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Robert P Heaney - One of the best experts on this subject based on the ideXlab platform.

  • Calcium Absorption and bone mineral density in celiacs after long term treatment with gluten free diet and adequate Calcium intake
    Osteoporosis International, 2005
    Co-Authors: Michael Pazianas, Robert P Heaney, G P Butcher, J Subhani, P J Finch, L Ang, C Collins, Mone Zaidi, J D Maxwell
    Abstract:

    Calcium malAbsorption, hypocalcemia and skeletal demineralization are well-recognized features of untreated celiac disease. This study investigates Calcium Absorption and bone mineral density (BMD) after a prolonged, over 4 years, treatment with a gluten-free diet. Twenty-four adult females with treated celiac disease and twenty age- and sex-matched control subjects were studied. Mean body mass index (MBI), energy intake, serum Calcium, and serum 25(OH)D concentrations in treated celiacs did not differ from controls. However, while both dietary Calcium and protein intake were significantly higher in celiacs (P<0.012), fractional Calcium Absorption was lower (mean percentage±SD; treated 39.8±12 versus controls 52.3±10, P<0.001). Thus, after adjusting for Calcium intake, the estimated amount of Calcium absorbed daily was similar in both groups. Whole body, spine and trochanter BMD were significantly lower in treated celiac patients compared with controls (P<0.05). There were significant inverse correlations between: serum parathyroid hormone (PTH) and femoral neck or total body BMD (P<0.01), PTH and duration of gluten-free diet (P=0.05), and fractional Calcium Absorption and alkaline phosphatase (P=0.022). Increased Calcium intake could potentially compensate for the reduced fractional Calcium Absorption in treated adult celiac patients, but may not normalize the BMD. In addition, the inverse correlation between PTH and time following treatment is suggestive of a continuing long-term benefit of gluten withdrawal on bone metabolism in celiac patients.

  • enriched chicory inulin increases Calcium Absorption mainly in girls with lower Calcium Absorption
    Nutrition Research, 2003
    Co-Authors: Ian J Griffin, Robert P Heaney, Penni D Hicks, Steven A Abrams
    Abstract:

    Abstract We have previously shown that consumption of modest amounts of Synergy1 (long-chain inulin enriched with oligofructose) significantly increases Calcium Absorption in girls. The objective of this study was to determine which subject characteristics are associated with this beneficial effect. Data from our original cohort of 29 girls were combined with those of an additional 25 newly recruited subjects. Calcium Absorption was measured twice, in random order, after 3 weeks’ adaptation to either 8 g/d Synergy1 or placebo (sucrose), separated by a 2-week washout period, using a dual-tracer stable isotope method. Overall, Synergy1 significantly increased Calcium Absorption from 33.1% (SD 9.2%) to 36.1% (SD 9.8%, p = 0.027). The most consistent identifiable determinant of a beneficial effect of Synergy1 on Calcium Absorption was the fractional Calcium Absorption during the placebo period, with those individuals with lower Calcium Absorption during the placebo period showing the greatest benefit. Abbreviations: C, Caucasian; H, Hispanic; AA, African American.

  • Calcium Absorption varies within the reference range for serum 25 hydroxyvitamin d
    Journal of The American College of Nutrition, 2003
    Co-Authors: Robert P Heaney, Susan M Dowell, Cecilia A Hale, Adrianne Bendich
    Abstract:

    Background: Calcium Absorption is generally considered to be impaired under conditions of vitamin D deficiency, but the vitamin D status that fully normalizes Absorption is not known for humans.Objective: To quantify Calcium Absorption at two levels of vitamin D repletion, using pharmacokinetic methods and commercially marketed Calcium supplements.Design: Two experiments performed in the spring of the year, one year apart. In the first, in which participants were pretreated with 25-hydroxyvitamin D (25OHD), mean serum 25OHD concentration was 86.5 nmol/L; and in the other, with no pretreatment, mean serum concentration was 50.2 nmol/L. Participants received 500 mg oral Calcium loads as a part of a standard low Calcium breakfast. A low Calcium lunch was provided at mid-day. Blood was obtained fasting and at frequent intervals for 10 to 12 hours thereafter.Methods: Relative Calcium Absorption at the two 25OHD concentrations was estimated from the area under the curve (AUC) for the load-induced increment in s...

  • effects of above average summer sun exposure on serum 25 hydroxyvitamin d and Calcium Absorption
    The Journal of Clinical Endocrinology and Metabolism, 2002
    Co-Authors: Janet M Bargerlux, Robert P Heaney
    Abstract:

    The purpose of this study was to examine the effects of summer sun exposure on serum 25-hydroxyvitamin D [25(OH)D], Calcium Absorption fraction, and urinary Calcium excretion. Subjects were 30 healthy men who had just completed a summer season of extended outdoor activity (e.g. landscaping, construction work, farming, or recreation). Twenty-six subjects completed both visits: after summer sun exposure and again approximately 175 d later, after winter sun deprivation. We characterized each subject’s sun exposure by locale, schedule, and usual attire. At both visits we measured serum 25(OH)D, fasting urinary Calcium to creatinine ratio, and Calcium Absorption fraction. Median serum 25(OH)D decreased from 122 nmol/liter in late summer to 74 nmol/liter in late winter. The median seasonal difference of 49 nmol/liter (interquartile range, 29–67) was highly significant (P < 0.0001). However, we found only a trivial, nonsignificant seasonal difference in Calcium Absorption fraction and no change in fasting urinar...

  • effects of above average summer sun exposure on serum 25 hydroxyvitamin d and Calcium Absorption
    The Journal of Clinical Endocrinology and Metabolism, 2002
    Co-Authors: Janet M Bargerlux, Robert P Heaney
    Abstract:

    The purpose of this study was to examine the effects of summer sun exposure on serum 25-hydroxyvitamin D [25(OH)D], Calcium Absorption fraction, and urinary Calcium excretion. Subjects were 30 healthy men who had just completed a summer season of extended outdoor activity (e.g. landscaping, construction work, farming, or recreation). Twenty-six subjects completed both visits: after summer sun exposure and again approximately 175 d later, after winter sun deprivation. We characterized each subject's sun exposure by locale, schedule, and usual attire. At both visits we measured serum 25(OH)D, fasting urinary Calcium to creatinine ratio, and Calcium Absorption fraction. Median serum 25(OH)D decreased from 122 nmol/liter in late summer to 74 nmol/liter in late winter. The median seasonal difference of 49 nmol/liter (interquartile range, 29-67) was highly significant (P < 0.0001). However, we found only a trivial, nonsignificant seasonal difference in Calcium Absorption fraction and no change in fasting urinary Calcium to creatinine ratio. Findings from earlier work indicate that our subjects' sun exposure was equivalent in 25(OH)D production to extended oral dosing with 70 micro g/d vitamin D(3) (interquartile range, 41-96) or, equivalently, 2800 IU/d (interquartile range, 1640-3840). Despite this input, at the late winter visit, 25(OH)D was less than 50 nmol/liter in 3 subjects and less than 75 nmol/liter in 15 subjects.

Steven A Abrams - One of the best experts on this subject based on the ideXlab platform.

  • potassium bicarbonate attenuates the urinary nitrogen excretion that accompanies an increase in dietary protein and may promote Calcium Absorption
    The Journal of Clinical Endocrinology and Metabolism, 2009
    Co-Authors: Lisa Ceglia, Susan S Harris, Helen Rasmussen, Steven A Abrams, Gerard E Dallal, Bess Dawsonhughes
    Abstract:

    Context: Protein is an essential component of muscle and bone. However, the acidic byproducts of protein metabolism may have a negative impact on the musculoskeletal system, particularly in older individuals with declining renal function. Objective: We sought to determine whether adding an alkaline salt, potassium bicarbonate (KHCO3), allows protein to have a more favorable net impact on intermediary indices of muscle and bone conservation than it does in the usual acidic environment. Design: We conducted a 41-d randomized, placebo-controlled, double-blind study of KHCO3 or placebo with a 16-d phase-in and two successive 10-d metabolic diets containing low (0.5 g/kg) or high (1.5 g/kg) protein in random order with a 5-d washout between diets. Setting: The study was conducted in a metabolic research unit. Participants: Nineteen healthy subjects ages 54–82 yr participated. Intervention: KHCO3 (up to 90 mmol/d) or placebo was administered for 41 d. Main Outcome Measures: We measured 24-h urinary nitrogen excretion, IGF-I, 24-h urinary Calcium excretion, and fractional Calcium Absorption. Results: KHCO3 reduced the rise in urinary nitrogen excretion that accompanied an increase in protein intake (P = 0.015) and was associated with higher IGF-I levels on the low-protein diet (P = 0.027) with a similar trend on the high-protein diet (P = 0.050). KHCO3 was also associated with higher fractional Calcium Absorption on the low-protein diet (P = 0.041) with a similar trend on the high-protein diet (P = 0.064). Conclusions: In older adults, KHCO3 attenuates the protein-induced rise in urinary nitrogen excretion, and this may be mediated by IGF-I. KHCO3 may also promote Calcium Absorption independent of the dietary protein content.

  • an inulin type fructan enhances Calcium Absorption primarily via an effect on colonic Absorption in humans
    Journal of Nutrition, 2007
    Co-Authors: Steven A Abrams, Ian J Griffin, Keli M Hawthorne, Penni D Hicks, Oluseyi Aliu, Zhensheng Chen
    Abstract:

    Calcium Absorption efficiency and bone mineral mass are increased in adolescents who regularly consume inulin-type fructans (ITF). The mechanism of action in increasing Absorption is unknown but may be related to increased colonic Calcium Absorption. We conducted a study in young adults designed to evaluate these mechanisms with a kinetic technique using (42)Ca orally and (46)Ca dosed i.v. Those who responded to 8 wk of supplementation with 8 g of a mixed short and long degree of polymerization ITF by increasing their Calcium Absorption had kinetic measurements analyzed to evaluate the time course of Absorption. The area under the curve of the oral tracer in the blood during the 26 h after dosing was calculated and the time dependence of increased Absorption determined. Eight young adults (of 13 studied), with mean Calcium intake approximately 900 mg/d, responded to the ITF with an increased Calcium Absorption of at least 3%. In responders, Absorption increased from 22.7 +/- 11.3% to 31.0 +/- 15.3%. Colonic Absorption, defined as Absorption that occurred >7 h after oral dosing, represented 69.6 +/- 18.6% of the increase, or 49 +/- 28 mg/d. These findings suggest that, in those who respond to ITF, its effects on Calcium Absorption occur principally in the colon. This benefit to ITF may be especially important when Absorption in the small intestine is impaired for anatomic or physiological reasons.

  • a combination of prebiotic short and long chain inulin type fructans enhances Calcium Absorption and bone mineralization in young adolescents
    The American Journal of Clinical Nutrition, 2005
    Co-Authors: Steven A Abrams, Ian J Griffin, Keli M Hawthorne, Lily K Liang, Sheila K Gunn, Gretchen J Darlington, Kenneth J Ellis
    Abstract:

    BACKGROUND Short-term studies in adolescents have generally shown an enhancement of Calcium Absorption by inulin-type fructans (prebiotics). Results have been inconsistent; however, and no studies have been conducted to determine whether this effect persists with long-term use. OBJECTIVE The objective was to assess the effects on Calcium Absorption and bone mineral accretion after 8 wk and 1 y of supplementation with an inulin-type fructan. DESIGN Pubertal adolescents were randomly assigned to receive 8 g/d of a mixed short and long degree of polymerization inulin-type fructan product (fructan group) or maltodextrin placebo (control group). Bone mineral content and bone mineral density were measured before randomization and after 1 y. Calcium Absorption was measured with the use of stable isotopes at baseline and 8 wk and 1 y after supplementation. Polymorphisms of the Fok1 vitamin D receptor gene were determined. RESULTS Calcium Absorption was significantly greater in the fructan group than in the control group at 8 wk (difference: 8.5 +/- 1.6%; P < 0.001) and at 1 y (difference: 5.9 +/- 2.8%; P = 0.04). An interaction with Fok1 genotype was present such that subjects with an ff genotype had the least initial response to fructan. After 1 y, the fructan group had a greater increment in both whole-body bone mineral content (difference: 35 +/- 16 g; P = 0.03) and whole-body bone mineral density (difference: 0.015 +/- 0.004 g/cm(2); P = 0.01) than did the control group. CONCLUSION Daily consumption of a combination of prebiotic short- and long-chain inulin-type fructans significantly increases Calcium Absorption and enhances bone mineralization during pubertal growth. Effects of dietary factors on Calcium Absorption may be modulated by genetic factors, including specific vitamin D receptor gene polymorphisms.

  • enriched chicory inulin increases Calcium Absorption mainly in girls with lower Calcium Absorption
    Nutrition Research, 2003
    Co-Authors: Ian J Griffin, Robert P Heaney, Penni D Hicks, Steven A Abrams
    Abstract:

    Abstract We have previously shown that consumption of modest amounts of Synergy1 (long-chain inulin enriched with oligofructose) significantly increases Calcium Absorption in girls. The objective of this study was to determine which subject characteristics are associated with this beneficial effect. Data from our original cohort of 29 girls were combined with those of an additional 25 newly recruited subjects. Calcium Absorption was measured twice, in random order, after 3 weeks’ adaptation to either 8 g/d Synergy1 or placebo (sucrose), separated by a 2-week washout period, using a dual-tracer stable isotope method. Overall, Synergy1 significantly increased Calcium Absorption from 33.1% (SD 9.2%) to 36.1% (SD 9.8%, p = 0.027). The most consistent identifiable determinant of a beneficial effect of Synergy1 on Calcium Absorption was the fractional Calcium Absorption during the placebo period, with those individuals with lower Calcium Absorption during the placebo period showing the greatest benefit. Abbreviations: C, Caucasian; H, Hispanic; AA, African American.

  • non digestible oligosaccharides and Calcium Absorption in girls with adequate Calcium intakes
    British Journal of Nutrition, 2002
    Co-Authors: Ian J Griffin, P M Davila, Steven A Abrams
    Abstract:

    Non-digestible oligosaccharides such as inulin and oligofructose have been shown to consistently increase Calcium Absorption in experimental animals, but data in humans are less clear-cut. The objective of this study was to assess the effect of 8 g/d of oligofructose or a mixture of inulin and oligofructose on Calcium Absorption in girls at or near menarche. A total of fifty-nine subjects were studied using a balanced, randomized, cross-over design. They received, in random order, 8 g/d placebo (sucrose), oligofructose or the mixture inulin+oligofructose for 3 weeks, separated by a 2-week washout period. Throughout the study, subjects consumed a total of approximately 1500 mg/d dietary Calcium, by adding two glasses of Calcium-fortified orange juice to their diet. Four grams of placebo, oligofructose or the mixture inulin+oligofructose was added to each glass of orange juice immediately before it was consumed. At the end of each 3-week adaptation period, Calcium Absorption was measured, using a dual stable isotope technique, from the cumulative fractional excretion of an oral and an intravenous tracer over 48 hours. Calcium Absorption was significantly higher in the group receiving the inulin+oligofructose mixture than in the placebo group (38.2 ± 9.8 % v. 32.3 ± 9-8 %; P=0.01), but no significant difference was seen between the oligofructose group and the placebo group (318 ± 9.3 % v. 318 ± 100%, P=NS). We conclude that modest intakes of an inulin+oligofructose mixture increases Calcium Absorption in girls at or near menarche.

Ian J Griffin - One of the best experts on this subject based on the ideXlab platform.

  • an inulin type fructan enhances Calcium Absorption primarily via an effect on colonic Absorption in humans
    Journal of Nutrition, 2007
    Co-Authors: Steven A Abrams, Ian J Griffin, Keli M Hawthorne, Penni D Hicks, Oluseyi Aliu, Zhensheng Chen
    Abstract:

    Calcium Absorption efficiency and bone mineral mass are increased in adolescents who regularly consume inulin-type fructans (ITF). The mechanism of action in increasing Absorption is unknown but may be related to increased colonic Calcium Absorption. We conducted a study in young adults designed to evaluate these mechanisms with a kinetic technique using (42)Ca orally and (46)Ca dosed i.v. Those who responded to 8 wk of supplementation with 8 g of a mixed short and long degree of polymerization ITF by increasing their Calcium Absorption had kinetic measurements analyzed to evaluate the time course of Absorption. The area under the curve of the oral tracer in the blood during the 26 h after dosing was calculated and the time dependence of increased Absorption determined. Eight young adults (of 13 studied), with mean Calcium intake approximately 900 mg/d, responded to the ITF with an increased Calcium Absorption of at least 3%. In responders, Absorption increased from 22.7 +/- 11.3% to 31.0 +/- 15.3%. Colonic Absorption, defined as Absorption that occurred >7 h after oral dosing, represented 69.6 +/- 18.6% of the increase, or 49 +/- 28 mg/d. These findings suggest that, in those who respond to ITF, its effects on Calcium Absorption occur principally in the colon. This benefit to ITF may be especially important when Absorption in the small intestine is impaired for anatomic or physiological reasons.

  • a combination of prebiotic short and long chain inulin type fructans enhances Calcium Absorption and bone mineralization in young adolescents
    The American Journal of Clinical Nutrition, 2005
    Co-Authors: Steven A Abrams, Ian J Griffin, Keli M Hawthorne, Lily K Liang, Sheila K Gunn, Gretchen J Darlington, Kenneth J Ellis
    Abstract:

    BACKGROUND Short-term studies in adolescents have generally shown an enhancement of Calcium Absorption by inulin-type fructans (prebiotics). Results have been inconsistent; however, and no studies have been conducted to determine whether this effect persists with long-term use. OBJECTIVE The objective was to assess the effects on Calcium Absorption and bone mineral accretion after 8 wk and 1 y of supplementation with an inulin-type fructan. DESIGN Pubertal adolescents were randomly assigned to receive 8 g/d of a mixed short and long degree of polymerization inulin-type fructan product (fructan group) or maltodextrin placebo (control group). Bone mineral content and bone mineral density were measured before randomization and after 1 y. Calcium Absorption was measured with the use of stable isotopes at baseline and 8 wk and 1 y after supplementation. Polymorphisms of the Fok1 vitamin D receptor gene were determined. RESULTS Calcium Absorption was significantly greater in the fructan group than in the control group at 8 wk (difference: 8.5 +/- 1.6%; P < 0.001) and at 1 y (difference: 5.9 +/- 2.8%; P = 0.04). An interaction with Fok1 genotype was present such that subjects with an ff genotype had the least initial response to fructan. After 1 y, the fructan group had a greater increment in both whole-body bone mineral content (difference: 35 +/- 16 g; P = 0.03) and whole-body bone mineral density (difference: 0.015 +/- 0.004 g/cm(2); P = 0.01) than did the control group. CONCLUSION Daily consumption of a combination of prebiotic short- and long-chain inulin-type fructans significantly increases Calcium Absorption and enhances bone mineralization during pubertal growth. Effects of dietary factors on Calcium Absorption may be modulated by genetic factors, including specific vitamin D receptor gene polymorphisms.

  • enriched chicory inulin increases Calcium Absorption mainly in girls with lower Calcium Absorption
    Nutrition Research, 2003
    Co-Authors: Ian J Griffin, Robert P Heaney, Penni D Hicks, Steven A Abrams
    Abstract:

    Abstract We have previously shown that consumption of modest amounts of Synergy1 (long-chain inulin enriched with oligofructose) significantly increases Calcium Absorption in girls. The objective of this study was to determine which subject characteristics are associated with this beneficial effect. Data from our original cohort of 29 girls were combined with those of an additional 25 newly recruited subjects. Calcium Absorption was measured twice, in random order, after 3 weeks’ adaptation to either 8 g/d Synergy1 or placebo (sucrose), separated by a 2-week washout period, using a dual-tracer stable isotope method. Overall, Synergy1 significantly increased Calcium Absorption from 33.1% (SD 9.2%) to 36.1% (SD 9.8%, p = 0.027). The most consistent identifiable determinant of a beneficial effect of Synergy1 on Calcium Absorption was the fractional Calcium Absorption during the placebo period, with those individuals with lower Calcium Absorption during the placebo period showing the greatest benefit. Abbreviations: C, Caucasian; H, Hispanic; AA, African American.

  • non digestible oligosaccharides and Calcium Absorption in girls with adequate Calcium intakes
    British Journal of Nutrition, 2002
    Co-Authors: Ian J Griffin, P M Davila, Steven A Abrams
    Abstract:

    Non-digestible oligosaccharides such as inulin and oligofructose have been shown to consistently increase Calcium Absorption in experimental animals, but data in humans are less clear-cut. The objective of this study was to assess the effect of 8 g/d of oligofructose or a mixture of inulin and oligofructose on Calcium Absorption in girls at or near menarche. A total of fifty-nine subjects were studied using a balanced, randomized, cross-over design. They received, in random order, 8 g/d placebo (sucrose), oligofructose or the mixture inulin+oligofructose for 3 weeks, separated by a 2-week washout period. Throughout the study, subjects consumed a total of approximately 1500 mg/d dietary Calcium, by adding two glasses of Calcium-fortified orange juice to their diet. Four grams of placebo, oligofructose or the mixture inulin+oligofructose was added to each glass of orange juice immediately before it was consumed. At the end of each 3-week adaptation period, Calcium Absorption was measured, using a dual stable isotope technique, from the cumulative fractional excretion of an oral and an intravenous tracer over 48 hours. Calcium Absorption was significantly higher in the group receiving the inulin+oligofructose mixture than in the placebo group (38.2 ± 9.8 % v. 32.3 ± 9-8 %; P=0.01), but no significant difference was seen between the oligofructose group and the placebo group (318 ± 9.3 % v. 318 ± 100%, P=NS). We conclude that modest intakes of an inulin+oligofructose mixture increases Calcium Absorption in girls at or near menarche.

  • Calcium fortification of breakfast cereal enhances Calcium Absorption in children without affecting iron Absorption
    The Journal of Pediatrics, 2001
    Co-Authors: Steven A Abrams, Ian J Griffin, Penni Davila, Lily K Liang
    Abstract:

    Abstract Objectives: Provision of Calcium-fortified foods may represent an important component of improving the Calcium intake of children. We sought to determine whether the addition of Calcium to cereal would have a net positive effect on Calcium Absorption without decreasing iron Absorption. Methods: Twenty-seven children, 6 to 9 years of age, were provided two servings per day (30 g of cereal per serving) of either a low (39 mg/serving) or fortified (156 mg/serving) Calcium-containing cereal product for 14 days. Calcium Absorption was measured by using stable isotopes added to milk (extrinsically labeled) and to the Calcium-fortified cereal (intrinsically labeled). Results: Fractional Calcium Absorption from the fortified cereal was virtually identical to that from milk. Fractional Absorption of Calcium from milk did not differ significantly when given with enriched or low-Calcium-containing cereal. Total Calcium Absorption increased from 215 ± 45 mg/d to 269 ± 45 mg/d with the addition of the Calcium-fortified cereal ( P Conclusions: The addition of a moderate amount of Calcium to a cereal product was beneficial to Calcium Absorption and did not interfere with iron Absorption. Use of Calcium-fortified food products may be considered a practical approach to increasing the Calcium intake of children. (J Pediatr 2001;139:522-6)

Janet M Bargerlux - One of the best experts on this subject based on the ideXlab platform.

  • effects of above average summer sun exposure on serum 25 hydroxyvitamin d and Calcium Absorption
    The Journal of Clinical Endocrinology and Metabolism, 2002
    Co-Authors: Janet M Bargerlux, Robert P Heaney
    Abstract:

    The purpose of this study was to examine the effects of summer sun exposure on serum 25-hydroxyvitamin D [25(OH)D], Calcium Absorption fraction, and urinary Calcium excretion. Subjects were 30 healthy men who had just completed a summer season of extended outdoor activity (e.g. landscaping, construction work, farming, or recreation). Twenty-six subjects completed both visits: after summer sun exposure and again approximately 175 d later, after winter sun deprivation. We characterized each subject’s sun exposure by locale, schedule, and usual attire. At both visits we measured serum 25(OH)D, fasting urinary Calcium to creatinine ratio, and Calcium Absorption fraction. Median serum 25(OH)D decreased from 122 nmol/liter in late summer to 74 nmol/liter in late winter. The median seasonal difference of 49 nmol/liter (interquartile range, 29–67) was highly significant (P < 0.0001). However, we found only a trivial, nonsignificant seasonal difference in Calcium Absorption fraction and no change in fasting urinar...

  • effects of above average summer sun exposure on serum 25 hydroxyvitamin d and Calcium Absorption
    The Journal of Clinical Endocrinology and Metabolism, 2002
    Co-Authors: Janet M Bargerlux, Robert P Heaney
    Abstract:

    The purpose of this study was to examine the effects of summer sun exposure on serum 25-hydroxyvitamin D [25(OH)D], Calcium Absorption fraction, and urinary Calcium excretion. Subjects were 30 healthy men who had just completed a summer season of extended outdoor activity (e.g. landscaping, construction work, farming, or recreation). Twenty-six subjects completed both visits: after summer sun exposure and again approximately 175 d later, after winter sun deprivation. We characterized each subject's sun exposure by locale, schedule, and usual attire. At both visits we measured serum 25(OH)D, fasting urinary Calcium to creatinine ratio, and Calcium Absorption fraction. Median serum 25(OH)D decreased from 122 nmol/liter in late summer to 74 nmol/liter in late winter. The median seasonal difference of 49 nmol/liter (interquartile range, 29-67) was highly significant (P < 0.0001). However, we found only a trivial, nonsignificant seasonal difference in Calcium Absorption fraction and no change in fasting urinary Calcium to creatinine ratio. Findings from earlier work indicate that our subjects' sun exposure was equivalent in 25(OH)D production to extended oral dosing with 70 micro g/d vitamin D(3) (interquartile range, 41-96) or, equivalently, 2800 IU/d (interquartile range, 1640-3840). Despite this input, at the late winter visit, 25(OH)D was less than 50 nmol/liter in 3 subjects and less than 75 nmol/liter in 15 subjects.

Sylvia Christakos - One of the best experts on this subject based on the ideXlab platform.

  • vitamin d and intestinal Calcium Absorption
    Molecular and Cellular Endocrinology, 2011
    Co-Authors: Sylvia Christakos, Puneet Dhawan, Angela R Porta, Leila J Mady, Tanya Seth
    Abstract:

    The principal function of vitamin D in Calcium homeostasis is to increase Calcium Absorption from the intestine. Calcium is absorbed by both an active transcellular pathway, which is energy dependent, and by a passive paracellular pathway through tight junctions. 1,25Dihydroxyvitamin D3 (1,25(OH)2D3) the hormonally active form of vitamin D, through its genomic actions, is the major stimulator of active intestinal Calcium Absorption which involves Calcium influx, translocation of Calcium through the interior of the enterocyte and basolateral extrusion of Calcium by the intestinal plasma membrane pump. This article reviews recent studies that have challenged the traditional model of vitamin D mediated transcellular Calcium Absorption and the crucial role of specific Calcium transport proteins in intestinal Calcium Absorption. There is also increasing evidence that 1,25(OH)2D3 can enhance paracellular Calcium diffusion. The influence of estrogen, prolactin, glucocorticoids and aging on intestinal Calcium Absorption and the role of the distal intestine in vitamin D mediated intestinal Calcium Absorption are also discussed.

  • trpv6 mediates intestinal Calcium Absorption during Calcium restriction and contributes to bone homeostasis
    Bone, 2010
    Co-Authors: Liesbet Lieben, Sylvia Christakos, Roger Bouillon, Ingrid Stockmans, Bryan S Benn, Dare V Ajibade, Karen Moermans, Matthias A Hediger, Jibin Peng, Geert Carmeliet
    Abstract:

    Energy-dependent intestinal Calcium Absorption is important for the maintenance of Calcium and bone homeostasis, especially when dietary Calcium supply is restricted. The active form of vitamin D, 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], is a crucial regulator of this process and increases the expression of the transient receptor potential vanilloid 6 (Trpv6) Calcium channel that mediates Calcium transfer across the intestinal apical membrane. Genetic inactivation of Trpv6 in mice (Trpv6(-/-)) showed, however, that TRPV6 is redundant for intestinal Calcium Absorption when dietary Calcium content is normal/high and passive diffusion likely contributes to maintain normal serum Calcium levels. On the other hand, Trpv6 inactivation impaired the increase in intestinal Calcium transport following Calcium restriction, however without resulting in hypocalcemia. A possible explanation is that normocalcemia is maintained at the expense of bone homeostasis, a hypothesis investigated in this study. In this study, we thoroughly analyzed the bone phenotype of Trpv6(-/-) mice receiving a normal (approximately 1%) or low (approximately 0.02%) Calcium diet from weaning onwards using micro-computed tomography, histomorphometry and serum parameters. When dietary supply of Calcium is normal, Trpv6 inactivation did not affect growth plate morphology, bone mass and remodeling parameters in young adult or aging mice. Restricting dietary Calcium had no effect on serum Calcium levels and resulted in a comparable reduction in bone mass accrual in Trpv6(+/+) and Trpv6(-/-) mice (-35% and 45% respectively). This decrease in bone mass was associated with a similar increase in bone resorption, whereas serum osteocalcin levels and the amount of unmineralized bone matrix were only significantly increased in Trpv6(-/-) mice. Taken together, our findings indicate that TRPV6 contributes to intestinal Calcium transport when dietary Calcium supply is limited and in this condition indirectly regulates bone formation and/or mineralization.

  • trpv6 is not required for 1α 25 dihydroxyvitamin d3 induced intestinal Calcium Absorption in vivo
    Proceedings of the National Academy of Sciences of the United States of America, 2008
    Co-Authors: Galina D Kutuzova, Sylvia Christakos, Flora Sundersingh, Jennifer Vaughan, Bulli Padmaja Tadi, Susan E Ansay, Hector F Deluca
    Abstract:

    The requirement for TRPV6 for vitamin D-dependent intestinal Calcium Absorption in vivo has been examined by using vitamin D-deficient TRPV6 null mice and littermate wild-type mice. Each of the vitamin D-deficient animals received each day for 4 days 50 ng of 1,25-dihydroyvitamin D3 in 0.1 ml of 95% propylene glycol:5% ethanol vehicle or vehicle only. Both the wild-type and TRPV6 null mice responded equally well to 1,25-dihydroxyvitamin D3 in increasing intestinal Calcium Absorption. These results, along with our microarray data, demonstrate that TRPV6 is not required for vitamin D-induced intestinal Calcium Absorption and may not carry out a significant role in this process. These and previous results using calbindin D9k null mutant mice illustrate that molecular events in the intestinal Calcium Absorption process in response to the active form of vitamin D remain to be defined.

  • evidence for involvement of 17β estradiol in intestinal Calcium Absorption independent of 1 25 dihydroxyvitamin d3 level in the rat
    Journal of Bone and Mineral Research, 1999
    Co-Authors: E M Colin, Sylvia Christakos, Hector F Deluca, G J C M Van Den Bemd, M O Van Aken, H R De Jonge, Jean M Prahl, J C Birkenhager, C J Buurman, H A P Pols
    Abstract:

    The sex steroid 17β-estradiol (17β-E2) has a broad range of actions, including effects on Calcium and bone metabolism. This study with 3-month-old Brown Norway rats was designed to investigate the role of 17β-E2 in the regulation of Calcium homeostasis. Rats were divided in four groups, sham-operated, ovariectomized (OVX), and OVX supplemented with either a 0.025-mg or 0.05-mg 17β-E2 pellet implanted subcutaneously. After 4 weeks, in none of the groups was serum Calcium, phosphate, or parathyroid hormone altered compared with the sham group, while only in the OVX rats was a significant reduction in urinary Calcium found. Bone mineral density and osteocalcin were modified, as can be expected after OVX and 17β-E2 supplementation. OVX resulted in a nonsignificant increase in serum 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Supplementation with either one of the 17β-E2 dosages resulted in an 80% reduction of 1,25(OH)2D3 and only a 20% reduction in 25-hydroxyvitamin D3 levels. OVX, as well as supplementation with 17β-E2, did not affect serum levels of vitamin D binding protein. As a consequence, the estimated free 1,25(OH)2D3 levels were also significantly decreased in the 17β-E2-supplemented group compared with the sham and OVX groups. Next, the consequences for intestinal Calcium Absorption were analyzed by the in situ intestinal loop technique. Although the 1,25(OH)2D3 serum level was increased, OVX resulted in a significant decrease in intestinal Calcium Absorption in the duodenum. Despite the strongly reduced 1,25(OH)2D3 levels (18.1 ± 2.1 and 16.4 ± 2.2 pmol/l compared with 143.5 ± 29 pmol/l for the OVX group), the OVX-induced decrease in Calcium Absorption could partially be restored by supplementation with either 0.025 mg or 0.05 mg of 17β-E2. None of the treatments resulted in a significant change in Calcium handling in the jejunum, although the trends were similar as those observed in the duodenum. 17β-E2 did not change the VDR levels in both the intestine and the kidney. In conclusion, the present study demonstrates that 17β-E2 is positively involved in intestinal Calcium Absorption, and the data strengthen the assertion that 17β-E2 exerts this effect independent of 1,25(OH)2D3. In general, 17β-E2 not only affects bone turnover but also Calcium homeostasis via an effect on intestinal Calcium Absorption.