Labelling with stable isotopes is a powerful technique when used in metabolic studies. However, there is some doubt that absorption from a test meal labelled 'extrinsically' with a stable isotope compound will behave in the same manner as the same naturally occurring 'intrinsically' labelled compound. Three growing methods were investigated, and a method for growing spinach containing intrinsically labelled 5-methyltetrahydrofolic acid (5-CH3-H-4-PteGlu) using as nutrient-flow hydroponic system and a nutrient solution containing 50% of the nitrate as N-15 nitrate is described. The resulting plants contained 630 mu g kg(-1) 5-CH3-H-4-PteGlu with 40% of the nitrogen present as N-15. After feeding, appearance of 5-CH3-H-4-PteGlu in the plasma derived from the test meal could be identified by liquid chromatography/mass spectrometry. (c) 2006 Elsevier Ltd. All rights reserved.

Single (13)C(6)-labeled doses of pteroylmonoglutamic acid (PteGlu: 634 nmol; n = 14), (6S-)5-formyltetrahydrofolic acid (431-569 nmol; n = 16), or [(15)N(1-7)]-intrinsically labeled spinach (mainly 5-methyltetrahydrofolate) (588 nmol; n = 14) were fed to fasting adult volunteers. Plasma-labeled 5-methyltetrahydrofolic acid responses were monitored for 8 h. There was a slower rate of increase in plasma-labeled 5-methyltetrahydrofolic acid and longer time to peak (171 +/- 9 min; mean +/- SEM) following an oral dose of [(13)C(6)]PteGlu than either [(13)C(6)]5-formyltetrahydrofolic acid (54 +/- 10 min) or [(15)N(1-7)]spinach folate (60 +/- 13 min) suggesting saturated metabolic capacity for the biotransformation of PteGlu. Mathematical modeling generated a significantly higher mean "apparent absorption" for 5-formyltetrahydrofolic acid (38%) and spinach folate (44%) than for PteGlu (24%). The high "relative absorption" of reduced folates to PteGlu was unexpected given that PteGlu itself, from (14)C-tracer mass balance experiments, is almost completely absorbed. Although it is ubiquitously accepted that a physiological dose of PteGlu is reduced and methylated in the epithelial cells of the small intestine, and that essentially only 5-methyltetrahydrofolic acid is exported into the hepatic portal vein (HPV), as is the case for absorbed reduced 1-carbon-substituted folates, modeling indicated greater liver sequestration when PteGlu was used as the test dose, suggesting that PteGlu enters the HPV unaltered and that the liver is the primary site of initial metabolism. Because of the observed differential plasma response and the hypothesized difference in the site of initial metabolism, the historical use of PteGlu as a "reference folate" in studies of folate bioavailability is seriously questioned.

Reports on the effects of carotenoids are conflicting. The present paper examines similarities and differences from contiguous studies in vitro and in vivo. Single-cell gel electrophoresis was used to measure the frequency of single-strand breaks (SSB) in the cell line MOLT-17 (as a model system) and human peripheral blood lymphocytes (PBL). MOLT-17 cells were supplemented with β-carotene, lutein or lycopene at a range of concentrations (0·00–8·00 μmol/l) using a liposome delivery method. Uptake was dose-dependent. β-Carotene concentration in the media had no effect on SSB in control cells, but incubation with lycopene or lutein (>2·00 μmol/l) increased the numbers of SSB in control cells. MOLT-17 DNA was less susceptible to oxidative damage (100 μmol H2O2/l, 5 min, 4 °C) following incubation with carotenoids between 0·50 and 1·00 μmol/l; at >1·00 μmol/l the effects were ambiguous. Apparently healthy male volunteers supplemented their habitual diets with lutein, β-carotene or lycopene (natural isolate capsules, 15 mg/d, 4 weeks) in three independent studies, raising plasma concentrations to different extents. Lycopene and lutein had no effect on SSB in control PBL or following oxidative challenge. However, increased plasma β-carotene was associated with more SSB in control cells whilst PBL DNA resistance to oxidative damage ex vivo was unaffected. These results suggest that the carotenoids are capable of exerting two overlapping but distinct effects: antioxidant protection by scavenging DNA-damaging free radicals and modulation of DNA repair mechanisms.

Single (13)C6-labelled doses of pteroylmonoglutamic acid (PteGlu; 634 nmol) or 5-formyltetrahydrofolic acid (431-569 nmol) were given to fasted adult volunteers, and the rise in total and (13)C-labelled plasma 5-methyltetrahydrofolic acid metabolite monitored over 8 h by HPLC and liquid chromatography-MS. The dose-adjusted area under the curve (AUC) for total (labelled plus unlabelled) plasma 5-methyltetrahydrofolic acid following a 5-formyltetrahydrofolic acid test dose was 155 % that obtained following a PteGlu test dose. Surprisingly, an average 60 and 40 % of the total plasma 5-methyltetrahydrofolic acid response to [(13)C6]PteGlu and [(13)C6]5-formyltetrahydrofolic acid, respectively, was unlabelled; an observation never before reported. Short-term kinetics of plasma [(13)C6]5-methyltetrahydrofolic acid showed a slower initial rate of increase in plasma concentration and longer time to peak following an oral dose of [(13)C6]PteGlu compared with that for an oral dose of [(13)C6]5-formyltetrahydrofolic acid, while the [(13)C6]5-methyltetrahydrofolic acid AUC for [(13)C6]5-formyltetrahydrofolic acid was 221 % that for [(13)C6]PteGlu. These data indicate that PteGlu and 5-formyltetrahydrofolic acid, which are thought to be well absorbed (about 90 %) at physiological doses, exhibit dramatically different rates and patterns of plasma response. A limitation in the rate of reduction of PteGlu before methylation could result in slower mucosal transfer of [(13)C6]5-methyltetrahydrofolic acid derived from [(13)C6]PteGlu into the plasma. This, when coupled with an observed similar plasma clearance rate for [(13)C6]5-methyltetrahydrofolic acid metabolite derived from either folate test dose, would yield a comparatively smaller AUC. These findings suggest potential problems in interpretation of absorption studies using unlabelled or labelled folates where the rate of increase, the maximum increase, or the AUC, of plasma folate is employed for test foods (mainly reduced folates) v. a 'reference dose' of PteGlu.

The purpose of the present paper is to review our current understanding of the chemistry and biochemistry of folic acid and related folates, and to discuss their impact on public health beyond that already established in relation to neural-tube defects. Our understanding of the fascinating world of folates and C1 metabolism, and their role in health and disease, has come a long way since the discovery of the B-vitamin folic acid by Wills (1931), and its first isolation by Mitchell et al. (1941). However, there is still much to do in perfecting methods for the measurement of folate bioavailability, and status, with a high extent of precision and accuracy. Currently, examination of the relationships between common gene polymorphisms involved in C1 metabolism and folate bioavailability and folate status, morbidity, mortality and longevity is evaluated as a series of individual associations. However, in the future, examination of the concurrent effects of such common gene polymorphisms may be more beneficial.

Within Europe there are differences in cardiovascular disease (CVD) risk between countries and this might be related to dietary habits. Oxidative modification of LDL is suggested to increase the risk of CVD and both the fatty acid and antioxidant content of LDL can affect its oxidation. In the present study, concentration of LDL fatty acid and antioxidant micronutrients (tocopherols and carotenoids) and ex vivo oxidative resistance of LDL (lag phase) was compared in volunteers from five countries with different fruit and vegetable intakes and reported rates of CVD. Eighty volunteers (forty males, forty females per centre), age range 25–45 years, were recruited from France, Northern Ireland, UK, Republic of Ireland, The Netherlands, and Spain, and their LDL composition and lag phase were measured. There were some differences in LDL carotenoid and α-tocopherol concentrations between countries. α-Tocopherol was low and β- + γ-tocopherol were high ( P <0·001) in the Dutch subjects. β-Carotene concentrations were significantly different between the French and Spanish volunteers, with French showing the highest and Spanish the lowest concentration. LDL lycopene was not different between centres in contrast to lutein, which was highest in French (twofold that in the Dutch and Spanish and threefold that in Northern Ireland and the Republic of Ireland, P <0·001). However absolute LDL saturated, monounsaturated, polyunsaturated and total unsaturated fatty acid concentrations were different between countries ( P <0·001, total unsaturated highest in Northern Ireland) there was little difference in unsaturated:saturated fatty acid concentration ratios and no difference in polyunsaturated:saturated fatty acid concentration ratios. LDL from the Republic of Ireland (a region with a high rate of CVD) had greater resistance to Cu-stimulated oxidation than samples obtained from volunteers in other countries. In conclusion, LDL composition did not predict resistance to Cu-stimulated oxidation, nor is there evidence that LDL from volunteers in countries with lower rates of CVD have greater resistance to oxidation.

Folic acid fortification, mandatory in the United States, is currently being considered by the UK. The hypothesis that the matrix of some cereal-product vehicles may result in low fortificant bioavailability was tested using a dual oral/intravenous (i.v.) isotopic-label approach, which was evaluated concurrently. Fifteen women received 225 microg oral folate (capsules, fortified white bread and fortified branflakes), mainly as folic acid labeled with (13)C on 6 carbons of the benzoyl ring ((13)C(6)-PteGlu), followed by i.v. injection of 100 microg folic acid labeled with (2)H on 4 hydrogens of the glutamic acid group ((2)H(4)-PteGlu). The urinary excretion ratio (UER) in intact folate of the percentage of labeled oral dose excreted divided by the percentage of i.v. dose excreted was used as the primary index of absorption. The geometric mean (95% confidence interval) UER for folic acid capsules was 3.68 (1.90, 7.14) at 24 h and 2.18 (1.24, 3.83) at 48 h. Because these were significantly in excess of 1.0, indicative of 100% absorption of the oral dose, it was concluded that oral and i.v. labeled folic acid are handled differently by the body and that "absolute" absorption cannot be calculated. Compared with the 48-h UER for folic acid capsules, the "relative" 48-h UER for white bread and branflakes was 0.71 and 0.37, respectively, indicating that some cereal-based vehicles may inhibit absorption of fortificant. However, even the validity of this "relative" approach is questioned.

The association of folates with the prevention of neural tube defects and reduced risk of other chronic diseases has stimulated interest in the development of techniques for the study of their bioavailability in humans. Stable isotope protocols differentiate between oral and/or intravenous test doses of folate and natural levels of folate already present in the body. An liquid chromatography/mass spectrometry (LC/MS) procedure is described that has been validated for the determination of [13C]5-methyltetrahydropteroyl monoglutamic acid ([13C]5-CH3H4PteGlu) in plasma and urine, following oral dosing of volunteers with different labeled folates. Folate binding protein affinity columns were used for sample purification prior to LC/MS determination. Chromatographic separation was achieved using a Superspher 100RP18 (4 microm) column and mobile phase of 0.1 mol/L acetic acid (pH 3.3):acetonitrile (90:10; 250 microL/min). Selected ion monitoring was conducted on the [M-H](-) ion: m/z 458 and 459 for analyzing 5-CH3H4PteGlu; m/z 464 [M+6-H](-) to determine 5-CH3H4PteGlu derived from the label dose; m/z 444 for analysis of 2H4PteGlu internal standard, and m/z 446 and 478 to confirm that there was no direct absorption of unmetabolized compounds. Calibration was linear over the range 0-9 x 10(-9) mol/L; the limits of detection and quantification were 0.2 x 10(-9) and 0.55 x 10(-9) mol/L, respectively. The mean coefficient of variation of the ratios (m/z 463/458) was 7.4%. The method has potential applications for other key folates involved in one-carbon metabolism.

Increased levels of oxidative stress have been implicated in tissue damage and the development of chronic diseases, and dietary antioxidants may reduce the risk of oxidative tissue damage. As part of a European multicentre project, several studies were undertaken with the aim of testing whether the consumption of foods rich in carotenoids reduces oxidative damage to human tissue components. We describe here the serum response of carotenoids and tocopherols upon supplementation with carotenoids from natural extracts (alpha-carotene+beta-carotene, lutein or lycopene; 15 mg/day) and/or with alpha-tocopherol (100 mg/day) in a multicentre, placebo-controlled intervention study in 400 healthy male and female volunteers, aged 25-45 years, from five European regions (France, Northern Ireland, Republic of Ireland, The Netherlands and Spain). Supplementation with alpha-tocopherol increased serum alpha-tocopherol levels, while producing a marked decrease in serum gamma-tocopherol. Supplementation with alpha- + beta-carotene (carotene-rich palm oil) resulted in 14-fold and 5-fold increases respectively in serum levels of these carotenoids. Supplementation with lutein (from marigold extracts) elevated serum lutein (approx. 5-fold), zeaxanthin (approx. doubled) and ketocarotenoids (although these were not present in the supplement), whereas lycopene supplementation (from tomato paste) resulted in a 2-fold increase in serum lycopene. The isomer distributions of beta-carotene and lycopene in serum remained constant regardless of the isomer composition in the capsules. In Spanish volunteers, additional data showed that the serum response to carotenoid supplementation reached a plateau after 4 weeks, and no significant side effects (except carotenodermia) or changes in biochemical or haematological indices were observed throughout the study. This part of the study describes dose-time responses, isomer distribution, subject variability and side effects during supplementation with the major dietary carotenoids in healthy subjects.

This article discusses the recent consultation by the UK Department of Health and Food Standards Agency on the risk-benefit of a whole population strategy for increased intake of folic acid via the fortification of flour. The potential benefit of folic acid in relation to decreased incidence of Neural Tube Defects in the newly born is contrasted to the potential risk of increasing permanent neuropathy (nerve damage) in those suffering from vitamin B12 deficiency. Questions are also raised with regard to the potential risk of folic acid addition in the context of pre-existing malignant neoplasms, and the incidence of dichorionic twin births.

High intakes of fruits and vegetables, or high circulating levels of their biomarkers (carotenoids, vitamins C and E), have been associated with a relatively low incidence of cardiovascular disease, cataract and cancer. Exposure to a high fruit and vegetable diet increases antioxidant concentrations in blood and body tissues, and potentially protects against oxidative damage to cells and tissues. This paper describes blood concentrations of carotenoids, tocopherols, ascorbic acid and retinol in well-defined groups of healthy, non-smokers, aged 25-45 years, 175 men and 174 women from five European countries (France, UK (Northern Ireland), Republic of Ireland, The Netherlands and Spain). Analysis was centralised and performed within 18 months. Within-gender, vitamin C showed no significant differences between centres. Females in France, Republic of Ireland and Spain had significantly higher plasma vitamin C concentrations than their male counterparts. Serum retinol and alpha-tocopherol levels were similar between centres, but gamma-tocopherol showed a great variability being the lowest in Spain and France, and the highest in The Netherlands. The provitamin A: non-provitamin A carotenoid ratio was similar among countries, whereas the xanthophylls (lutein, zeaxanthin, beta-cryptoxanthin) to carotenes (alpha-carotene, beta-carotene, lycopene) ratio was double in southern (Spain) compared to the northern areas (Northern Ireland and Republic of Ireland). Serum concentrations of lutein and zeaxanthin were highest in France and Spain; beta-cryptoxanthin was highest in Spain and The Netherlands; trans-lycopene tended to be highest in Irish males and lowest in Spanish males; alpha-carotene and beta-carotene were higher in the French volunteers. Due to the study design, the concentrations of carotenoids and vitamins A, C and E represent physiological ranges achievable by dietary means and may be considered as 'reference values' in serum of healthy, non-smoking middle-aged subjects from five European countries. The results suggest that lutein (and zeaxanthin), beta-cryptoxanthin, total xanthophylls and gamma-tocopherol (and alpha- : gamma-tocopherol) may be important markers related to the healthy or protective effects of the Mediterranean-like diet.

BACKGROUND:The analysis of red cell folate (RCF) depends on complete hemolysis of erythrocytes, and it is assumed that complete hemolysis is achieved by 10-fold dilution of whole blood with hypotonic solutions of 10 g/L ascorbic acid/ascorbate. This report challenges this assumption.METHODS:The conventional method of erythrocyte lysis was modified to include saponin, a known effective hemolyzing agent. The influence of saponin was determined at various lysate pHs, using the microbiological (Lactobacillus rhamnosus) folate assay. The effect of saponin during lysate preparation was subsequently compared with either the effect of 30 s of sonication or a single 1-h freeze-thaw cycle.RESULTS:Saponin addition was found to increase assayable RCF up to ninefold, depending on lysate pH. Sonication of lysates had no effect, and freezing-thawing lysates once did not always guarantee complete hemolysis. Lysates created with 10 g/L ascorbic acid (a historically widely used diluent) without pH adjustment produced assayable folate concentrations significantly lower than optimal.CONCLUSIONS:A lysing agent should be incorporated into RCF assays to guarantee complete hemolysis. Ten-fold dilution of blood with 10 g/L ascorbic acid, without pH adjustment, produces lysates with pHs (pH 4.0) below the point (pH 4.7) at which hemoglobin can denature irreversibly. The optimum pH for hemolysates is approximately 5.0.

It has been suggested that dietary carotenoids can enhance immune function. Supplementation with beta-carotene (15 mg daily) was previously shown to enhance human monocyte function. To examine the effect of other dietary carotenoids, two similar independent studies were done. Healthy adult male nonsmokers were randomly assigned to receive lycopene (study 1), lutein (study 2), or placebo for 26 days, followed by the alternative treatment for another 26 days. The expression of functionally related monocyte surface molecules was quantified by laser flow cytometry before and after each treatment period, There was a significant increase in plasma levels of each carotenoid following dietary supplementation, but the effects on monocyte surface molecule expression were not as striking as those observed after beta-carotene supplementation. These findings emphasize that it cannot be assumed that the effect of one carotenoid will be the same as another, even at the same level of intake.

Objectives: Application of a HPLC (high performance liquid chromatography) method, using cyanide derivatisation, to the determination of plasma pyridoxal-5-phosphate (PLP) concentrations as an indicator of vitamin B6 adequacy. Setting: The study was performed at the Institute of Food Research, Norwich, UK. Blood samples were taken at the Institute, at Health Centres, or in the volunteer’s home. Subjects: 51 adolescent, 131 adult, 68 non-institutionalized elderly and 44 aged (>73 y) volunteers were recruited from local authority schools, local Health Centres and General Practitioners. Results: The mean PLP recovery was 92.8%. The intra- and inter-assay coefficients of variation were 2.8% and 5.2% respectively. Mean PLP concentrations for males and females, respectively, were: adolescents (13–14 y), 36.4 and 43.5 nM; adults (20–64 y), 39.2 and 40.0 nM; elderly (68–73 y), 34.8 and 35.3 nM; aged (>73 y), 57.8 and 49.0 nM. Percentages of subjects with PLP concentrations <34.4 nM were over 26% in all population groups. Mean vitamin B6 intakes (μg/g protein intake), as assessed by weighed dietary records, were all above reference nutrient intakes (15 μg/g protein). Conclusions: An HPLC method, using cyanide derivitisation, has been applied to the determination of plasma PLP. Comparisons of results for local population groups with current cut-off values for plasma PLP, show large numbers of volunteers at risk of vitamin B6 deficiency although this is not reflected by vitamin B6 intakes calculated from food tables. The 34.4 nM cut-off value for value for plasma PLP, indicating deficiency, is questioned. Sponsorship: UK Ministry of Agriculture, Fisheries and Food; Department of Education and Science; Vitamin Forum.

Polyunsaturated fatty acids (PUFAs) are highly susceptible to free radical attack. In vitro studies of carotenoids--including beta-carotene, lycopene, and lutein--have shown them to be effective quenchers of singlet oxygen, to have good radical-trapping properties, or to be effective peroxyl radical scavengers (or to have a combination of these qualities). If carotenoids act as antioxidants in vivo, then arguably, plasma PUFA should be conserved. The objective of the current study was to answer the question "Does supplementation with beta-carotene, lycopene, or lutein, at dietarily achievable levels, over a time period known to significantly increase circulating carote concentrations, lead to an observable increase in fasting plasma PUFA?" The normal diets of human volunteers were supplemented with either 15 mg/day beta-carotene (n = 25), lycopene (n = 23), or lutein (n = 21) for 26 days in three independent double-blind, placebo-controlled supplementation studies. Supplementation with beta-carotene increased plasma linoleic acid but left the polyunsaturated:saturated (P:S) fatty acid ratio unaltered. In contrast, supplementation with lycopene reduced linoleic acid, which resulted in a large decrease in the P:S ratio. Lutein supplementation had no effect. It was concluded that neither beta-carotene, lycopene, nor lutein supplementation engender antioxidant effects that lead to the widespread general conservation of plasma PUFAs. Beta-carotene and lycopene supplementation appear to interact with the metabolism of linoleic acid, the "essential" fatty acid, resulting in either an increase (beta-carotene) or decrease (lycopene) in its plasma concentration. Alterations in plasma 18:2 or P:S ratios could ultimately lead to changes in tissue cellular membrane composition and hence to alterations in membrane fluidity and cell-surface protein expression.

Neural tube defects can be prevented by adequate intake of periconceptional folate, and inverse associations between folate status and cardiovascular disease and various cancers have been noted. Thus, there is renewed interest in the analysis of red cell folate (RCF) as an indicator of folate deficiency risk. Assessment of the assumptions that underpin RCF assays indicates that many are false. Published literature suggests that increased deoxy-hemoglobin (which can bind RCF electrostatically) yields more assayable folate, and increased oxy-hemoglobin (which cannot bind RCF) yields less assayable folate. It is argued that as deoxy-hemoglobin picks up oxygen and switches quaternary structure, any bound folate must, on purely theoretical grounds, become physically "trapped". Venous blood taken for analysis is 65% to 75% saturated with oxygen, and pro-rata "trapping" will lead to serious underestimation of RCF. Hence, doubt is cast over the validity of all previous RCF values. Some strategies for accurately assessing RCF are suggested.

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 B 6 (pyridoxal-5-phosphate), folate and vitamin B 12 , 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, asmall 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 B 6 (42%; 47%) and riboflavin (77%; 79%) deficiency. It was concluded that the requirements of the elderly for vitamins B 1 , B 2 and C, and the biochemical deficiency threshold vahes used to indicate vitamin B 6 deficiency, need review

Authors' reply SIR—Anthony Wright makes too much of our data when he suggests that non-pregnant women homozygous for the TT variant can be identified by red-cell folate alone. Although the variant predisposes to lower concentrations of red-cell folate, as our report shows, the eventual concentration will depend on a person's dietary intake; we found a strong correlation between plasma folate and red-cell folate in all participants, even if they are TT homozygotes. Thus, women homozygous for the thermolabile (TT) variant but on a high folate intake would be missed in a screening programme based on red-cell folate concentrations, whereas women without the variant but with a very low folate intake or undiagnosed deficiency might be included as TT homozygotes. Screening the population for this variant would not be an effective public-health measure. Homozygosity for the variant is an important risk factor for spina bifida, but accounts for only 13% of the population attributable risk. However, since mothers are one generation away from the affected offspring, folic-acid supplementation would have to be recommended if screening showed that both parents had at least one copy of the variant. In addition, up to three-quarters of neural-tube defects can be prevented by prophylactic folic acid, so, even if both parents have the wild-type genotype, supplementation would still be necessary to prevent most cases of neural-tube defects. Wright has mistakenly interpreted our 95% CI of the mean to represent about 95% of the full dataset. His calculations and assumptions regarding our methodology are not valid. Our data are not normally distributed, having a small number of very high values, which is what one expects in any normal population in which up to 10% may be taking some vitamin supplements. For example, our raw data for the group of non-pregnant women who were homozygous wild-types have a mean red-cell folate value of 381 (SD 185) g/L and a range from 144 μg/L to 1402 $ mJg/L. We agree that methods to measure plasma and red-cell folates show an unacceptably wide variation, but participation in a properly organised quality-control system (one of which is available in the UK) is more important at this time than modified or new assays. We thank S Daly, A S Whitehead, D Ramsbottom, and M R Conley for their contribution. Accurate red-cell folate analysisAnne Molloy and colleagues (May 31, p 1591)1 note association of a thermolabile variant of 5,10-methylenetetrahydrofolate reductase (C677T MTHFR) with low red-cell folate concentrations, suggesting that the thermolabile MTHFR variant creates an additional requirement for folate. Since, within the same community, the risk of neural-tube defects is inversely associated with red-cell folate concentrations in a continuous dose-response relation,2 the implication is that individuals homozygous for the C677T MTHFR variant are at increased risk of producing offspring with neural-tube defects. Full-Text PDF

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Conference Article| August 01 1996 Dietary beta-carotene supplementation modulates the production of tumour necrosis factor-α by human monocytes DAVID A. HUGHES; DAVID A. HUGHES 1Department of Nutrition, Diet and Health, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. Search for other works by this author on: This Site PubMed Google Scholar PAUL M. FINGLAS; PAUL M. FINGLAS 1Department of Nutrition, Diet and Health, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. Search for other works by this author on: This Site PubMed Google Scholar ANTHONY J.A. WRIGHT; ANTHONY J.A. WRIGHT 1Department of Nutrition, Diet and Health, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. Search for other works by this author on: This Site PubMed Google Scholar ABIGAEL C.J. PEERLESS; ABIGAEL C.J. PEERLESS 1Department of Nutrition, Diet and Health, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. Search for other works by this author on: This Site PubMed Google Scholar ANGELA L. BAILEY; ANGELA L. BAILEY 1Department of Nutrition, Diet and Health, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. Search for other works by this author on: This Site PubMed Google Scholar SIAN B. ASTLEY; SIAN B. ASTLEY 1Department of Nutrition, Diet and Health, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. Search for other works by this author on: This Site PubMed Google Scholar SUSAN SOUTHON SUSAN SOUTHON 1Department of Nutrition, Diet and Health, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, U.K. Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1996) 24 (3): 387S. https://doi.org/10.1042/bst024387s Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn MailTo Cite Icon Cite Get Permissions Citation DAVID A. HUGHES, PAUL M. FINGLAS, ANTHONY J.A. WRIGHT, ABIGAEL C.J. PEERLESS, ANGELA L. BAILEY, SIAN B. ASTLEY, SUSAN SOUTHON; Dietary beta-carotene supplementation modulates the production of tumour necrosis factor-α by human monocytes. Biochem Soc Trans 1 August 1996; 24 (3): 387S. doi: https://doi.org/10.1042/bst024387s Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search Keywords: FCS, fetal calf serum, Grp, Group, LPS, lipopolysaccharide, TNF, tumour necrosis factor-α This content is only available as a PDF. © 1996 Biochemical Society1996 Article PDF first page preview Close Modal You do not currently have access to this content.