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Ahmed El-sohemy - One of the best experts on this subject based on the ideXlab platform.

  • Haptoglobin genotype modifies the association between Dietary vitamin C and serum ascorbic acid deficiency
    The American journal of clinical nutrition, 2010
    Co-Authors: Leah E. Cahill, Ahmed El-sohemy
    Abstract:

    Background: Haptoglobin (which is encoded by the Hp gene) is a hemoglobin-binding protein that has antioxidant properties and a common polymorphism that consists of 2 structurally different alleles: Hp1 and Hp2. The capacity of Hp2 to inhibit oxidation and vitamin C depletion is less than that of Hp1, but the influence on vitamin C requirements remains unknown. Objective: This study aimed to determine whether the Hp polymorphism modifies the association between Dietary vitamin C and serum ascorbic acid deficiency (,11 lmol/L). Design: Nonsmoking men and women (n = 1046) between 20 and 29 y of age participated in the Toronto Nutrigenomics and Health Study. Blood samples were collected after the subjects had fasted overnight to determine serum ascorbic acid concentrations by HPLC and for genotyping. A 196-item food-frequency questionnaire was used to estimate vitamin C intake. Results: A gene-diet interaction on serum ascorbic acid was observed (P = 0.02). The overall odds ratio (95% CI) for serum ascorbic acid deficiency was 2.84 (1.73, 4.65) for subjects who did not meet the Recommended Dietary Allowance for vitamin C compared with those who did. The corresponding odds ratios were 4.77 (2.36, 9.65) for the Hp2‐2 genotype and 1.69 (0.80, 3.63) for carriers of the Hp1 allele. Conclusions: Individuals with the Hp2‐2 genotype had an increased risk of deficiency if they did not meet the Recommended Dietary Allowance for vitamin C, whereas carriers of the Hp1 allele did not. The findings suggest that the greater antioxidant capacity of Hp1 might spare serum ascorbic acid. Am J Clin Nutr 2010;92:1494‐500.

  • Functional genetic variants of glutathione S-transferase protect against serum ascorbic acid deficiency
    The American journal of clinical nutrition, 2009
    Co-Authors: Leah E. Cahill, Bénédicte Fontaine-bisson, Ahmed El-sohemy
    Abstract:

    Background: Glutathione S-transferases (GSTs) are detoxifying enzymes that contribute to the glutathione-ascorbic acid (vitamin C) antioxidant cycle. Objective: The objective was to determine whether GST genotypes modify the association between Dietary vitamin C and serum ascorbic acid. Design: Nonsmoking men and women (n = 905) between 20 and 29 y of age were participants in the Toronto Nutrigenomics and Health Study. Overnight fasting blood samples were collected to determine serum ascorbic acid concentrations by HPLC and to genotype for deletion polymorphisms in GSTM1 and GSTT1 and an Ile105Val substitution in GSTP1. A 196-item food-frequency questionnaire was used to estimate vitamin C intake. Results: A gene-diet interaction on serum ascorbic acid was observed for GSTM1 (P = 0.04) and GSTT1 (P = 0.01) but not for GSTP1 (P = 0.83). The odds ratio (95% CI) for serum ascorbic acid deficiency (,11 lmol/L) was 3.20 (1.88, 5.44) for subjects who did not meet the Recommended Dietary Allowance of vitamin C compared with those who did. The corresponding odds ratios (95% CIs) were 2.17 (1.10, 4.28) and 12.28 (4.26, 33.42), respectively, for individuals with the GSTT1*1/*1 +*1/*0 (functional) and GSTT1*0/*0 (null) genotypes and 2.29 (0.96, 5.45) and 4.03 (2.01, 8.09), respectively, for the GSTM1*1/*1+GSTM1*1/*0 and GSTM1*0/*0 genotypes. Conclusions: The Recommended intake of vitamin C protects against serum ascorbic acid deficiency, regardless of genotype. Individuals with GST null genotypes had an increased risk of deficiency if they did not meet the Recommended Dietary Allowance for vitamin C, which suggests that the GST enzymes protect against serum ascorbic acid deficiency when Dietary vitamin C is insufficient. Am J Clin Nutr 2009;90:1411‐7.

Leah E. Cahill - One of the best experts on this subject based on the ideXlab platform.

  • Haptoglobin genotype modifies the association between Dietary vitamin C and serum ascorbic acid deficiency
    The American journal of clinical nutrition, 2010
    Co-Authors: Leah E. Cahill, Ahmed El-sohemy
    Abstract:

    Background: Haptoglobin (which is encoded by the Hp gene) is a hemoglobin-binding protein that has antioxidant properties and a common polymorphism that consists of 2 structurally different alleles: Hp1 and Hp2. The capacity of Hp2 to inhibit oxidation and vitamin C depletion is less than that of Hp1, but the influence on vitamin C requirements remains unknown. Objective: This study aimed to determine whether the Hp polymorphism modifies the association between Dietary vitamin C and serum ascorbic acid deficiency (,11 lmol/L). Design: Nonsmoking men and women (n = 1046) between 20 and 29 y of age participated in the Toronto Nutrigenomics and Health Study. Blood samples were collected after the subjects had fasted overnight to determine serum ascorbic acid concentrations by HPLC and for genotyping. A 196-item food-frequency questionnaire was used to estimate vitamin C intake. Results: A gene-diet interaction on serum ascorbic acid was observed (P = 0.02). The overall odds ratio (95% CI) for serum ascorbic acid deficiency was 2.84 (1.73, 4.65) for subjects who did not meet the Recommended Dietary Allowance for vitamin C compared with those who did. The corresponding odds ratios were 4.77 (2.36, 9.65) for the Hp2‐2 genotype and 1.69 (0.80, 3.63) for carriers of the Hp1 allele. Conclusions: Individuals with the Hp2‐2 genotype had an increased risk of deficiency if they did not meet the Recommended Dietary Allowance for vitamin C, whereas carriers of the Hp1 allele did not. The findings suggest that the greater antioxidant capacity of Hp1 might spare serum ascorbic acid. Am J Clin Nutr 2010;92:1494‐500.

  • Functional genetic variants of glutathione S-transferase protect against serum ascorbic acid deficiency
    The American journal of clinical nutrition, 2009
    Co-Authors: Leah E. Cahill, Bénédicte Fontaine-bisson, Ahmed El-sohemy
    Abstract:

    Background: Glutathione S-transferases (GSTs) are detoxifying enzymes that contribute to the glutathione-ascorbic acid (vitamin C) antioxidant cycle. Objective: The objective was to determine whether GST genotypes modify the association between Dietary vitamin C and serum ascorbic acid. Design: Nonsmoking men and women (n = 905) between 20 and 29 y of age were participants in the Toronto Nutrigenomics and Health Study. Overnight fasting blood samples were collected to determine serum ascorbic acid concentrations by HPLC and to genotype for deletion polymorphisms in GSTM1 and GSTT1 and an Ile105Val substitution in GSTP1. A 196-item food-frequency questionnaire was used to estimate vitamin C intake. Results: A gene-diet interaction on serum ascorbic acid was observed for GSTM1 (P = 0.04) and GSTT1 (P = 0.01) but not for GSTP1 (P = 0.83). The odds ratio (95% CI) for serum ascorbic acid deficiency (,11 lmol/L) was 3.20 (1.88, 5.44) for subjects who did not meet the Recommended Dietary Allowance of vitamin C compared with those who did. The corresponding odds ratios (95% CIs) were 2.17 (1.10, 4.28) and 12.28 (4.26, 33.42), respectively, for individuals with the GSTT1*1/*1 +*1/*0 (functional) and GSTT1*0/*0 (null) genotypes and 2.29 (0.96, 5.45) and 4.03 (2.01, 8.09), respectively, for the GSTM1*1/*1+GSTM1*1/*0 and GSTM1*0/*0 genotypes. Conclusions: The Recommended intake of vitamin C protects against serum ascorbic acid deficiency, regardless of genotype. Individuals with GST null genotypes had an increased risk of deficiency if they did not meet the Recommended Dietary Allowance for vitamin C, which suggests that the GST enzymes protect against serum ascorbic acid deficiency when Dietary vitamin C is insufficient. Am J Clin Nutr 2009;90:1411‐7.

Mark Levine - One of the best experts on this subject based on the ideXlab platform.

  • A new Recommended Dietary Allowance of vitamin C for healthy young women
    Proceedings of the National Academy of Sciences of the United States of America, 2001
    Co-Authors: Mark Levine, Yaohui Wang, Sebastian J. Padayatty, Jason D. Morrow
    Abstract:

    The recently released Recommended Dietary Allowance of vitamin C for women, 75 mg daily, was based on data for men. We now report results of a depletion–repletion study with healthy young women hospitalized for 186 +/− 28 days, using vitamin C doses of 30–2,500 mg daily. The relationship between dose and steady-state plasma concentration was sigmoidal. Only doses above 100 mg were beyond the linear portion of the curve. Plasma and circulating cells saturated at 400 mg daily, with urinary elimination of higher doses. Biomarkers of endogenous oxidant stress, plasma and urine F2-isoprostanes, and urine levels of a major metabolite of F2-isoprostanes were unchanged by vitamin C at all doses, suggesting this vitamin does not alter endogenous lipid peroxidation in healthy young women. By using Food and Nutrition Board guidelines, the data indicate that the Recommended Dietary Allowance for young women should be increased to 90 mg daily.

  • Vitamin C pharmacokinetics in healthy volunteers: evidence for a Recommended Dietary Allowance.
    Proceedings of the National Academy of Sciences of the United States of America, 1996
    Co-Authors: Mark Levine, Yaohui Wang, Cathy Conry-cantilena, R W Welch, Philip W. Washko, K R Dhariwal, Jae B. Park, Alexander Lazarev, James F. Graumlich, Jean King
    Abstract:

    Abstract Determinants of the Recommended Dietary Allowance (RDA) for vitamin C include the relationship between vitamin C dose and steady-state plasma concentration, bioavailability, urinary excretion, cell concentration, and potential adverse effects. Because current data are inadequate, an in-hospital depletion-repletion study was conducted. Seven healthy volunteers were hospitalized for 4-6 months and consumed a diet containing

  • vitamin c pharmacokinetics in healthy volunteers evidence for a Recommended Dietary Allowance
    Proceedings of the National Academy of Sciences of the United States of America, 1996
    Co-Authors: Mark Levine, Yaohui Wang, R W Welch, Philip W. Washko, K R Dhariwal, Jae B. Park, Alexander Lazarev, James F. Graumlich, Cathy Conrycantilena, Jean King
    Abstract:

    Abstract Determinants of the Recommended Dietary Allowance (RDA) for vitamin C include the relationship between vitamin C dose and steady-state plasma concentration, bioavailability, urinary excretion, cell concentration, and potential adverse effects. Because current data are inadequate, an in-hospital depletion-repletion study was conducted. Seven healthy volunteers were hospitalized for 4-6 months and consumed a diet containing <5 mg of vitamin C daily. Steady-state plasma and tissue concentrations were determined at seven daily doses of vitamin C from 30 to 2500 mg. Vitamin C steady-state plasma concentrations as a function of dose displayed sigmoid kinetics. The steep portion of the curve occurred between the 30- and 100-mg daily dose, the current RDA of 60 mg daily was on the lower third of the curve, the first dose beyond the sigmoid portion of the curve was 200 mg daily, and complete plasma saturation occurred at 1000 mg daily. Neutrophils, monocytes, and lymphocytes saturated at 100 mg daily and contained concentrations at least 14-fold higher than plasma. Bioavailability was complete for 200 mg of vitamin C as a single dose. No vitamin C was excreted in urine of six of seven volunteers until the 100-mg dose. At single doses of 500 mg and higher, bioavailability declined and the absorbed amount was excreted. Oxalate and urate excretion were elevated at 1000 mg of vitamin C daily compared to lower doses. Based on these data and Institute of Medicine criteria, the current RDA of 60 mg daily should be increased to 200 mg daily, which can be obtained from fruits and vegetables. Safe doses of vitamin C are less than 1000 mg daily, and vitamin C daily doses above 400 mg have no evident value.

Jean King - One of the best experts on this subject based on the ideXlab platform.

  • Vitamin C pharmacokinetics in healthy volunteers: evidence for a Recommended Dietary Allowance.
    Proceedings of the National Academy of Sciences of the United States of America, 1996
    Co-Authors: Mark Levine, Yaohui Wang, Cathy Conry-cantilena, R W Welch, Philip W. Washko, K R Dhariwal, Jae B. Park, Alexander Lazarev, James F. Graumlich, Jean King
    Abstract:

    Abstract Determinants of the Recommended Dietary Allowance (RDA) for vitamin C include the relationship between vitamin C dose and steady-state plasma concentration, bioavailability, urinary excretion, cell concentration, and potential adverse effects. Because current data are inadequate, an in-hospital depletion-repletion study was conducted. Seven healthy volunteers were hospitalized for 4-6 months and consumed a diet containing

  • vitamin c pharmacokinetics in healthy volunteers evidence for a Recommended Dietary Allowance
    Proceedings of the National Academy of Sciences of the United States of America, 1996
    Co-Authors: Mark Levine, Yaohui Wang, R W Welch, Philip W. Washko, K R Dhariwal, Jae B. Park, Alexander Lazarev, James F. Graumlich, Cathy Conrycantilena, Jean King
    Abstract:

    Abstract Determinants of the Recommended Dietary Allowance (RDA) for vitamin C include the relationship between vitamin C dose and steady-state plasma concentration, bioavailability, urinary excretion, cell concentration, and potential adverse effects. Because current data are inadequate, an in-hospital depletion-repletion study was conducted. Seven healthy volunteers were hospitalized for 4-6 months and consumed a diet containing <5 mg of vitamin C daily. Steady-state plasma and tissue concentrations were determined at seven daily doses of vitamin C from 30 to 2500 mg. Vitamin C steady-state plasma concentrations as a function of dose displayed sigmoid kinetics. The steep portion of the curve occurred between the 30- and 100-mg daily dose, the current RDA of 60 mg daily was on the lower third of the curve, the first dose beyond the sigmoid portion of the curve was 200 mg daily, and complete plasma saturation occurred at 1000 mg daily. Neutrophils, monocytes, and lymphocytes saturated at 100 mg daily and contained concentrations at least 14-fold higher than plasma. Bioavailability was complete for 200 mg of vitamin C as a single dose. No vitamin C was excreted in urine of six of seven volunteers until the 100-mg dose. At single doses of 500 mg and higher, bioavailability declined and the absorbed amount was excreted. Oxalate and urate excretion were elevated at 1000 mg of vitamin C daily compared to lower doses. Based on these data and Institute of Medicine criteria, the current RDA of 60 mg daily should be increased to 200 mg daily, which can be obtained from fruits and vegetables. Safe doses of vitamin C are less than 1000 mg daily, and vitamin C daily doses above 400 mg have no evident value.

Yaohui Wang - One of the best experts on this subject based on the ideXlab platform.

  • A new Recommended Dietary Allowance of vitamin C for healthy young women
    Proceedings of the National Academy of Sciences of the United States of America, 2001
    Co-Authors: Mark Levine, Yaohui Wang, Sebastian J. Padayatty, Jason D. Morrow
    Abstract:

    The recently released Recommended Dietary Allowance of vitamin C for women, 75 mg daily, was based on data for men. We now report results of a depletion–repletion study with healthy young women hospitalized for 186 +/− 28 days, using vitamin C doses of 30–2,500 mg daily. The relationship between dose and steady-state plasma concentration was sigmoidal. Only doses above 100 mg were beyond the linear portion of the curve. Plasma and circulating cells saturated at 400 mg daily, with urinary elimination of higher doses. Biomarkers of endogenous oxidant stress, plasma and urine F2-isoprostanes, and urine levels of a major metabolite of F2-isoprostanes were unchanged by vitamin C at all doses, suggesting this vitamin does not alter endogenous lipid peroxidation in healthy young women. By using Food and Nutrition Board guidelines, the data indicate that the Recommended Dietary Allowance for young women should be increased to 90 mg daily.

  • Vitamin C pharmacokinetics in healthy volunteers: evidence for a Recommended Dietary Allowance.
    Proceedings of the National Academy of Sciences of the United States of America, 1996
    Co-Authors: Mark Levine, Yaohui Wang, Cathy Conry-cantilena, R W Welch, Philip W. Washko, K R Dhariwal, Jae B. Park, Alexander Lazarev, James F. Graumlich, Jean King
    Abstract:

    Abstract Determinants of the Recommended Dietary Allowance (RDA) for vitamin C include the relationship between vitamin C dose and steady-state plasma concentration, bioavailability, urinary excretion, cell concentration, and potential adverse effects. Because current data are inadequate, an in-hospital depletion-repletion study was conducted. Seven healthy volunteers were hospitalized for 4-6 months and consumed a diet containing

  • vitamin c pharmacokinetics in healthy volunteers evidence for a Recommended Dietary Allowance
    Proceedings of the National Academy of Sciences of the United States of America, 1996
    Co-Authors: Mark Levine, Yaohui Wang, R W Welch, Philip W. Washko, K R Dhariwal, Jae B. Park, Alexander Lazarev, James F. Graumlich, Cathy Conrycantilena, Jean King
    Abstract:

    Abstract Determinants of the Recommended Dietary Allowance (RDA) for vitamin C include the relationship between vitamin C dose and steady-state plasma concentration, bioavailability, urinary excretion, cell concentration, and potential adverse effects. Because current data are inadequate, an in-hospital depletion-repletion study was conducted. Seven healthy volunteers were hospitalized for 4-6 months and consumed a diet containing <5 mg of vitamin C daily. Steady-state plasma and tissue concentrations were determined at seven daily doses of vitamin C from 30 to 2500 mg. Vitamin C steady-state plasma concentrations as a function of dose displayed sigmoid kinetics. The steep portion of the curve occurred between the 30- and 100-mg daily dose, the current RDA of 60 mg daily was on the lower third of the curve, the first dose beyond the sigmoid portion of the curve was 200 mg daily, and complete plasma saturation occurred at 1000 mg daily. Neutrophils, monocytes, and lymphocytes saturated at 100 mg daily and contained concentrations at least 14-fold higher than plasma. Bioavailability was complete for 200 mg of vitamin C as a single dose. No vitamin C was excreted in urine of six of seven volunteers until the 100-mg dose. At single doses of 500 mg and higher, bioavailability declined and the absorbed amount was excreted. Oxalate and urate excretion were elevated at 1000 mg of vitamin C daily compared to lower doses. Based on these data and Institute of Medicine criteria, the current RDA of 60 mg daily should be increased to 200 mg daily, which can be obtained from fruits and vegetables. Safe doses of vitamin C are less than 1000 mg daily, and vitamin C daily doses above 400 mg have no evident value.