5'-phosphate (PLP) plasma concentration of ≥30 nmol/L as a biomarker of an adequate vitamin B6 status. The recommended intake (RI) was derived considering a coefficient of variation of 10%. The RIs of vitamin B6 for men, children, and adolescents were extrapolated from the vitamin B6 requirement for women considering differences in body weight, an allometric exponent, growth factors as appropriate, and a coefficient of variation. For infants aged 0 to under 4 months, an estimated value was set based on the vitamin B6 intake via breast feeding. The reference value for infants aged 4 to under 12 months was extrapolated from the estimated value for infants under 4 months of age and the average vitamin B6 requirement for adults. The reference values for pregnant and lactating women consider the requirements for the foetus and the loss via breast milk. Key Messages: According to the combined analysis of 5 balance studies, the AR for vitamin B6 to ensure a plasma PLP concentration of ≥30 nmol/L is 1.2 mg/day for adult females and the extrapolated AR for adult males is 1.3 mg/day. The corresponding RIs of vitamin B6 are 1.4 mg/day for adult females and 1.6 mg/day for adult males, independent of age. For infants, the estimated value is 0.1 mg/day and 0.3 mg/day, depending on age. The AR of vitamin B6 for children and adolescents ranges between 0.5 and 1.5 mg/day, and the RI is between 0.6 mg/day and 1.6 mg/day. During pregnancy, the AR is 1.3 mg/day in the first trimester and 1.5 mg/day in the second and third trimesters; the RI is 1.5 mg/day in the first trimester and 1.8 mg/day in the second and third trimesters. For lactating women, the AR is 1.3 mg/day and the RI is 1.6 mg/day.

Seminal plasma vitamin B6 levels in men with asthenozoospermia and men with normal sperm motility, a measurement using liquid chromatography with tandem mass spectrometry

There is growing evidence that vitamin B₆ has a valuable contribution in maintaining normal sperm parameters; however, this contribution has not yet well-identified. Here, we aimed to measure the level of seminal plasma vitamin B₆ in men with asthenozoospermia compared to men with normal sperm motility. Ninety-seven human males with asthenozoospermia and eighty-eight human males with normal sperm motility (control) were recruited in this study. Collected semen samples were assessed for sperm motility, sperm count and semen volume. Liquid chromatography with tandem mass spectrometry was used to measure seminal plasma vitamin B₆ concentrations. A highly significant difference (p < .0001) in concentrations of seminal plasma vitamin B₆ was found between asthenozoospermic and control groups. Besides, no statistical correlations were found between seminal plasma vitamin B₆ level and sperm motility, sperm count, semen volume and men age in both tested groups. In conclusion, men with asthenozoospermia have lower seminal plasma vitamin B₆ level compared to men with normal sperm motility. Also, seminal plasma vitamin B₆ was found not to be correlated with sperm motility and count, semen volume and men age in both tested groups. These results may provide new contribution in the management of male infertility.

Tryptophan catabolites as metabolic markers of vitamin B-6 status evaluated in cohorts of healthy adults and cardiovascular patients

BACKGROUND

Vitamin B-6 status is routinely measured as pyridoxal 5'-phosphate (PLP) in plasma. Low concentrations of PLP are associated with rheumatic, cardiovascular, and neoplastic diseases. We have previously shown that vitamin B-6 status affects the kynurenine (Kyn) pathway of tryptophan (Trp) catabolism.

OBJECTIVE

This study aimed to comprehensively evaluate the use of Kyns as potential markers of functional vitamin B-6 status across 2 large cohorts.

METHODS

We measured circulating concentrations of the first 6 metabolites in the Trp catabolic pathway by LC-MS-MS in the community-based Hordaland Health Study (HUSK; n = 7017) and cardiovascular patient-based Western Norway Coronary Angiography Cohort (WECAC; n = 4161). Cross-sectional and longitudinal associations of plasma PLP with Kyns were estimated using linear and nonlinear regression-based methods.

RESULTS

3'-Hydroxykynurenine (HK), a substrate, and all 4 products formed directly by the PLP-dependent enzymes kynurenine transaminase and kynureninase contributed to the explanation of circulating PLP in multivariable-adjusted regression models. The construct HK:(kynurenic acid + xanthurenic acid + 3'-hydroxyanthranilic acid + anthranilic acid), termed HK ratio (HKr), was related to plasma PLP with standardized regression coefficients (95% CIs) of -0.47 (-0.49, -0.45) and -0.46 (-0.49, -0.43) in HUSK and WECAC, respectively. Across strata of cohort and sex, HKr was 1.3- to 2.7-fold more sensitive, but also 1.7- to 2.9-fold more specific to changes in PLP than a previously proposed marker, HK:xanthurenic acid. Notably, the association was strongest at PLP concentrations < ∼20 nmol/L, a recognized threshold for vitamin B-6 deficiency. Finally, PLP and HKr demonstrated highly sex-specific and corroborating associations with age.

CONCLUSIONS

The results demonstrate that by combining 5 metabolites in the Kyn pathway into a simple index, HKr, a sensitive and specific indicator of intracellular vitamin B-6 status is obtained. The data also underscore the merit of evaluating alterations in Kyn metabolism when investigating vitamin B-6 and health.

Dietary B Vitamin Intake Is Associated with Lower Urinary Monomethyl Arsenic and Oxidative Stress Marker 15-F2t-Isoprostane among New Hampshire Adults

Background: Arsenic exposure has been associated with an increased risk of cardiovascular disease (CVD). Growing evidence suggests that B vitamins facilitate arsenic metabolism and may protect against arsenic toxicity. However, to our knowledge, few studies have evaluated this in US populations.Objective: Our objective was to examine whether higher B vitamin intake is associated with enhanced arsenic metabolism and lower concentrations of preclinical markers of CVD among New Hampshire adults.Methods: We used weighted quantile sum (WQS) regression to evaluate the collective impact of 6 dietary B vitamins (thiamin, riboflavin, folate, niacin, and vitamins B-6 and B-12) on 1) the proportion of arsenic metabolites in urine and 2) 6 CVD-related markers [including urinary 15-F_2t-isoprostane (15-F_2t-IsoP)] among 418 participants (26-75 y of age) from the New Hampshire Health Study. Contributions of arsenic metabolites to B vitamin-CVD marker associations were also explored in structural equation models.Results: In WQS models, the weighted sum of B vitamin intakes from food sources was inversely associated with the proportion of monomethyl arsenic species in urine (uMMA) (β: -1.03; 95% CI: -1.91, -0.15; P = 0.02). Thiamin and vitamins B-6 and B-12 contributed the most to this association, whereas riboflavin had a negligible effect. Higher overall B vitamin intake was also inversely associated with 15-F_2t-IsoP (β: -0.21; 95% CI: -0.32, -0.11; P < 0.01), with equal contributions from the 6 B vitamins, which was partially explained by differences in the proportion of uMMA (indirect effect β: -0.01; 95% CI: -0.04, -0.00).Conclusions: Among New Hampshire adults, higher intakes of certain B vitamins (particularly thiamin and vitamins B-6 and B-12 from food sources) may reduce the proportion of uMMA, an intermediate of arsenic metabolism that has been associated with an increased risk of CVD. Higher overall B vitamin intake may also reduce urinary 15-F_2t-IsoP, a marker of oxidative stress and potential risk factor for CVD, in part by reducing the proportion of uMMA.

Pyridoxine improves hippocampal cognitive function via increases of serotonin turnover and tyrosine hydroxylase, and its association with CB1 cannabinoid receptor-interacting protein and the CB1 cannabinoid receptor pathway

BACKGROUND

In the present study, we investigated the effects of pyridoxine on hippocampal functions and changes in protein profiles based on the proteomic approach.

METHODS

Eight-week-old mice received intraperitoneal injections of physiological saline (vehicle) or 350mg/kg pyridoxine twice a day for 21days.

RESULTS

Phosphoglycerate mutase 1 was up-regulated, while CB1 cannabinoid receptor-interacting protein 1 (CRIP1) was down-regulated, in the pyridoxine-treated group. Additionally, the serotonin and tyrosine hydroxylase was increased in the hippocampus of the pyridoxine-treated group than in that of the vehicle-treated group. Furthermore, discrimination indices based on the novel object recognition test were significantly higher in the pyridoxine-treated group than in the vehicle-treated group. Administration of CRIP1a siRNA significantly increases the discrimination index as well as cell proliferation and neuroblast differentiation in the dentate gyrus. In addition, the administration of rimonabant, a CB1 cannabinoid receptor antagonist, for 3weeks significantly decreased the novel object recognition memory, the tyrosine hydroxylase level, the amount of cell proliferation, and neuroblast differentiation in the dentate gyrus. Treatment with pyridoxine significantly increased novel object recognition memory, but slightly ameliorated rimonabant-induced reduction in serotonin, the tyrosine hydroxylase level, the amount of cell proliferation, and neuroblast differentiation in the dentate gyrus.

CONCLUSION

These results suggest that pyridoxine promotes hippocampal functions by increasing serotonin and tyrosine hydroylase immunoreactivity in the hippocampus. This positive effect may be associated with CRIP1a and CB1 cannabinoid receptor function.

GENERAL SIGNIFICANCE

Vitamin-B₆ enhances hippocampal functions and this is closely associated with CRIP1a and CB1 cannabinoid receptors.

Direct and Functional Biomarkers of Vitamin B6 Status

Measures of B6 status are categorized as direct biomarkers and as functional biomarkers. Direct biomarkers measure B6 vitamers in plasma/serum, urine and erythrocytes, and among these plasma pyridoxal 5'-phosphate (PLP) is most commonly used. Functional biomarkers include erythrocyte transaminase activities and, more recently, plasma levels of metabolites involved in PLP-dependent reactions, such as the kynurenine pathway, one-carbon metabolism, transsulfuration (cystathionine), and glycine decarboxylation (serine and glycine). Vitamin B6 status is best assessed by using a combination of biomarkers because of the influence of potential confounders, such as inflammation, alkaline phosphatase activity, low serum albumin, renal function, and inorganic phosphate. Ratios between substrate-products pairs have recently been investigated as a strategy to attenuate such influence. These efforts have provided promising new markers such as the PAr index, the 3-hydroxykynurenine:xanthurenic acid ratio, and the oxoglutarate:glutamate ratio. Targeted metabolic profiling or untargeted metabolomics based on mass spectrometry allow the simultaneous quantification of a large number of metabolites, which are currently evaluated as functional biomarkers, using data reduction statistics.

Vitamin B6 status assessment in relation to dietary intake in high school students aged 16-18 years

The vitamin B6 status of high school students and its relationship with dietary intake were investigated in this cross-sectional study by face-to-face interview. A total of 157 healthy students aged 16-18 years (eighty-three boys and seventy-four girls) were randomly recruited from two out of nineteen senior high schools in Tainan, Taiwan. Vitamin B6 intakes were calculated from three 24-h dietary records. Direct and indirect vitamin B6 status indicators were measured in plasma, erythrocytes and urine. The anthropometric data, being similar to those of the first Nutrition and Health Survey in Taiwan (1993-1996), showed the normal growth and development of these students. All students except one girl (28.7 nmol/l) had plasma pyridoxal-5'-phosphate (PLP) levels >35 nmol/l, indicating an adequate vitamin B6 status. The mean dietary vitamin B6 intakes of boys and girls were 1.04 (sd 0.29) and 0.96 (sd 0.27) mg/d, respectively. Vitamin B6 status indicators, including plasma PLP, erythrocyte alanine aminotransferase activity coefficient (EALT-AC), aspartate aminotransferase activity coefficient (EAST-AC) and urinary 4-pyridoxic acid (4-PA), were correlated with vitamin B6 intake. Students with adequate values of plasma PLP (>35 nmol/l), EALT-AC ( < 1.25), EAST-AC ( < 1.8) and urinary 4-PA (>3.0 micromol/d) had median intakes of 1.08 and 1.01 mg/d, respectively, for boys and girls. This study suggests that vitamin B6 requirements for boys and girls aged 16-18 years were approximately 1.1 and 1.0 mg/d, respectively.

Plasma pyridoxal phosphate and pyridoxic acid and their relationship to plasma homocysteine in a representative sample of British men and women aged 65 years and over

Concentrations of pyridoxal phosphate and pyridoxic acid were measured in fasting plasma samples from British men and women aged 65 years and over, participating in a National Diet and Nutrition Survey during 1994–5, selected to be representative of the population of mainland Britain. In this population, the concentration of pyridoxal phosphate declined, whereas pyridoxic acid rose, with increasing age and frailty; however, both status indicators were strongly and directly (with a positive coefficient) correlated with estimates of vitamin B6intake. This was little affected by the inclusion of food energy and protein intakes in the model. Forty-eight percent of the participants living in the community and 75% of those living in institutions had plasma pyridoxal phosphate concentrations below a range considered normal from other studies. In a univariate regression model, plasma pyridoxal phosphate concentrations were inversely correlated with plasma homocysteine concentrations, consistent with the hypothesis that vitamin B6status may influence plasma homocysteine levels, and hence vascular disease risk. However, this relationship was partly attenuated in a multiple regression model including age, sex, domicile and biochemical status indices, including those of folate and vitamin B12. There was evidence that plasma pyridoxal phosphate was sensitive to metabolic conditions associated with inflammation and the acute-phase reaction, and that plasma pyridoxic acid was sensitive to renal function. Thus, neither index is an ideal predictor of vitamin B6status in older people, unless these confounding factors are allowed for. Since poor vitamin B6status may have health implications, e.g. for immune function, cognition, and for essential intermediary metabolic pathways in older people, it needs to be investigated as a possible public health problem.

Non-nutritional uses of vitamin B6

Vitamin B6is a water-soluble vitamin, and is readily metabolized and excreted, so it has generally been assumed to have negligible toxicity, although at very high levels of intake it can cause peripheral nerve damage. Nutritional deficiency disease is extremely rare, although a significant proportion of the population shows biochemical evidence of inadequate status, despite apparently adequate levels of intake. The vitamin has been used to treat a wide variety of conditions, which may or may not be related to inadequate intake. In some conditions use of vitamin B6supplements has been purely empirical; in other conditions there is a reasonable physiological or metabolic mechanism to explain why supplements of the vitamin many times greater than average requirements may have therapeutic uses. However, even in such conditions there is little evidence of efficacy from properly conducted controlled trials.

Vitamin status and cognitive function in a long-term care population

BACKGROUND

Ageing can be associated with poor dietary intake, reduced nutrient absorption, and less efficient utilization of nutrients. Loss of memory and related cognitive function are also common among older persons. This study aimed to measure the prevalence of inadequate vitamin status among long-term care patients and determine if an association exists between vitamin status and each of three variables; cognitive function, vitamin supplementation, and medications which alter gastric acid levels.

METHODS

Seventy-five patients in a long-term care hospital in Guelph, Ontario were recruited to a cross-sectional study. 47 were female and the mean age was 80.7 (+/-11.5) years, ranging from 48 to 100 years. Blood was used to measure levels of vitamins B12 (cobalamin), B6 (pyridoxal-5'-phosphate/PLP), erythrocyte folate, vitamin B3 (niacin) and homocysteine (Hcy). The Standardized Mini-Mental State Examination (SMMSE) was administered to measure cognitive function. A list of medications and vitamin supplementation for each patient was provided by the pharmacy.

RESULTS

The prevalence of low vitamin (B12, B6, erythrocyte folate, niacin) or high metabolite (homocysteine) levels among 75 patients were as follows: B12 <148 pmol/L in 5/75 (6.7%); B12 between 148 and 221 pmol/L in 26/75 (34.7%); B6 <or=30 nmol/L in 4/75 (5.3%); erythrocyte folate <370 nmol/L in 1/75 (1.3%); niacin ratio <or=1 in 20/75 (26.7%); homocysteine >13.3 micromol/L in 31/75 (41.3%). There was no significant difference among residents grouped into marked (n = 44), mild (n = 14), or normal (n = 9) cognitive function when evaluating the effect of vitamin status. There were no significant differences in mean B12 and homocysteine levels between users and non-users of drug therapy (Losec, Zantac, or Axid). Compared to vitamin supplement non-users, supplemented residents had significantly higher mean B12 (p < 0.0001) and erythrocyte folate (p < 0.05) concentrations and significantly lower mean homocysteine (p < 0.01) levels; 229.1 versus 423.6 pmol/L for B12, 882.9 versus 1043.6 nmol/L for erythrocyte folate and 14.4 versus 12.0 micromol/L for homocysteine.

CONCLUSION

Given the prevalence data on vitamin status in this sample population, the possible benefits of vitamin supplementation should be considered in clinical intervention studies using these populations of elderly.

The effect of vitamin B6 on cognition

BACKGROUND

Micronutrient status can affect cognitive function at all ages. Vitamin deficiencies could influence memory function and might contribute to age-associated cognitive impairment and dementia. Vitamin B6, comprising three chemically distinct compounds pyridoxal, pyridoxamine, and pyridoxine, is involved in the regulation of mental function and mood. Vitamin B6 is also an essential homocysteine re-methylation cofactor, and deficiency is associated with increase in blood homocysteine levels. Homocysteine is a risk factor for cerebrovascular disease and may also have directly toxic effects on neurons of the central nervous system. Neuropsychiatric disorders including seizures, migraine, chronic pain and depression have been linked to vitamin B6 deficiency. Epidemiological studies indicate that poor vitamin B6 status is common among older people. Hyperhomocysteinaemia has been suggested as a cause or mechanism in the development Alzheimer's disease and other forms of dementia. Supplementation with B vitamins including vitamin B6 has been shown to reduce blood homocysteine levels.

OBJECTIVES

To assess the efficacy of vitamin B6 supplementation in reducing the risk of developing cognitive impairment by older healthy people, or improving cognitive functioning of people with cognitive decline and dementia, whether or not vitamin B6 deficiency has been diagnosed.

SEARCH STRATEGY

The Specialized Register of the Cochrane Dementia and Cognitive Improvement Group was searched on 20 May 2003 using the terms: vitamin B6, pyridoxine, pyridoxamine, pyridoxal. For relevant trials on healthy elderly people MEDLINE, EMBASE and CENTRAL were searched using the previously mentioned terms as well as the term cognit *

SELECTION CRITERIA

All unconfounded, double-blind randomized controlled trials in which the intervention with vitamin B6 was compared with placebo for healthy older people or people with cognitive decline or dementia. The primary outcome of interest was the efficacy of vitamin B6 supplementation on cognitive function.

DATA COLLECTION AND ANALYSIS

The two reviewers independently evaluated all studies identified as possibly meeting the criteria for inclusion. One reviewer independently extracted the data. Studies were rated for their overall quality. The weighted mean differences between treatment and placebo groups, with 95% confidence intervals, were calculated for each outcome. Review Manager version 4.2 was used to analyse the variance.

MAIN RESULTS

No trials of vitamin B6 involving people with cognitive impairment or dementia were found. The two trials included in the review (Bryan 2002; Deijen 1992) used a double-blind, randomized, placebo-controlled design and involved 109 healthy older people. One trial restricted enrolment to women and the other to men. Vitamin B6 supplementation and healthy older women: Bryan 2002 enrolled 211 healthy women from various age groups into a 5-week study. The trial was of multifactorial design with folic acid, vitamin B12, vitamin B6 and placebo in its four arms. Twelve healthy women aged 65 to 92 years received 75 mg vitamin B6 orally per day and were compared with 21 healthy women who were allocated to placebo. No statistically significant benefits from vitamin B6 on mood or cognition were observed. Vitamin B6 supplementation and healthy older men: Deijen 1992 recruited 76 healthy men aged 70 to 79 years. They were divided into 38 matched pairs, one member of each pair randomly allocated to 20 mg of vitamin B6 (pyridoxine hydrochloride) per day for 12 weeks the other to placebo. No statistically significant differences between treatment and placebo were found in their effects on cognition or mood. Effect of vitamin B6 supplementation on vitamin B6 status: Deijen 1992 reported that 20 mg of pyridoxine hydrochloride per day for 12 weeks increased blood vitamin B6 activity as assessed as by plasma pyridoxal-5'-phosphate (WMD 238, 95%CI 211.58 to 264.42, P<0.00001) and erythrocyte enzyme asparate aminotransferase (WMD 0.43, 95%CI 0.30 to 0.56, P<0.00001). Effect of vitamin B6 supplementation on blood homocysteine concentration: Neither of the included trials measured homocysteine levels. Drop-outs: All participants allocated to vitamin B6 or placebo completed the trial protocol. Adverse Events: No adverse effects were reported. Effect of vitamin B6 on carer burden, care costs and institutionalization rate: We found no trials in which these outcomes were assessed.

REVIEWER'S CONCLUSIONS

This review found no evidence for short-term benefit from vitamin B6 in improving mood (depression, fatigue and tension symptoms) or cognitive functions. For the older people included in one of the two trials included in the review, oral vitamin B6 supplements improved biochemical indices of vitamin B6 status, but potential effects on blood homocysteine levels were not assessed in either study. This review found evidence that there is scope for increasing some biochemical indices of vitamin B6 status among older people. More randomized controlled trials are needed to explore possible benefits from vitamin B6 supplementation for healthy older people and those with cognitively impairment or dementia.

Plasma homocysteine concentrations of Indonesian children with inadequate and adequate vitamin B-6 status

The objective of the study was to determine the usefulness of utilizing plasma homocysteine concentrations as an indicator of vitamin B-6 status in subjects with inadequate and adequate status as demonstrated by currently accepted indicators. Plasma homocysteine concentrations of 77 third-grade Indonesian children (aged 8-9 y; boys and girls) were measured. About a quarter of these subjects had inadequate vitamin B-6 status as indicated by their plasma pyridoxal-5'-phosphate concentrations, erythrocyte alanine aminotransferase activity coefficients, and reported dietary vitamin B-6 intakes. No significant differences in plasma homocysteine concentrations were observed between subject groups shown to have inadequate and adequate vitamin B-6 status using currently accepted indicators. Plasma homocysteine concentrations of the subjects were not correlated with values for other vitamin B-6 indices. Plasma homocysteine concentration was not an indicator of vitamin B-6 status in these children, as it did not differentiate between children shown otherwise to have inadequate and adequate status of the vitamin.

An appraisal of vitamin B6 status indices and associated confounders, in young people aged 4-18 years and in people aged 65 years and over, in two national British surveys

OBJECTIVE

To compare vitamin B6 status indices with each other and with potential confounding factors, in the datasets from two national British surveys and associated studies.

DESIGN

Vitamin B6 status was measured by plasma pyridoxal phosphate (PLP) and plasma pyridoxic acid (PA) in both surveys, and also by erythrocyte aspartate aminotransferase activation coefficient (EAATAC) in one of the surveys. Plasma alpha1-antichymotrypsin was measured as an index of acute phase status; plasma creatinine was measured as an index of renal function; and plasma total alkaline phosphatase activity was measured as a proxy for PLP hydrolase activity.

SETTING

The survey of people aged 65 years and over was carried out in 80 postcode sectors across mainland Britain during 1994-95 and the survey of young people was carried out in 132 postcode sectors across mainland Britain during 1997.

SUBJECTS

Blood samples from c. 1,000 subjects of both sexes in each survey permitted measurements of plasma PLP and PA. There were also measurements of EAATAC in the young people's survey.

RESULTS

According to published limits of normality, only 5% or less of the young people had unacceptable vitamin B6 status as measured by plasma PLP. About half had apparently unacceptable status by EAATAC, but this observation is difficult to interpret. The young people had considerably higher plasma concentrations of PLP and lower concentrations of PA than the older people. In both surveys, plasma PLP was strongly correlated with plasma PA and in the young persons' survey it was also correlated, although much less strongly, with the basal activity and activation coefficient of aspartate aminotransferase. Both plasma PLP and EAATAC (but not PA nor basal aspartate aminotransferase activity) were influenced by acute phase status in young people, as indicated by significant correlations with alpha1-antichymotrypsin. In people aged 65 years and over, PA (but not PLP) was correlated with renal function, as indicated by its relation with plasma creatinine; however PLP (but not PA) was correlated with plasma alkaline phosphatase activity.

CONCLUSIONS

Several potential confounders - acute phase reaction, kidney malfunction and hydrolase activity - may influence vitamin B6 status indices, although differently for different indices and different age groups. Since older people have relatively poor vitamin B6 status, which may have important health implications for them, more reliable vitamin B6 status indices are needed.

Relationships between micronutrient intake and biochemical indicators of nutrient adequacy in a "free-living' elderly UK population

Nutritional assessments are frequently based on amounts of nutrients consumed. In the present paper the usefulness of nutrient intake data for assessing nutrient adequacy is examined in an elderly British population. Subjects were "free-living' elderly aged 68-90 years (sixty men, eighty-five women) in Norwich. Forty-two of forty-nine surviving males and sixty-seven of seventy-nine surviving females were reassessed after 2 years. With few exceptions, estimated micronutrient intake was not statistically predictive of biochemical measures of nutrient adequacy. Initial biochemical measures of nutritional adequacy were compared with those found 2 years later in an attempt to assess whether initial biochemical assessment was predictive of the "longer term' situation. Biochemical measurements at the start of the study were correlated to the same measurements made 2 years later for: serum ferritin, haemoglobin and erythrocyte count, whole-blood Se-glutathione peroxidase (EC 1.11.1.9; males only), plasma Cu, alkaline phosphatase (EC 3.1.3.1), ascorbic acid, vitamin B6 (pyridoxal-5-phosphate), folate and vitamin B12, total erythrocyte thiamin (males only), riboflavin (erythrocyte glutathione reductase (EC 1.6.4.1) activation coefficient): but not for: erythrocyte Cu-superoxide dismutase (EC 1.15.1.1) or plasma Zn. Either only small changes, or no changes, in mean values were seen over the 2 years for most of the biochemical measures. One exception was a large increase in plasma folate. The only important "negative' features seen at 2-year follow up were a large fall in serum ferritin concentration and a large increase in the activity of two antioxidant defence enzymes, superoxide dismutase and glutathione peroxidase. As judged by currently accepted biochemical deficiency threshold values, a small proportion of subjects were possibly at risk of Fe (3% men; 1% women), folate (7%, 3%), thiamin (12%; 3%) and vitamin C (15%; 17%) deficiency. Many more appeared to be at risk of vitamin B6 (42%; 47%) and riboflavin (77%; 79%) deficiency. It was concluded that the requirements of the elderly for vitamins B1, B2 and C, and the biochemical deficiency threshold values used to indicate vitamin B6 deficiency, need review.

Nutrient intake and biochemical status of non-instutionalized elderly subjects in Norwich: comparison with younger adults and adolescents from the same general community

The Department of Health (1992) has recently stated that 'Nutritional reviews concerning elderly people are especially constrained by lack of data', and that much of the emphasis in the nutritional literature has been placed on the study of institutionalized, and often chronically ill, elderly subjects rather than the non-institutionalized elderly who form the majority of this population. The present study presents information on the dietary intake and biochemical status of non-institutionalized elderly subjects (68-73 and 74-90 years) and compares such data with those obtained for adult (20-64 years) and adolescent (13-14 years) populations living within the same community. Nutrient intakes and appropriate biochemical measurements of nutrient status, performed on fasting blood samples, were statistically examined and have been discussed in relation to potential age-related influences. The nutrient intake of elderly subjects was on a par with adolescents of corresponding sex but generally lower than that of adult counterparts. There were several significant differences in biochemical measurements of nutrient status between age groups. In general these did not suggest progressive age-related trends. However, there were significant suggestions of age-related increases in whole-blood glutathione peroxidase (EC 1.11.1.9) activity, serum ferritin, plasma cholesterol, LDL and triacylglycerol concentrations and decreases in plasma HDL and ascorbic acid concentrations. The significance of these differences is discussed. An age-related difference (suggestive of a decline) in vitamin C status together with a difference (suggestive of an increase) in glutathione peroxidase activity may indicate an imbalance in the regulation of O2-derived free-radicals with ageing. These observations are worthy of a further study in the light of current thinking which relates the induction of a number of diseases to oxidative damage.

Hip fracture patients may be vitamin B6 deficient. Controlled study of serum pyridoxal-5'-phosphate

Deficiency of vitamin B6 in rats may result in defective bone formation, possibly due to decreased activity of the enzyme ornithine decarboxylase which requires pyridoxal-5'-phosphate (PLP) as a co-factor and is responsible for production of intracellular putrescine, a metabolic regulator. We studied 3 groups of patients (62 fit ambulant out-patients, 21 elective arthroplasty patients, and 20 hip fracture patients) and assayed their PLP status by high performance liquid chromatography. The reference range derived from the out-patients was 13-106 nmol/L. 3 of the arthroplasty group and 10 of the fracture group had serum PLP concentrations less than 13 nmol/L (P < 0.01). We conclude that PLP may be an etiologic factor in hip fracture by virtue of its role in the activity of a key regulatory protein.

Vitamin B-6 supplementation in elderly men: effects on mood, memory, performance and mental effort

This study evaluates the effects of vitamin B-6 supplementation (20 mg pyridoxine HCL daily for 3 months) on mood and performance in 38 self-supporting healthy men, aged between 70-79 years. Effects were compared with 38 controls who received placebo and were matched for age, plasma pyridoxal-5'-phosphate (PLP) concentration and intelligence score. Before and after drug intervention vitamin B-6 status was determined, and mood and performance were measured by means of a computerized testing system. In addition, the phasic pupil response was measured in order to assess mental effort. Positive effects of vitamin B-6 supplementation were only found with respect to memory, especially concerning long-term memory. In view of the finding that mental performance improvement and delta PLP values were most strongly correlated within an intermediate range of delta PLP, it is suggested that cognitive effects are primarily associated with a certain range of vitamin B-6 status increment. The general conclusion is that vitamin B-6 supplementation improves storage of information modestly but significantly.

Plasma B-6 vitamer and plasma and urinary 4-pyridoxic acid concentrations in young women as determined using high performance liquid chromatography

Plasma B-6 vitamer and plasma and urinary 4-pyridoxic acid concentrations of 21 young white women, 21-27 years, having radiomonitored pyridoxal 5'-phosphate and coenzyme stimulation of erythrocyte alanine aminotransferase activities indicative of adequate vitamin B-6 status were determined in an effort to establish normal ranges for plasma B-6 vitamers. B-6 vitamers and 4-pyridoxic acid were quantitated using reversed phase high performance liquid chromatography with fluorometric and ultraviolet detection. Pyridoxal phosphate values obtained by radioenzymatic and chromatographic, fluorometric and ultraviolet, assays were highly correlated as were pyridoxine phosphate values determined using both detectors. The B-6 vitamer and 4-pyridoxic acid values of these subjects should be of use in the establishment of normal ranges of these congeners in women.

Plasma B6 vitamer and plasma and urinary 4-pyridoxic acid concentrations of middle-aged obese black women

Plasma B6 vitamer and plasma and urinary 4-pyridoxic acid (4-PA) concentrations of fifteen middle-aged obese black women were determined by high-performance liquid chromatography (HPLC). Estimated protein and vitamin B6 intakes of the subjects, aged 27-52 years, were 64.5 +/- 15.6 g and 1.21 +/- 0.68 mg (mean +/- S.D.), respectively. Mean HPLC-derived plasma B6 vitamer and 4-PA concentrations for these subjects were 68.9, 3.1, 1.2, 4.1, 3.4, 7.2 and 2.0 nmol/l for pyridoxal 5'-phosphate (PLP), pyridoxine 5'-phosphate, pyridoxamine 5'-phosphate, pyridoxal, pyridoxine, pyridoxamine and 4-PA, respectively. The mean urinary 4-PA/creatinine ratio of the women was 0.88 mumol/mmol. All subjects had plasma PLP levels indicative of adequate vitamin B6 status. Vitamin B6 status parameters of the middle-aged obese black women were similar to those previously reported for white nonobese women having adequate vitamin B6 status.

Separation and quantification of the B6 vitamers in plasma and 4-pyridoxic acid in urine of adolescent girls by reversed-phase high-performance liquid chromatography

The vitamin B6 status of seemingly healthy adolescent girls was determined using several accepted and proposed parameters in an effort to establish guidelines for status evaluation. High-performance liquid chromatography-derived plasma B6 vitamers (pyridoxal phosphate, PLP; pyridoxine phosphate. PNP; pyridoxamine phosphate, PMP; pyridoxal, PL; pyridoxine, PN; and pyridoxamine, PM) and 4-pyridoxic acid (4-PA) concentrations and urinary 4-PA levels of 28 white adolescent females, 12-15 years, having radiomonitored plasma PLP concentrations and coenzyme stimulation of erythrocyte alanine aminotransferase activities indicative of adequate status were determined. Mean vitamin B6 and protein intakes were 1.48 mg and 78.3 g. Ranges for plasma B6 vitamer and 4-PA concentrations (nmol/l) were: PLP, 40.9-122.2; PNP, non-detectable (ND)-16.1; PMP, ND-8.1; PL, ND-15; PN, ND-21.9; PM, ND-17.8; and 4-PA, ND-55.7. PLP was the only vitamer found in plasma of all subjects. Urinary 4-PA concentrations ranged from 0.11 to 2.50 mumol/mmol of creatinine. B6 vitamer values of these girls should be of use in the establishment of normal ranges for vitamin B6 status parameters.

Pyridoxal-5'-phosphate and pyridoxal biokinetics in aging Wistar rats

Biokinetic parameters of plasma pyridoxal-5'-phosphate (PLP) and pyridoxal (PL) disposition were studied in male Wistar rats aged 8 and 27 months kept from weaning on a purified diet containing 250 g casein and 6 mg pyridoxine.HCl per kg. Baseline plasma PLP concentration was lower in the older animals (514 +/- 56 nmol/L for young and 317 +/- 124 nmol/L for old animals), whereas baseline plasma PL concentration did not differ between age groups (average 235 nmol/L for both young and old animals). We hypothesized lower baseline plasma PLP in the older animals was caused by an increased PLP elimination rate, a decreased PLP synthesis rate, or a combination of these processes. Observations from earlier in vitro experiments suggest age-related changes occur in vitamin B-6 metabolizing enzyme activities. In the in vivo experiments described here no age-related difference in plasma PLP elimination rate nor in plasma PLP synthesis rate was observed to explain the observed decrease in plasma PLP concentration with age.

Low vitamin B6 status in patients with acute myocardial infarction

The vitamin B6 status of 84 patients with acute myocardial infarction was compared with that of 84 control subjects. Pyridoxal and pyridoxal 5'-phosphate (PLP) in plasma and erythrocytes, as well as the basal and total potential activity of the PLP-dependent enzyme aspartate aminotransferase in erythrocytes, were measured for a comprehensive assessment of vitamin B6 status. The mean levels of all vitamin B6 indexes (except pyridoxal) were lower in the patients than in the control subjects. The differences were statistically significant, except for erythrocyte PLP and total potential enzyme activity. The adjusted relative odds of a myocardial infarction for subjects in the lowest quartile of plasma PLP was about 5 times higher when compared with those in the highest quartile (relative odds = 5.2, 95% confidence interval = 1.4 to 18.9). Similar findings were found with the other vitamin B6 indexes. No significant association between infarct size, as estimated by creatine kinase level, and the vitamin B6 indexes was observed.

Plasma B6 vitamer and 4-pyridoxic acid concentrations of men fed controlled diets

A rapid and sensitive procedure is described for the analysis of all the B6 vitamers and 4-pyridoxic acid in human plasma utilizing reversed-phase high-performance liquid chromatography with ultraviolet and fluorometric detection. Pyridoxal phosphate values obtained by radiometric and chromatographic, ultraviolet and fluorometric, assays were highly correlated as were pyridoxine phosphate values determined using both detectors. Plasma B6 vitamer and 4-pyridoxic acid concentrations of 22 men fed diets containing 0.75-0.98 mg of vitamin B6 daily for eight weeks were in the range of reported values; pyridoxal phosphate was their predominant plasma B6 vitamer. This methodology should be useful in the assessment of vitamin B6 requirements.