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

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.

Vitamin B6: a scoping review for Nordic Nutrition Recommendations 2023

Pyridoxal 5´-phosphate (PLP) is the main form of vitamin B6 in animal tissue and functions as a coenzyme for more than 160 different enzymatic reactions in the metabolism of amino acids, carbohydrates, lipids, and neurotransmitters. Estimated dietary intake of vitamin B6 and plasma PLP values differ a lot between studies, something which may be due to variable use of supplements, variations in dietary assessment and analytical methods. These factors make it difficult to achieve precise data for setting a correct recommended intake of vitamin B6. In addition, a plasma PLP concentration of 30 nmol/L is considered to be sufficient and the current recommendations for vitamin B6 intake is based on this concept. However, the metabolic marker for vitamin B6 status, HK ratio (HKr), starts to increase already when plasma PLP falls below 100 nmol/L and increases more steeply below 50 nmol/L, indicating biochemical deficiency. Consequently, a plasma PLP concentration of 30 nmol/L, may be too low as a marker for an adequate vitamin B6 status.

A Novel Two-Dimensional Liquid Chromatography Combined with Ultraviolet Detection Method for Quantitative Determination of Pyridoxal 5'-Phosphate, 4-Pyridoxine Acid and Pyridoxal in Animal Plasma

Vitamin B₆ is an indispensable micronutrient in organisms and is widely distributed in blood, tissues, and organs. Changes in the content and ratio of vitamin B6 can affect the entire physiological condition of the body, so it becomes particularly important to reveal the relationship between changes in its content and disease by monitoring vitamin B6 levels in the organism. In this study, a two-dimensional liquid chromatography-UV detector (2D-LC-UV) was used to establish a method for the simultaneous detection of PLP, PA, and PL for the first time. First, PLP, PA, and PL were extracted with plasma: 0.6 M TCA: ultrapure water = 1:2:3 (v/v/v) and then derivatized. Enrichment and preliminary separation were performed on a one-dimensional column and automatically entered into a two-dimensional column for further separation. This method exhibited good selectivity, and the correlation coefficients for the analyte calibration curves were >0.99. The detection limits for PLP, PA, and PL were 0.1, 0.2, and 4 nmol/L, respectively. The results showed that the system has high loading capacity, excellent resolution, and a good peak shape. This method is expected to provide applicability for the determination of PLP, PA, and PL in pharmacological, pharmaceutical, and clinical research.

Analysis of the Impact of Selected Vitamins Deficiencies on the Risk of Disability in Older People

Vitamin deficiencies have a serious impact on healthy aging in older people. Many age-related disorders have a direct or indirect impact on nutrition, both in terms of nutrient assimilation and food access, which may result in vitamin deficiencies and may lead to or worsen disabilities. Frailty is characterized by reduced functional abilities, with a key role of malnutrition in its pathogenesis. Aging is associated with various changes in body composition that lead to sarcopenia. Frailty, aging, and sarcopenia all favor malnutrition, and poor nutritional status is a major cause of geriatric morbidity and mortality. In the present narrative review, we focused on vitamins with a significant risk of deficiency in high-income countries: D, C, and B (B6/B9/B12). We also focused on vitamin E as the main lipophilic antioxidant, synergistic to vitamin C. We first discuss the role and needs of these vitamins, the prevalence of deficiencies, and their causes and consequences. We then look at how these vitamins are involved in the biological pathways associated with sarcopenia and frailty. Lastly, we discuss the critical early diagnosis and management of these deficiencies and summarize potential ways of screening malnutrition. A focused nutritional approach might improve the diagnosis of nutritional deficiencies and the initiation of appropriate clinical interventions for reducing the risk of frailty. Further comprehensive research programs on nutritional interventions are needed, with a view to lowering deficiencies in older people and thus decreasing the risk of frailty and sarcopenia.

Riboflavin Is an Important Determinant of Vitamin B-6 Status in Healthy Adults

BACKGROUND

Riboflavin is required to generate the active form of vitamin B-6 (pyridoxal 5'-phosphate; PLP) in tissues, but the relevance of this metabolic interaction for nutritional status of vitamin B-6 is unclear because riboflavin biomarkers are rarely measured in human studies.

OBJECTIVES

The purpose of this study was to identify the determinants of biomarkers of vitamin B-6 and riboflavin status and to examine the relationship between these nutrients in healthy adults.

METHODS

Multiple linear regression was performed on observational data in 407 healthy adults aged 18-92 y who did not use B-vitamin supplements. Vitamin B-6 status was assessed by plasma PLP concentrations and erythrocyte glutathione reductase activation coefficient (EGRac) was used as a functional indicator of riboflavin status.

RESULTS

Dietary intakes of vitamin B-6 and riboflavin were below the average requirements in 10% and 29% of participants, respectively. Suboptimal status of vitamin B-6 (PLP ≤30.0 nmol/L) was more prevalent in adults aged ≥60 y than in younger participants (i.e., 14% compared with 5%), whereas a high proportion (i.e., overall 37%) of both age groups had deficient riboflavin status (EGRac ≥1.40). In multiple regression analysis, EGRac (P = 0.019) was a significant determinant of plasma PLP, along with dietary vitamin B-6 intake (P = 0.003), age (P < 0.001), BMI (kg/m2) (P = 0.031), and methylenetetrahydrofolate reductase gene (MTHFR) genotype (P < 0.001). Significant determinants of EGRac were dietary riboflavin intake (P < 0.001), age (P < 0.001) and MTHFR genotype (P = 0.020). Plasma PLP showed a stepwise decrease across riboflavin status categories from optimal (EGRac ≤1.26) to low (EGRac 1.27-1.39) to deficient status (P = 0.001), independent of dietary vitamin B-6 intake.

CONCLUSIONS

The findings are consistent with the known metabolic dependency of vitamin B-6 on riboflavin status and indicate that riboflavin may be the limiting nutrient, particularly in older people, for maintaining adequate vitamin B-6 status.

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.

Identifying Key Predictors of Cognitive Dysfunction in Older People Using Supervised Machine Learning Techniques: Observational Study

BACKGROUND

Machine learning techniques, specifically classification algorithms, may be effective to help understand key health, nutritional, and environmental factors associated with cognitive function in aging populations.

OBJECTIVE

This study aims to use classification techniques to identify the key patient predictors that are considered most important in the classification of poorer cognitive performance, which is an early risk factor for dementia.

METHODS

Data were used from the Trinity-Ulster and Department of Agriculture study, which included detailed information on sociodemographic, clinical, biochemical, nutritional, and lifestyle factors in 5186 older adults recruited from the Republic of Ireland and Northern Ireland, a proportion of whom (987/5186, 19.03%) were followed up 5-7 years later for reassessment. Cognitive function at both time points was assessed using a battery of tests, including the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS), with a score <70 classed as poorer cognitive performance. This study trained 3 classifiers-decision trees, Naïve Bayes, and random forests-to classify the RBANS score and to identify key health, nutritional, and environmental predictors of cognitive performance and cognitive decline over the follow-up period. It assessed their performance, taking note of the variables that were deemed important for the optimized classifiers for their computational diagnostics.

RESULTS

In the classification of a low RBANS score (<70), our models performed well (F₁ score range 0.73-0.93), all highlighting the individual's score from the Timed Up and Go (TUG) test, the age at which the participant stopped education, and whether or not the participant's family reported memory concerns to be of key importance. The classification models performed well in classifying a greater rate of decline in the RBANS score (F₁ score range 0.66-0.85), also indicating the TUG score to be of key importance, followed by blood indicators: plasma homocysteine, vitamin B6 biomarker (plasma pyridoxal-5-phosphate), and glycated hemoglobin.

CONCLUSIONS

The results suggest that it may be possible for a health care professional to make an initial evaluation, with a high level of confidence, of the potential for cognitive dysfunction using only a few short, noninvasive questions, thus providing a quick, efficient, and noninvasive way to help them decide whether or not a patient requires a full cognitive evaluation. This approach has the potential benefits of making time and cost savings for health service providers and avoiding stress created through unnecessary cognitive assessments in low-risk patients.

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.

Dietary Profiles, Nutritional Biochemistry Status, and Attention-Deficit/Hyperactivity Disorder: Path Analysis for a Case-Control Study

This study aims to investigate dietary and nutritional biochemistry profiles of attention-deficit/hyperactivity disorder (ADHD) and to explore their potential relationship by path analysis. We enrolled 216 children with ADHD and 216 age-, height- and gender-matched controls from 31 elementary schools in Taiwan. Dietary intake of the participants was assessed using a food frequency questionnaire (FFQ). Fasting blood samples were collected to determine the serum levels of multiple nutritional markers. Moreover, we employed a structural equation model (SEM) to link diet, nutritional markers and ADHD. Compared to healthy control, ADHD children had significantly lower serum levels of vitamin B12, folate, vitamin B6, ferritin concentration, and monounsaturated fatty acids (MUFA), but higher levels of serum saturated fatty acids (SFA), n-6/n-3 fatty acid ratio, and inorganic phosphorous concentration. Children with ADHD had more intake of nutrient-poor foods such as high sugar and high fat foods, and had less intake of vegetable, fruit, protein-rich foods than their counterpart. SEM analysis showed that the poor nutritional biochemistry profiles linked the association between unhealthy dietary patterns and ADHD. In conclusion, an unhealthy dietary pattern may be a predecessor of the poor nutritional biochemistry status, and managing diet and nutrition conditions should be considered to improve ADHD symptoms in children.

Simultaneous measurement of whole blood vitamin B1 and vitamin B6 using LC-ESI-MS/MS

Vitamin B1 and B6 have recently been included in the Dutch clinical guidelines for the general practitioner in the differential diagnosis of dementia. To keep up with the sharp rise in the number of requests, an LC-MS/MS method using stable isotopes as internal standards was developed. The active vitamers thiamine pyrophosphate (TPP) and pyridoxal-5'-phosphate (PLP) in whole blood are simultaneously measured with a short run time of 2min. Whole blood is mixed with internal standard solution containing both TPP-d3 and PLP-d3, followed by deproteinization with a trichloroacetic acid (TCA) solution. A UPLC-MS/MS system from Waters™ was used for chromatographic separation and subsequent detection by electrospray ionization in the positive mode with mass transitions of 425.1>121.85 for TPP and 247.9>149.9 for PLP. The method is linear across the range of 12-4870 nmol/L for TPP and 6-4850 nmol/L for PLP. The mean intra-assay and inter-assay precision are 3.5% and 7.6% respectively for TPP and 3.4% and 6.1% for PLP. The relative matrix effect (TPP 97%, PLP 93%), recovery (TPP 99%, PLP 94%) and lower limit of quantification (TPP 12 nmol/L, PLP 6 nmol/L) meet the applied acceptance criteria. The comparison of the new LC-ESI-MS/MS method for TPP with our current HPLC-Fluorescence method for total thiamine yields the following equation: TPP LC-MS/MS=0.97×total thiamine HPLC - 10.61 (r²=0.94). The comparison of the new LC-ESI-MS/MS method for PLP with our current LC-ESI-MS/MS method results in PLP LC-MS/MS new=1.01×PLP LC-MS/MS old - 1.58 (r²=0.99). In conclusion, this LC-MS/MS based assay is characterized by simple sample processing with a short run time and comparison with the current methods is excellent. The new LC-MS/MS method is a convenient method to determine TPP and PLP in whole blood for both clinical routine and research applications.

Vitamin B-6 deficiency is common and associated with poor long-term outcome in renal transplant recipients

Background: Previous studies have reported low circulating concentrations of pyridoxal-5-phospate (PLP) in renal transplant recipients (RTRs). It is unknown whether this is because of low intake or altered handling, and it is also unknown whether variation in circulating concentrations of PLP influences long-term outcome.Objective: We compared vitamin B-6 intake and circulating PLP concentrations of RTRs with those of healthy controls and investigated long-term clinical implications of vitamin B-6 deficiency in stable outpatient RTRs.Design: In a longitudinal cohort of 687 stable RTRs (57% male; mean ± SD age: 53 ± 13 y) with a median (IQR) follow-up of 5.3 y (4.8-6.1 y) and 357 healthy controls (47% male; age 54 ± 11 y), baseline vitamin B-6 was measured as plasma PLP by high-performance liquid chromatography (HPLC). Vitamin B-6 deficiency was defined as PLP <20 nmol/L, and insufficiency as PLP 20-30 nmol/L. Dietary intake was assessed by validated food-frequency questionnaires.Results: At inclusion [5.3 y (1.8-12.1 y) after transplantation], the mean vitamin B-6 intakes in RTRs and healthy controls were 1.77 ± 0.49 and 1.85 ± 0.56 mg/d, respectively (P = 0.23). In these groups, the median plasma PLP concentrations were 29 nmol/L (17-50 nmol/L) and 41 nmol/L (29-60 nmol/L), respectively (P < 0.001). Accordingly, deficiency was present in 30% of RTRs compared with 11% of healthy controls. PLP concentrations were inversely associated with glucose homeostasis variables and inflammation variables (all P < 0.01). During follow-up, 149 (21%) RTRs died and 82 (12%) developed graft failure. In RTRs, vitamin B-6 deficiency was associated with considerably higher mortality risk (HR 2.14; 95% CI: 1.48, 3.08) than a sufficient vitamin B-6 status, independent of potential confounders. No associations were observed for graft failure (P = 0.18).Conclusions: Vitamin B-6 deficiency is common in RTRs and does not seem to be a consequence of inadequate intake. In addition, this deficient state is clinically relevant and independently associated with an increased risk of mortality in RTRs. The cohort on which the study was based [TransplantLines Food and Nutrition Biobank and Cohort Study (TxL-FN)] was registered at clinicaltrials.gov as NCT02811835.

Inflammation, vitamin B6 and related pathways

The active form of vitamin B6, pyridoxal 5'-phosphate (PLP), serves as a co-factor in more than 150 enzymatic reactions. Plasma PLP has consistently been shown to be low in inflammatory conditions; there is a parallel reduction in liver PLP, but minor changes in erythrocyte and muscle PLP and in functional vitamin B6 biomarkers. Plasma PLP also predicts the risk of chronic diseases like cardiovascular disease and some cancers, and is inversely associated with numerous inflammatory markers in clinical and population-based studies. Vitamin B6 intake and supplementation improve some immune functions in vitamin B6-deficient humans and experimental animals. A possible mechanism involved is mobilization of vitamin B6 to the sites of inflammation where it may serve as a co-factor in pathways producing metabolites with immunomodulating effects. Relevant vitamin B6-dependent inflammatory pathways include vitamin B6 catabolism, the kynurenine pathway, sphingosine 1-phosphate metabolism, the transsulfuration pathway, and serine and glycine metabolism.

Digestion and Postprandial Metabolism in the Elderly

The elderly are an increasing segment of the population. Despite the rapid gains in medical knowledge and treatments, older adults are more likely to experience chronic illnesses that decrease quality of life and accelerate mortality. Nutrition is a key modifiable lifestyle factor which greatly impacts chronic disease risk. Yet despite the importance of nutrition, relatively little is known of the impact of advancing age on the gastrointestinal function, the digestive responses, and the post-meal metabolic adaptations that occur in response to ingested food. Knowledge of the age-related differences in digestion and metabolism in the elderly is essential to the development of appropriate nutritional recommendations for the maintenance of optimal health and prevention of disease.

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 in plasma and cerebrospinal fluid of children

Background

Over the past years, the essential role of vitamin B6 in brain development and functioning has been recognized and genetic metabolic disorders resulting in functional vitamin B6 deficiency have been identified. However, data on B6 vitamers in children are scarce.

Materials and Methods

B6 vitamer concentrations in simultaneously sampled plasma and cerebrospinal fluid (CSF) of 70 children with intellectual disability were determined by ultra performance liquid chromatography-tandem mass spectrometry. For ethical reasons, CSF samples could not be obtained from healthy children. The influence of sex, age, epilepsy and treatment with anti-epileptic drugs, were investigated.

Results

The B6 vitamer composition of plasma (pyridoxal phosphate (PLP) > pyridoxic acid > pyridoxal (PL)) differed from that of CSF (PL > PLP > pyridoxic acid > pyridoxamine). Strong correlations were found for B6 vitamers in and between plasma and CSF. Treatment with anti-epileptic drugs resulted in decreased concentrations of PL and PLP in CSF.

Conclusion

We provide concentrations of all B6 vitamers in plasma and CSF of children with intellectual disability (±epilepsy), which can be used in the investigation of known and novel disorders associated with vitamin B6 metabolism as well as in monitoring of the biochemical effects of treatment with vitamin B6.

Vitamin B-6 vitamers in human plasma and cerebrospinal fluid

BACKGROUND

Vitamin B-6 comprises a group of 6 interrelated vitamers and is essential for numerous physiologic processes, including brain functioning. Genetic disorders disrupting vitamin B-6 metabolism have severe clinical consequences.

OBJECTIVE

To adequately diagnose known and novel disorders in vitamin B-6 metabolism, a reference set is required containing information on all vitamin B-6 vitamers in plasma and cerebrospinal fluid (CSF).

DESIGN

Concentrations of vitamin B-6 vitamers in the plasma and CSF of 533 adult subjects were measured by ultra high-performance liquid chromatography-tandem mass spectrometry.

RESULTS

The relative vitamin B-6 vitamer composition of plasma [pyridoxal phosphate (PLP) > pyridoxic acid (PA) > pyridoxal] differed from that of CSF (pyridoxal > PLP > PA > pyridoxamine). Sex influenced vitamin B-6 vitamer concentrations in plasma and CSF and should therefore be taken into account when interpreting vitamin B-6 vitamer concentrations. The strict ratios and strong correlations between vitamin B-6 vitamers point to a tight regulation of vitamin B-6 vitamer concentrations in blood and CSF. Given the unique design of this study, with simultaneously withdrawn blood and CSF from a large number of subjects, reliable CSF:plasma ratios and correlations of vitamin B-6 vitamers could be established.

CONCLUSIONS

We provide an extensive reference set of vitamin B-6 vitamer concentrations in plasma and CSF. In addition to providing insight on the regulation of individual vitamers and their intercompartmental distribution, we anticipate that these data will prove to be a valuable reference set for the diagnosis and treatment of conditions associated with altered vitamin B-6 metabolism.

Vitamin B6 in plasma - sample stability and the reference limits

Quantitatively, the most important B6 vitamer in plasma is pyridoxal-5'-phosphate (p-PLP). The prerequisite for the use of p-PLP measurements in patients with poor nutritional status is an appropriate reference interval, together with knowledge of the stability of vitamin B6 in plasma samples. We used blood samples from healthy blood donors to derive the reference limits for p-PLP, and to examine its stability for 24 hours at room temperature and at 4-8°C. P-PLP was measured using high performance liquid chromatography (HPLC). The reference interval in adults was 23-223 nmol/L. P-PLP was stable for 24 h at room temperature and at 4-8°C, allowing time for normal specimen transport.

Low plasma vitamin B-6 status affects metabolism through the kynurenine pathway in cardiovascular patients with systemic inflammation

It is unclear whether reduced plasma pyridoxal 5'-phosphate (PLP) during inflammation reflects an altered distribution or increased requirement of vitamin B-6 that may impair overall vitamin B-6 status in tissues. In plasma from 3035 patients undergoing coronary angiography for suspected coronary heart disease, we investigated if plasma concentrations of any metabolites in the kynurenine pathway, which depend on PLP as cofactor, may serve as metabolic marker(s) of vitamin B-6 status. We also examined the association of vitamin B-6 status with serum or plasma concentrations of several inflammatory markers. Among the kynurenines, only 3-hydroxykynurenine (HK) was inversely related to PLP and showed a positive relation to 4 investigated inflammatory markers. A segmented relationship was observed between PLP and HK, with a steep slope at PLP concentrations < 18.4 nmol/L, corresponding to the 5th percentile, and an almost zero slope at higher PLP concentrations. Low PLP and the steep PLP-HK slope were essentially confined to participants with 1 or more inflammatory markers in the upper tertile. Oral supplementation with pyridoxine hydrochloride (40 mg/d) for 1 mo increased plasma PLP 8-fold, reduced the geometric mean (95% CI) of HK from 29.5 to 20.2 nmol/L (P < 0.001), and abolished the steep segment of the PLP-HK curve. The steep inverse relationship of plasma PLP with HK at low plasma PLP and the lowering of HK by pyridoxine suggest plasma HK as a metabolic marker of vitamin B-6 status. Thus, low plasma PLP during inflammation may reflect impaired cellular vitamin B-6 status, as indicated by the concurrent increase in plasma HK.

Vitamin B6: Beyond Adequacy

There is good agreement concerning average requirements and reference intakes for vitamin B6 but less agreement over safe upper levels from supplements. High-dose supplements cause sensory nerve damage. Supplements of vitamin B6 have been advocated for treatment of the premenstrual syndrome, with little evidence of efficacy. There are plausible mechanisms for an antidepressant action and protection against steroid hormone—dependent cancers but no evidence from clinical trials. Pyridoxamine reduces the glycation of proteins and so could be beneficial in preventing the adverse effects of poor glycemic control in diabetes. There are plausible mechanisms for an antihypertensive action but only suggestive evidence from small intervention trials. There is no evidence that supplements of vitamin B6 have any beneficial effect in hyperhomocysteinemia. There is neither a plausible mechanism nor any evidence from controlled trials for any effect of supplements of vitamin B6 in preventing a decline in cognitive function with aging, amelioration of dementia or autism, or improvement of the carpal tunnel syndrome.

Biochemical risk indices, including plasma homocysteine, that prospectively predict mortality in older British people: the National Diet and Nutrition Survey of People Aged 65 Years and Over

Predictive power, for total and vascular mortality, of selected indices measured at baseline in the British National Diet and Nutrition Survey (community-living subset) of People Aged 65 Years and Over was tested. Mortality status and its primary and underlying causes were recorded for 1100 (mean age 76.7 (sd 7.5) years, 50.2% females) respondents from the baseline survey in 1994-5 until September 2008. Follow-up data analyses focussed especially on known predictors of vascular disease risk, together with intakes and status indices of selected nutrients known to affect, or to be affected by, these predictors. Total mortality was significantly predicted by hazard ratios of baseline plasma concentrations (per sd) of total homocysteine (tHcy) (95% CI) 1.19 (1.11, 1.27), pyridoxal phosphate 0.90 (0.81, 1.00), pyridoxic acid 1.10 (1.03, 1.19), alpha1-antichymotrypsin 1.21 (1.13, 1.29), fibrinogen 1.14 (1.05, 1.23), creatinine 1.20 (1.10, 1.31) and glycosylated Hb 1.23 (1.14, 1.32), and by dietary intakes of energy 0.87 (0.80, 0.96) and protein 0.86 (0.77, 0.97). Prediction patterns and significance were similar for primary-cause vascular mortality. The traditional risk predictors plasma total and HDL cholesterol were not significant mortality predictors in this age group, nor were the known tHcy-regulating nutrients, folate and vitamin B12 (intakes and status indices). Model adjustment for known risk predictors resulted in the loss of significance for some of the afore-mentioned indices; however, tHcy 1.34 (1.04, 1.73) remained a significant predictor for vascular mortality. Thus, total and primary vascular mortality is predicted by energy and protein intakes, and by biochemical indices including tHcy, independent of serum folate or vitamin B12.

Vitamins B2 and B6 and genetic polymorphisms related to one-carbon metabolism as risk factors for gastric adenocarcinoma in the European prospective investigation into cancer and nutrition

B vitamins and polymorphisms in genes coding for enzymes involved in one-carbon metabolism may affect DNA synthesis and methylation and thereby be implicated in carcinogenesis. Previous data on vitamins B2 and B6 and genetic polymorphisms other than those involving MTHFR as risk factors for gastric cancer (GC) are sparse and inconsistent. In this case-control study nested within the European Prospective Investigation into Cancer and Nutrition cohort, cases (n = 235) and controls (n = 601) were matched for study center, age, sex, and time of blood sampling. B2 and B6 species were measured in plasma, and the sum of riboflavin and flavin mononucleotide was used as the main exposure variable for vitamin B2 status, whereas the sum of pyridoxal 5'-phosphate, pyridoxal, and 4-pyridoxic acid was used to define vitamin B6 status. In addition, we determined eight polymorphisms related to one-carbon metabolism. Relative risks for GC risk were calculated with conditional logistic regression, adjusted for Helicobacter pylori infection status and smoking status. Adjusted relative risks per quartile (95% confidence interval, P(trend)) were 0.85 (0.72-1.01, 0.06) for vitamin B2 and 0.78 (0.65-0.93, <0.01) for vitamin B6. Both relations were stronger in individuals with severe chronic atrophic gastritis. The polymorphisms were not associated with GC risk and did not modify the observed vitamin-cancer associations. In summary, results from this large European cohort study showed an inverse association between vitamin B2 and GC risk, which is borderline significant, and a significant inverse association between vitamin B6 and GC risk.

Plasma vitamin B(6) and risk of myocardial infarction in women

BACKGROUND

We prospectively evaluated the relationships between fasting plasma levels of vitamin B(6), as pyridoxal phosphate, and subsequent myocardial infarction risk in women.

METHODS AND RESULTS

Among 32 826 women who provided blood samples between 1989 and 1990 (27% of the original 1976 cohort), 239 were diagnosed with incident myocardial infarction (fatal and nonfatal) after blood collection but before July 1998. Of these women, 144 had provided a sample after fasting >10 hours. Cases were matched 1:2 by age, cigarette smoking status, and month of and fasting status at the time of blood collection with controls from the same cohort. Conditional logistic regression was used to adjust for potential confounders, including traditional coronary risk factors, anthropometric factors, dietary intake, and selected biomarkers. Median age at blood collection was 63 years. Plasma levels of pyridoxal phosphate were inversely associated with risk of myocardial infarction; the multivariable-adjusted rate ratio for the highest compared with the lowest quartiles (>70 versus <27.9 pmol/mL) was 0.22 (95% confidence interval, 0.09 to 0.55; P for trend=0.05). The association varied by age: among women who were <60 years of age at blood sampling, the rate ratio comparing the highest and lowest quartiles was 0.05 (95% confidence interval, 0.004 to 0.61), whereas among older women, the corresponding rate ratio was 0.36 (95% confidence interval, 0.13 to 1.02).

CONCLUSIONS

Fasting plasma concentration of pyridoxal phosphate was inversely associated with myocardial infarction risk, an effect that was in part independent of dietary B(6) intake. In addition to dietary vitamin B(6) intake, there are other determinants of plasma vitamin B(6) status, and these factors warrant further research.

Quantitative profiling of biomarkers related to B-vitamin status, tryptophan metabolism and inflammation in human plasma by liquid chromatography/tandem mass spectrometry

Vitamins B2 and B6 serve as cofactors in enzymatic reactions involved in tryptophan and homocysteine metabolism. Plasma concentrations of these vitamins and amino acids are related to smoking and inflammation, and correlate with other markers of immune activation. Large-scale studies of these relations have been hampered by lack of suitable analytical methods. The assay described includes riboflavin, five vitamin B6 forms (pyridoxal 5'-phosphate, pyridoxal, 4-pyridoxic acid, pyridoxine and pyridoxamine), tryptophan and six tryptophan metabolites (kynurenine, kynurenic acid, anthranilic acid, 3-hydroxykynurenine, xanthurenic acid and 3-hydroxyanthranilic acid), cystathionine, neopterin and cotinine. Trichloroacetic acid containing 13 isotope-labelled internal standards was added to 60 microL of plasma, the mixture was centrifuged, and the resulting supernatant used for analysis. The analytes were separated within 5 min on a stable-bond C8 column by a gradient-type mobile phase containing acetonitrile, heptafluorobutyric acid and high concentration (650 mmol/L) of acetic acid, and detected using electrospray ionization tandem mass spectrometry (ESI-MS/MS). The mobile phase ensured sufficient separation and high ionization efficiency of all analytes. Recoveries were 75-123% and within-day and between-day coefficients of variance (CVs) were 2.5-9.5% and 5.4-16.9%, respectively. Limits of detection ranged from 0.05 to 7 nmol/L. The method enables quantification of endogenous plasma concentrations of 16 analytes related to B-vitamin status and inflammation, and may prove useful in large-scale epidemiological studies.

Plasma pyridoxal 5'-phosphate in the US population: the National Health and Nutrition Examination Survey, 2003-2004

BACKGROUND

No large-scale, population-based study has considered the descriptive epidemiology of vitamin B-6 status with use of plasma pyridoxal 5'-phosphate (PLP), the indicator of vitamin B-6 adequacy used to set the current Recommended Dietary Allowance, which is < or = 2 mg/d for all subgroups.

OBJECTIVES

We sought to examine the epidemiology of vitamin B-6 status in the US population.

METHODS

In > 6000 participants aged > or = 1 y in the National Health and Nutrition Examination Survey (2003-2004), we considered relations between plasma PLP and various subject characteristics and examined trends in plasma PLP and homocysteine with vitamin B-6 intake, both overall and in selected subgroups.

RESULTS

In males, plasma PLP decreased with age after adolescence only in nonusers of supplemental vitamin B-6. Regardless of supplement use, plasma PLP concentrations of women of childbearing age were significantly lower than those of comparably aged men, and most oral contraceptive users had plasma PLP < 20 nmol/L. The prevalence of low plasma PLP was significantly > 3% at vitamin B-6 intakes from 2 to 2.9 mg/d in all subgroups and at intakes from 3 to 4.9 mg/d in smokers, the elderly, non-Hispanic blacks, and current and former oral contraceptive users. Intakes from 3 to 4.9 mg/d compared with < 2 mg/d were associated with significant protection from low plasma PLP in most subgroups and from hyperhomocysteinemia in the elderly.

CONCLUSIONS

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.

Plasma vitamin B-6 forms and their relation to transsulfuration metabolites in a large, population-based study

BACKGROUND

Vitamin B-6 exists in different forms; one of those forms, pyridoxal 5'-phosphate (PLP), serves a cofactor in many enzyme reactions, including the transsulfuration pathway, in which homocysteine is converted to cystathionine and then to cysteine. Data on the relations between indexes of vitamin B-6 status and transsulfuration metabolites in plasma are sparse and conflicting.

OBJECTIVE

We investigated the distribution and associations of various vitamin B-6 species in plasma and their relation to plasma concentrations of transsulfuration metabolites.

DESIGN

Nonfasting blood samples from 10 601 healthy subjects with a mean age of 56.4 y were analyzed for all known vitamin B-6 vitamers, folate, cobalamin, riboflavin, total homocysteine, cystathionine, total cysteine, methionine, and creatinine. All subjects were genotyped for the methylenetetrahydrofolate reductase (MTHFR) 677C-->T polymorphism.

RESULTS

Plasma concentrations of the main vitamin B-6 vitamers--PLP, pyridoxal, and 4-pyridoxic acid--were strongly correlated. Among the vitamin B-6 vitamers, PLP showed the strongest and most consistent inverse relation to total homocysteine and cystathionine, but the dose response was different for the 2 metabolites. The PLP-total homocysteine relation was significant only in the lowest quartile of the vitamin B-6 distribution and was strongest in subjects with the MTHFR 677TT genotype, whereas cystathionine showed a graded response throughout the range of vitamin B-6 vitamer concentrations, and the effect was not modified by the MTHFR 677C-->T genotype.

CONCLUSION

This large population-based study provided precise estimates of the relation between plasma concentrations of vitamin B-6 forms and transsulfuration metabolites as modified by the MTHFR 677C-->T genotype.

Maternal plasma pyridoxal-5'-phosphate concentrations and risk of isolated oral clefts in the Philippines

BACKGROUND

We report that inadequate vitamin B-6 status of Filipino mothers, assessed by erythrocyte aspartate aminotransferase activity coefficient (EAST-AC), is associated with an increased risk for isolated cleft lip with or without cleft palate (CL/P) in their children. Its association with the status assessed by plasma pyridoxal-5'-phosphate (PLP) concentrations is unknown.

METHODS

In a case-control study in the Philippines including 46 cases (mothers of a child with CL/P) and 392 controls (mothers of an unaffected child), we evaluated the association between the risk for CL/P and maternal vitamin B-6 status assessed by PLP and EAST-AC.

RESULTS

The ORs of CL/P were estimated by classifying mothers by PLP (>30, 20-30, and <20 nmol/L). Using the highest PLP group as the reference, ORs (95% CIs) were 1.03 (0.45-2.37) and 2.66 (1.30-5.50) for the middle and lowest groups, respectively (p trend = .01). In multivariate models controlling for various covariates including folate, the risk for CL/P was approximately 12 times higher in mothers with inadequate vitamin B-6 status, assessed by both PLP and EAST-AC values, compared to those with adequate status by both values.

CONCLUSIONS

Inadequate vitamin B-6 status assessed by maternal PLP and EAST-AC values independently and both combined was associated with an increased risk for CL/P. The association was highest when both values were considered, suggesting that the measurement of both PLP and EAST-AC provides better assessment of vitamin B-6 status than either measurement alone.

Serum homocysteine is related to food intake in adolescents: the Child and Adolescent Trial for Cardiovascular Health

BACKGROUND

An understanding of the relation in adolescents between serum homocysteine and foods rich in vitamin B-6, vitamin B-12, and folate is important because high homocysteine concentrations in childhood and adolescence may be a risk factor for later cardiovascular disease. However, little is known about the relation between food intake and homocysteine in adolescents.

OBJECTIVE

Five years after national folic acid fortification of enriched grain products, cross-sectional relations between food intake and serum homocysteine concentrations were examined in 2695 adolescents [x age: 18.3 (range: 15-20) y] enrolled in the Child and Adolescent Trial for Cardiovascular Health.

DESIGN

A nonfasting blood specimen was analyzed for serum homocysteine, folate, and vitamins B-6 and B-12. Dietary intake was assessed by using a food-frequency questionnaire. Multiple regression analyses were used to evaluate the relation of intakes of whole grains, refined grains, fruit, vegetables, dairy products, red and processed meats, and poultry with serum homocysteine concentrations after adjustment for demographic characteristics, lifestyle factors, and food intake.

RESULTS

Serum homocysteine concentrations were lower with greater intakes of whole grains (P for trend = 0.002), refined grains (P for trend = 0.02), and dairy foods (P for trend <0.001); were higher with greater intake of poultry (P for trend = 0.004); and were not related to intakes of fruit, vegetables, or red or processed meat. After additional adjustment for serum B vitamins, the relations of serum homocysteine with most food groups were attenuated.

CONCLUSION

These observational findings suggest a beneficial effect of whole-grain, refined-grain, and dairy products on serum homocysteine concentrations in an adolescent population.

Multianalyte quantification of vitamin B6 and B2 species in the nanomolar range in human plasma by liquid chromatography-tandem mass spectrometry

BACKGROUND

Homocysteine, a risk factor of cardiovascular disease, cognitive disorders, and pregnancy complications, exists at a point of metabolic convergence of several B vitamins, including vitamins B(6) and B(2) (riboflavin). Measurement of the various forms of these vitamins may be useful for the study of hyperhomocysteinemia as well as for the assessment of vitamin status.

METHODS

Plasma (60 microL) was deproteinized by mixing with an equal volume of 50 g/L trichloroacetic acid that contained d(2)-pyridoxal 5'-phosphate, d(3)-pyridoxal, and d(8)-riboflavin as internal standards. Pyridoxal (PL), pyridoxal 5'-phosphate (PLP), pyridoxine (PN), pyridoxine 5'-phosphate, pyridoxamine (PM), pyridoxamine 5'-phosphate, 4-pyridoxic acid (PA), riboflavin, flavin mononucleotide (FMN), and FAD were separated on a C(8) reversed-phase column, which was developed with an acetonitrile gradient in a buffer containing acetic acid and heptafluorobutyric acid. The analytes were detected by tandem mass spectrometry in the positive-ion mode.

RESULTS

The chromatographic run lasted 8 min. Within- and between-day CVs were 3%-20% and 6%-22%, respectively, and recoveries were 78%-163%. Limits of detection (signal-to-noise ratio = 5) were in the range 0.1-4.0 nmol/L, and the response was linear over several orders of magnitude. In samples from 94 healthy persons, we obtained median concentrations (nmol/L) of 35.4 for PLP, 16.9 for PL, 22.4 for PA, 10.3 for riboflavin, 7.5 for FMN, and 63.1 for FAD. PN and PM were also detected in some cardiovascular patients taking B(6) supplements.

CONCLUSIONS

This method based on liquid chromatography-tandem mass spectrometry measures all known plasma forms of vitamins B(6) and B(2), which span a wide range of polarity. The assay is characterized by simple sample processing with no derivatization, low sample volume requirement, and a short run time.

Correlates of plasma homocysteine, cysteine and cysteinyl-glycine in respondents in the British National Diet and Nutrition Survey of young people aged 4-18 years, and a comparison with the survey of people aged 65 years and over

Plasma total homocysteine (tHcy), cysteine and cysteinyl-glycine were measured in a representative sample of 922 young people aged 4-18 years, participating in the National Diet and Nutrition Survey in mainland Britain in 1997. Both tHcy and cysteine increased markedly with age; cysteinyl-glycine less so. Neither tHcy nor cysteine differed between genders; cysteinyl-glycine was higher in males. tHcy concentrations were lowest in the winter; cysteine and cysteinyl-glycine varied only slightly with season. In respondents aged >15 years, tHcy was higher in smokers, but in respondents aged 7-11 years, tHcy was higher in those whose mothers smoked. tHcy was inversely correlated with serum folate, serum vitamin B12 and vitamin B6 status, but neither cysteine nor cysteinyl-glycine shared these relationships. The relationships between tHcy and B-vitamin status indices ran parallel with those of the 65 years and over survey, but at much lower tHcy concentrations for any given B-vitamin concentration. Age-adjusted tHcy was not correlated with anthropometric indices, blood pressure, haematology, plasma creatinine, urea or cholesterol, but was directly correlated with fasting triacylglycerol. We conclude that disease-risk indices, like tHcy and perhaps cysteine, if established during early life, may be modulated by diet and lifestyle, thereby providing an opportunity for public health intervention.