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Biomedical subjects

Steven A Abrams

Publications and source records attributed to Steven A Abrams.

At least 37 records · Page 2Linked to original sources
PubMed2004

Pubertal girls only partially adapt to low dietary calcium intakes.

UNLABELLED: We evaluated the effects of low calcium in the diets of young adolescent girls. We measured calcium absorption and excretion using stable isotopes. We found partial adaptation to low intakes but a persistent large deficit relative to recommended intakes. Low calcium intakes pose a substantial risk of inadequate calcium retention. INTRODUCTION: A substantial number of adolescent girls in the United States have habitual calcium intakes <500 mg/day (about 40% of the current recommended intake). The ability to adapt to these very low intakes by increasing calcium absorption and decreasing calcium excretion is not known. We sought to determine the effects of recommended (REC-Ca) versus very low (LO-Ca) calcium intakes on calcium absorption and excretion in white and black girls. MATERIALS AND METHODS: Pubertal, but premenarcheal girls, were adapted to low or recommended calcium intakes for at least 2 weeks before each study. Calcium absorption (n = 51) and endogenous fecal calcium excretion (n = 36 of the 51) were determined by dual-tracer stable isotope studies. Subjects were then switched to the other diet for at least 6 weeks, and the study was repeated. RESULTS: Calcium intake was 389 +/- 10 mg/day on LO-Ca and 1259 +/- 35 mg/day on REC-Ca diets. Fractional absorption increased from 44.9 +/- 1.9% on REC-Ca to 63.4 +/- 1.7% on LO-Ca (p < 0.01), but the net calcium absorption remained less than one-half the value on LO-Ca as on REC-Ca. Despite decreases in both endogenous fecal calcium excretion and urinary calcium excretion, net calcium balance was much lower on LO-Ca compared with REC-Ca1 (131 +/- 14 versus 349 +/- 32 mg/day, respectively; p < 0.001). We found significantly lower urinary calcium excretion but not calcium absorption in black girls compared with white girls. CONCLUSIONS: Very low calcium intakes are only partially adapted to by increased absorption and decreased excretion. Very low calcium intakes place both white and black pubertal girls at substantial risk for inadequate calcium retention.

Calcium↗
PubMed2004

Bioavailability of iron and zinc from a multiple micronutrient-fortified beverage.

OBJECTIVE: To test the hypothesis that micronutrient beverages can provide the daily iron and zinc needs of small children. STUDY DESIGN: Forty children aged 6 to 9 years were recruited (Lima, Peru). For 4 weeks, they received a daily serving of a beverage containing multiple micronutrients. Over 2 consecutive days, subjects received stable isotope-labeled servings of the beverage with and without a meal as well as an intravenous dose of zinc. Iron and zinc bioavailability were assessed using mass spectrometry. RESULTS: Iron absorption was significantly lower with a meal than without (9.8 +/- 6.7% versus 11.6 +/- 6.9%, P=.04), but zinc absorption was not (24.5 +/- 10.7% versus 22.8 +/- 7.6%, P=.2). In either case, however, a single daily serving provided most of the iron and zinc requirements for the children. CONCLUSIONS: Single daily servings of multinutrient-fortified beverages can meet much of the mineral needs for small children. Food has a small inhibitory effect on iron, but not zinc, absorption; therefore, these beverages can be efficacious even when given with a meal.

Anthropometry↗
PubMed2004

Metabolic adaptations to low zinc intakes in premenarcheal girls.

BACKGROUND: Zinc deficiency is increasingly recognized as an important cause of mortality and morbidity. Children in developing countries are at especially high risk because of relatively low zinc intakes and poor bioavailability. OBJECTIVE: We assessed the effect of 2-wk adaptation to low zinc intake (4 mg/d) on fractional zinc absorption, endogenous fecal zinc excretion, and urinary zinc excretion. DESIGN: Sixteen healthy 9-14-y-old girls were studied twice in random order after 2-wk adaptation to diets providing either 12 mg/d (high) or 4 mg/d (low) zinc. Fractional zinc absorption and endogenous fecal zinc excretion were measured with use of established stable isotope techniques. RESULTS: Plasma zinc was not significantly lower during the low dietary intake period (1.06 +/- 0.18 mg/L) than during the high dietary intake period (1.14 +/- 0.23 mg/L, P = 0.30). Endogenous fecal zinc excretion was significantly lower during the low intake period (1.08 +/- 0.62 mg/d) than during the high intake period (1.82 +/- 0.95 mg/d, P < 0.026), but there was no significant change in fractional zinc absorption (30.6% +/- 12.4% compared with 26.6% +/- 9.0%, P = 0.32) or urinary zinc excretion (0.68 +/- 0.35 mg/d compared with 0.59 +/- 0.24 mg/d, P = 0.30). Approximate zinc balance was significantly lower during the low-intake period than during the high-intake period (P = 0.007) and significantly (P < 0.0001) less than zero. CONCLUSION: Short-term zinc restriction in premenarcheal girls leads to a significant decrease in endogenous fecal zinc excretion, which was inadequate to restore normal zinc balance.

Adaptation, Physiological↗
PubMed2004

Calcium homeostasis during pregnancy and lactation in Brazilian women with low calcium intakes: a longitudinal study.

BACKGROUND: Physiologic adjustments in calcium homeostasis during pregnancy and lactation in women with marginal calcium intakes have not been described. OBJECTIVE: The objective was to examine longitudinal changes in various aspects of calcium homeostasis during pregnancy and lactation in 9 healthy Brazilian women who habitually consumed approximately 500 mg Ca/d. DESIGN: Calcium homeostasis was assessed at 3 time points: 10-12 (early pregnancy, EP) and 34-36 (late pregnancy, LP) wk of pregnancy and 7-8 wk postpartum (early lactation, EL). At each time point, the following variables were measured: dietary calcium intake with a 3-d weighed food record, 24-h urinary calcium excretion (UCa), intestinal calcium absorption (%CaAbs) via administration of stable calcium isotopes with a breakfast meal, serum 1,25-dihydroxyvitamin D, parathyroid hormone (PTH), insulin-like growth factor I (IGF-I), and biochemical markers of bone turnover. RESULTS: Dietary calcium did not change during the study. %CaAbs increased from 69.7 +/- 5.4% ( +/- SEM) during EP to 87.6 +/- 4.5% during LP (P < 0.05) and returned to 65.1 +/- 6.2% during EL. Compared with EP, UCa decreased 22% during LP and 68% during EL (P < 0.05). The net mean change in calcium retention was 212 mg/d during LP and 182 mg/d during EL. Several significant associations were found between the main outcome variables (%CaAbs, UCa, and markers of bone turnover) and serum hormones, especially IGF-I and PTH. CONCLUSIONS: Calcium homeostasis appears to be attained by a more efficient intestinal calcium absorption during pregnancy and by renal calcium conservation during both pregnancy and lactation. IGF-I and PTH seem to play major roles in the adjustment of calcium metabolism during pregnancy and lactation.

Adult↗
PubMed2004

Calcium absorption in Nigerian children with rickets.

BACKGROUND: Nutritional rickets is common in Nigerian children and responds to calcium supplementation. Low dietary calcium intakes are also common in Nigerian children with and without rickets. OBJECTIVE: The objective was to assess intestinal calcium absorption in Nigerian children with rickets. DESIGN: Calcium absorption was assessed in 15 children with active rickets (2-8 y of age) and in 15 age- and sex-matched children without rickets by using a dual-tracer stable-isotope method. The children with rickets were supplemented with calcium for 6 mo; calcium absorption was reevaluated 12 mo after the baseline study. Fractional calcium absorption could be determined in 10 children with rickets and in 10 children without rickets. RESULTS: The children with and without rickets had dietary calcium intakes of approximately 200 mg/d. Compared with the control children, the children with rickets had lower serum 25-hydroxyvitamin D and calcium concentrations and greater 1,25-dihydroxyvitamin D and parathyroid hormone concentrations. In fact, there were 15 rachitic and 15 control children in the study. Mean (+/-SD) fractional calcium absorption did not differ between those with (61 +/- 20%) and without (63 +/- 13%) rickets (P = 0.47). Calcium absorption was not associated with serum concentrations of calcium, alkaline phosphatase, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, or parathyroid hormone. Mean fractional calcium absorption was significantly greater after (81 +/- 10%) than before (61 +/- 20%) calcium supplementation for the treatment of rickets (P = 0.035). CONCLUSIONS: In Nigerian children with rickets, the capacity to absorb calcium is not impaired; however, fractional calcium absorption increases after the resolution of active disease. Calcium absorption may be inadequate to meet the skeletal demands of children with rickets during the active phase of the disease, despite being similar to that of control children.

Calcium↗
PubMed2004

Na2EDTA enhances the absorption of iron and zinc from fortified rice flour in Sri Lankan children.

Rice flour was proposed as a vehicle for iron and zinc fortification in Sri Lanka. Although widely consumed, rice flour has not been evaluated as a fortified food, and the absorption of minerals including iron and zinc from this flour is unknown. Determination of the bioavailability of these nutrients is a critical step before commencing a fortification program. We randomly divided 53 Sri Lankan schoolchildren ages 6-10 y into 4 groups that consumed a local dish prepared with 25 g of fortified rice flour labeled with one of the following: 1) (58)FeSO(4) 2) (58)FeSO(4) + Na(2)EDTA 3) (58)FeSO(4) + (67)ZnO or, 4) (58)FeSO(4) + Na(2)EDTA + (67)ZnO. The levels of iron and zinc were 60 mg/kg; the rice flour also contained folate at 2 mg/kg in each group. Na(2)EDTA was added at a Fe:Na(2)EDTA, 1:1 molar ratio. A total of 48 children completed the trial. Absorption of (58)Fe from a meal was significantly greater (P < 0.01) in the groups administered FeSO(4) + Na(2)EDTA (4.7 +/- 3.6%) than in those administered FeSO(4) without Na(2)EDTA (2.2 +/- 1.3%). Fractional absorption of zinc was 13.5 +/- 6.0% in the FeSO(4) + Na(2)EDTA group and 8.8 +/- 2.0% in the FeSO(4) group (P = 0.037). Although zinc absorption was low, our results demonstrated a benefit in using Na(2)EDTA to improve both iron and zinc absorption. We conclude that the fortification of rice flour is feasible, although additional strategies such as dephytinization or an increase in the level of iron and zinc fortification should be considered to obtain a higher proportion of the daily requirement of total absorbed iron and zinc.

Absorption↗
PubMed2004

The poor bioavailability of elemental iron in corn masa flour is not affected by disodium EDTA.

The most sustainable way to eradicate iron deficiency is through food fortification. Elemental iron powders are commonly utilized as fortificants due to their low cost and few sensory problems. However, their bioavailability is unknown. Our goals were to measure the bioavailability of elemental iron in Mexican style corn masa flour tortillas and to evaluate the effects of Na(2)EDTA. We used a stable isotope of H(2)-reduced iron powder, with and without Na(2)EDTA in tortillas prepared with corn masa flour. Two groups of 5- to 7-y-old children (n = 12/group) were fed tortillas to which was added 3 mg/100 g of H(2)-reduced (58)Fe with a mean particle size of 15 micro m. In one group, Na(2)EDTA was incorporated at a ratio of 1:2 mol/mol. The next day, (57)Fe ascorbate was given as a reference dose. After 14 d, blood samples were analyzed for isotopic enrichment. When normalized to 40% absorption of the reference dose, the geometric mean (+/-range 1 SD) bioavailability of reduced iron in tortilla was 3.8% (2.7-5.3). The addition of Na(2)EDTA, tended to increase it (P = 0.18) to 5.1% (2.8-9.2). This observed low absorption was compounded by the use of iron isotopes with smaller particle size (mean diameter 15 micro m) than typical of commercial elemental iron powder (<45 micro m). We conclude that H(2)-reduced iron powder is an ineffective fortificant in corn tortillas.

Biological Availability↗
PubMed2004

Kinetic parameters and plasma zinc concentration correlate well with net loss and gain of zinc from men.

The search for a reliable, convenient indicator of Zn status was the focus of research for several decades. Plasma Zn concentration is still the most widely used clinical measurement, despite the known problems of interpretation. More recently, researchers suggested that isotopically determined kinetic parameters, such as the exchangeable Zn pool (EZP), may more accurately and reliably reflect body Zn status. The objective of this study was to examine the relationship between net body Zn loss and gain during acute changes in dietary Zn intake with biochemical and kinetic indices of Zn status. Five men participated in an 85-d Zn depletion/repletion study. Net body Zn loss and gain were determined from the difference between dietary plus intravenously administered Zn and Zn excretion. Biochemical indicators of Zn status included plasma Zn, plasma alkaline phosphatase activity, and plasma retinol binding protein concentration. Following intravenous administration of (70)Zn or (67)Zn, a compartmental model was used to determine EZP mass, fractional Zn absorption, endogenous zinc excretion (EZE), and plasma Zn flux. The changes in total body zinc correlated best with changes in plasma Zn (r(2) = 0.826, P < 0.001), EZE (r(2) = 0.773, P < 0.001), and plasma Zn flux (r(2) = 0.766, P < 0.001). This study confirms that plasma Zn concentration is a valid indicator of whole-body Zn status in the absence of confounding factors; however, further research is needed to determine how kinetic parameters respond to conditions where plasma Zn concentration is known to be unreliable.

Absorption↗
PubMed2004

Safety and efficacy of human milk fortification for very-low-birthweight infants.

For full-term infants in the first 6 months of life, exclusive breastfeeding remains the nutritional standard for calcium intake. However, unsupplemented human milk does not meet the nutritional requirements for growth of the very-low-birthweight (<1500 g) infant. Methods for human milk fortification have been evaluated, and recent studies have demonstrated the safety of these fortifiers.

Calcium↗
PubMed2004

Improved estimation of the calcium content of total digestive secretions.

Because endogenous fecal calcium (EFC) excretion plays a larger role in the calcium economy of adults than does actual calcium intake, and because at typical absorption efficiencies EFC is largely determined by endogenous entry of calcium into the gut [total intestinal calcium (TIC)], it is important to be able to quantify TIC when studying the effect of nutrients, drugs, and disease on body calcium handling. Measured values for EFC, derived from 553 balance studies in middle-aged women (mean age, 48.8 yr), were pooled with 76 values obtained from premenarcheal girls (mean age, 11.2 yr) after adjusting for differences in body size. The aggregate sample provided values for calcium absorption efficiencies spanning a range from under 10% to over 90%. EFC is known to be inversely related to fractional calcium absorption (AbsFx), and the broad range of absorption efficiencies provided by the composite sample allowed derivation of reasonably precise estimates of EFC at 0% and 100% absorption. These were 0.8067 (+/- 0.0143) mg/cm height.d and 0.1799 (+/- 0.0310) mg/cm height.d, respectively. At 0% absorption, EFC is identical to the total entry of calcium into the intestine from endogenous sources (secretions plus sloughed mucosa), whereas at 100% absorption, EFC measures only endogenous entry effectively distal to the absorptive surface. The partition described facilitated derivation of a formula to calculate TIC for any paired values of EFC and AbsFx, i.e. TIC = EFC/[0.223 + 0.777 (1 - AbsFx)].

Bodily Secretions↗
PubMed2003

Effect of orange and apple juices on iron absorption in children.

OBJECTIVE: To measure iron absorption in children from meals containing apple juice or orange juice so as to determine if iron absorption will be greater with orange juice because of its higher ascorbic acid content than apple juice, a noncitrus fruit juice that US children reportedly prefer. DESIGN: On 2 successive days, children consumed identical meals that included apple juice on one day and orange juice on the other, in random order. The meals were labeled with iron-57 on one day and iron-58 on the other. Iron absorption was measured from red blood cell incorporation of the iron stable isotopes 14 days later. SETTING: Nutrition research institute in a major metropolitan medical center. PATIENTS: A total of 25 healthy children, 3 to 6 years of age, were recruited, of whom 21 (11 male and 10 female) completed the study. Intervention Identical meals served with orange juice and apple juice were given on consecutive days, in a balanced randomized design. MAIN OUTCOME MEASURES: Iron absorption measured by established stable isotope methods. RESULTS: Median iron absorption from the meal ingested with apple juice was 7.17% (mean +/- SD, 9.48% +/- 9.68%). Median iron absorption from the meal ingested with orange juice was 7.78% (9.80% +/- 6.66%; P =.44). Iron absorption from the meal that included apple juice was significantly correlated with serum ferritin concentration (P =.02); iron absorption from the meal that included orange juice tended to correlate with serum transferrin receptor concentration (P =.051). CONCLUSIONS: As children absorb iron well from a meal that includes either orange or apple juice, a preference for apple juice does not pose a concern with regard to the prospect of iron-deficiency anemia, which remains a significant health problem in the United States.

Anemia, Iron-Deficiency↗
PubMed2003

Maternal iron status influences iron transfer to the fetus during the third trimester of pregnancy.

BACKGROUND: The effect of maternal iron status on fetal iron deposition is uncertain. OBJECTIVE: We used a unique stable-isotope technique to assess iron transfer to the fetus in relation to maternal iron status. DESIGN: The study group comprised 41 Peruvian women. Of these women, 26 received daily prenatal supplements containing iron and folate (n = 11; Fe group) or iron, folate, and zinc (n = 15; Fe+Zn group) from week 10-24 of pregnancy to 1 mo postpartum. The remaining 15 women (control group) received iron supplementation only during the final month of pregnancy. During the third trimester of pregnancy (+/- SD: 32.9 +/- 1.4 wk gestation) oral 57Fe (10 mg) and intravenous 58Fe (0.6 mg) stable iron isotopes were administered to the women, and isotope enrichment and iron-status indicators were measured in cord blood at delivery. RESULTS: The net amount of 57Fe in the neonates' circulation (from maternal oral dosing) was significantly related to maternal iron absorption (P < 0.005) and inversely related to maternal iron status during the third trimester of pregnancy: serum ferritin (P < 0.0001), serum folate (P < 0.005), and serum transferrin receptors (P < 0.02). Significantly more 57Fe was transferred to the neonates in non-iron-supplemented women: 0.112 +/- 0.031 compared with 0.078 +/- 0.042 mg in the control group (n = 15) and the Fe and Fe+Zn groups (n = 24), respectively (P < 0.01). In contrast, 58Fe tracer in the neonates' circulation was not significantly related to maternal iron status. CONCLUSION: The transfer of dietary iron to the fetus is regulated in response to maternal iron status at the level of the gut.

Adolescent↗
PubMed2003

A multinutrient-fortified beverage enhances the nutritional status of children in Botswana.

Due to their widespread acceptability, multinutrient-fortified foods and beverages may be useful in reducing micronutrient deficiencies, especially in developing countries. We studied the efficacy of a new fortified beverage in improving the nutritional status of children in Botswana. We screened 311 lower income urban school children, ages 6-11 y, in two primary schools near Gaborone. Children were given seven 240-mL servings weekly of either an experimental beverage (EXP) fortified with 12 micronutrients or an isoenergetic placebo drink (CON) for 8 wk. Weight, mid-upper arm circumference, hemoglobin, retinol, ferritin, vitamin B-12, folate and riboflavin status were measured at baseline and at the end of the study. Plasma zinc and serum transferrin receptors also were measured at study end. A total of 145 children in the EXP group and 118 in the CON group completed the trial. Using multivariate analysis, the changes in mid-upper arm circumference, weight for age and total weight were significantly better in the EXP group than in the CON group (P < 0.01). Ferritin, riboflavin and folate status were significantly better in the EXP group than in the CON group at study end (P < 0.01), but serum vitamin B-12 was not. Zinc was significantly higher and transferrin receptors were significantly lower at the conclusion of the study in the EXP group than in the CON group (P < 0.001). Mean plasma retinol concentrations, which were low (<0.7 micro mol/L) in both groups, did not change. We conclude that a micronutrient-fortified beverage may be beneficial as part of a comprehensive nutritional supplementation program in populations at risk for micronutrient deficiencies.

Anthropometry↗
PubMed2003

Calcium, magnesium, phosphorus and vitamin D fortification of complementary foods.

Provision of the bone minerals and vitamin D as fortificants in food or as dietary supplements designed for older infants and toddlers in Latin America is likely to be beneficial and safe. Currently available data are inadequate to establish the precise amounts of these nutrients that would be required for such a supplement. These amounts would vary according to the local base diet. However, reasonable estimates can be made on the basis of current dietary recommendations as well as existing data on bioavailability and customary intake. The strongest case can be made for calcium and vitamin D supplementation. Because excessive dietary calcium can reduce zinc absorption as a result of interactive effects within the intestine, an appropriate ratio of calcium to zinc should be used, even if this means adding zinc as a fortificant or supplement. Magnesium supplementation may be appropriate in some circumstances but it cannot be routinely advocated at present. It is unlikely that phosphorus supplementation is needed for most population groups because of the relatively high usual dietary phosphorus intakes, primarily from phosphate salts added to carbonated beverages and as food preservatives.

Calcium↗
PubMed2003

Normal acquisition and loss of bone mass.

The natural patterns of bone mass accumulation and loss with age represent the templates of individual life cycle periods that are distinguished by marked, physiologically and genetically identifiable, changes in bone mass. During the third trimester of pregnancy, maternal calcium absorption increases and the fetus accumulates about two-thirds of the total bone mass of the term infant. In early infancy, human milk calcium is derived primarily from maternal bone stores, which incur substantial bone losses that are quickly replenished during and after weaning. At puberty, a marked increase in bone mass occurs in conjunction with the initial physical and hormonal changes that characterize this stage. Calcium absorption and bone calcium deposition rates peak in females shortly before menarche. At that time, the bone calcium deposition rate is approximately five times that of adulthood. Skeletal bone mass reaches over 90% of its maximum by age 18 (earlier in females) but does not peak until age 25-30. At some point in mid-life, women experience perimenopause, the 3- to 5-year period prior to menopause during which estrogen levels begin to drop and there are marked increases in bone resorption and loss. Throughout adulthood, calcium absorption efficiency from the diet gradually declines.

Adolescent↗
PubMed2003

Inductively coupled plasma mass spectrometric analysis of calcium isotopes in human serum: a low-sample-volume acid-equilibration method.

BACKGROUND: Analytical methods for measuring the calcium isotope distribution in enriched human serum samples that use low blood volumes, simple preparation methods, and rapid analysis are important in clinical studies of calcium kinetics. Previously, sample preparation by oxalate precipitation typically required 500 micro L of serum. This method was time-consuming, and the blood volume required was limiting in circumstances when only a small amount of serum could be obtained. METHODS: Serum was collected from humans who were administered (42)Ca, and 20 micro L of serum was mixed with 2 mL of 0.22-0.67 mol/L HNO(3) at room temperature for between 1 min and 16 h. The (42)Ca/(43)Ca ratio in the supernatant was measured by a magnetic sector inductively coupled plasma mass spectrometer (ICP-MS). Calcium isotope ratios from these equilibration solutions were compared with data from oxalate-precipitated serum samples to determine the optimum equilibrium time and the effect of acid concentration on equilibrium. RESULTS: Various amounts of aggregated particles developed in different acid-serum mixtures. These affected the time required for isotope equilibration in the mixture. The shortest equilibrium time needed for the calcium isotopes varied from 1 to 6 h for samples acidified with 0.22-0.45 mol/L HNO(3). Data obtained from these solutions were consistent with data from oxalate-precipitated calcium. The precision of (42)Ca/(43)Ca ratio measurements was better than 0.5%. CONCLUSIONS: We have developed a simple, rapid sample preparation technique for ICP-MS analysis in which 20 micro L of serum can be used for accurate measurement of the calcium isotope distribution in a sample with good precision and a rapid analysis time.

Calcium↗