Building Bones in Babies: Can and Should We Exceed the Human Milk-Fed Infant's Rate of Bone Calcium Accretion?

Increasing calcium absorption and bone calcium accretion to levels above those achieved by human milk-fed, full-term infants is possible with infant formulas. However, no data support such a goal or suggest that it is beneficial to short- or long-term bone health. Small differences in the bioavailability of calcium between infant formulas are unlikely to have long-term consequences. Long-term studies of the effects of infant feeding type on ultimate bone mass are needed. For now, the vitamin-replete breast-fed infant's rate of calcium accretion during the first year of life should be the standard targeted for infant formulas.

Iron deficiency, but not anemia, upregulates iron absorption in breast-fed peruvian infants

Iron absorption in adults is regulated by homeostatic mechanisms that decrease absorption when iron status is high. There are few data, however, regarding the existence of a similar homeostatic regulation in infants. We studied 2 groups of human milk-fed infants using (57)Fe (given as ferrous sulfate without any milk) and (58)Fe (given at the time of a breast-milk feeding) stable isotopes to determine whether healthy infants at risk for iron deficiency would regulate their iron absorption based on their iron status. We studied 20 Peruvian infants at 5-6 mo of age and 18 infants at 9-10 mo of age. We found no effect of infant hemoglobin concentration on iron absorption with 5-6 mo-old infants absorbing 19.2 +/- 2.1% and 9- to 10-mo-old infants absorbing 25.8 +/- 2.6% of the (57)Fe dose. For (58)Fe, 5- to 6-mo-old infants absorbed 42.6 +/- 5.0% and 9 to 10-mo-old infants absorbed 51.9 +/- 10.3%. Following log transformation, iron absorption from (57)Fe (r = -0.61, P = < 0.001) and (58)Fe (r = -0.61, P = < 0.001) were inversely correlated to serum ferritin (S-Ft). For both the (57)Fe and (58)Fe doses, infants with S-Ft <12 mg/L (n = 11) had significantly higher iron absorption than those with S-Ft >12 mg/L. We concluded that iron absorption in infants is related to iron status as assessed by serum ferritin but not hemoglobin concentration. Infants with low iron status upregulate iron absorption from breast milk at both 5-6 and 9-10 mo of age.

Effect of beef and soy proteins on the absorption of non-heme iron and inorganic zinc in children

BACKGROUND

Iron and zinc deficiency remain substantial problems in small children in both developed and developing nations. Optimizing mineral absorption is an important strategy in minimizing this problem.

OBJECTIVES

To assess the effects of beef and soy proteins on the bioavailability of non-heme iron and zinc in children.

METHODS

We measured iron (n = 26) and zinc (n = 36) absorption in 4-8 y old children from meals differing only in protein source (beef or a low-phytate soy protein concentrate). Iron and zinc absorption were measured using multi-tracer stable isotope techniques. Iron absorption was calculated from the red blood cell iron incorporation measured after 14 days and zinc absorption from the ratio of the oral and intravenous excretion of the zinc tracers 48 hours after dosing.

RESULTS

Iron absorption from the beef meal was significantly greater (geometric mean, 7.6%) than from the soy meal (3.5%, p = 0.0015). Zinc absorption from the beef meal was greater (mean +/- SD, 13.7 +/- 6.0%) than from the soy meal (10.1 +/- 4.1%, p = 0.047).

CONCLUSION

These findings indicate that beef protein increases both non-heme iron and zinc absorption compared to soy protein. The effect of protein source on non-heme iron and inorganic zinc absorption should be one of the factors taken into account when designing diets for children. The inhibitory effect of the soy based meal on iron and zinc absorption could be overcome by fortifying the soy protein with these minerals during the production process.

An Educational Program Enhances Food Label Understanding of Young Adolescents

While much research has focused on intake and eating behaviors of young adolescents, few studies have examined their knowledge of the Nutrition Facts label. The goals of this project were to assess the understanding of Nutrition Facts labels and the response of young adolescents to an educational program about Nutrition Facts labels. Thirty-four young adolescents participated by answering a short questionnaire and taking a pretest about Nutrition Facts labels and their food choices, which involved using actual Nutrition Facts labels from foods typically eaten by adolescents. Then the subjects participated in a short educational program on how to read the Nutrition Facts label. This was followed by a posttest. Initial knowledge of the basic use of the Nutrition Facts label was marginal, with only 6.65 (standard deviation=2.23) or approximately 55% of pretest questions answered correctly. However, the subjects' scores improved significantly to 8.32 (standard deviation=2.01) or approximately 70% correct on the posttest (P<0.0001, Fisher's exact test) after the educational session. In conclusion, young adolescents can learn how to read and understand the Nutrition Facts labels through educational sessions.

Bone calcium turnover during pregnancy and lactation in women with low calcium diets is associated with calcium intake and circulating insulin-like growth factor 1 concentrations

BACKGROUND

Few data exist on longitudinal changes in bone calcium turnover rates across pregnancy and lactation.

OBJECTIVE

Our aim was to characterize calcium kinetic variables and predictors of these changes across pregnancy and early lactation in women with low calcium intakes.

DESIGN

Stable calcium isotopes were administered to 10 Brazilian women during early pregnancy (EP; weeks 10-12 of gestation), late pregnancy (LP; weeks 34-36 of gestation), and early lactation (EL; 7-8 wk postpartum). Multicompartmental modeling was used to assess the rates of bone calcium turnover in relation to calcium intakes and circulating concentrations of parathyroid hormone (PTH), insulin-like growth factor 1, and 1,25-dihydroxyvitamin D.

RESULTS

Rates of bone calcium deposition increased significantly from EP to LP (P = 0.001) and were significantly associated with serum PTH during LP (P < or = 0.01). Rates of bone calcium resorption were also higher during LP and EL than during EP (P < or = 0.01) and were associated with both PTH (P < or = 0.01) and IGF-1 (P < or = 0.05) during LP but not during EL. Net balance in bone calcium turnover was positively associated with dietary calcium during EP (P < or = 0.01), LP (P < or = 0.01), and EL (P < or = 0.01). The mean (+/-SD) calcium intake was 463 +/- 182 mg/d and, in combination with insulin-like growth factor 1, explained 68-94% of the variability in net bone calcium balance during pregnancy and lactation.

CONCLUSIONS

Net deficits in bone calcium balance occurred during pregnancy and lactation. Increased dietary calcium intake was associated with improved calcium balance; therefore, greater calcium intakes may minimize bone loss across pregnancy and lactation in women with habitual intakes of <500 mg calcium/d.

Relationships among vitamin D levels, parathyroid hormone, and calcium absorption in young adolescents

BACKGROUND

Evidence suggests that vitamin D status in adults, as assessed by serum 25-hydroxyvitamin D (25-OHD), is positively associated with calcium absorption fraction and inversely associated with serum PTH. Few comparable pediatric data exist.

OBJECTIVES

The objective of this study was to evaluate the relationships among vitamin D status, PTH, and calcium absorption in midpubertal boys and girls.

METHODS

Calcium absorption was measured as part of an evaluation of the effects of prebiotics (inulin-type fructans) using a stable isotope method in 93 young adolescents, 12.7 +/- 1.0 yr of age, receiving diets averaging approximately 900 mg/d calcium.

RESULTS

A significant positive relation to calcium absorption was found for serum 1,25-dihydroxyvitamin D (P = 0.048) and PTH (P = 0.007), but not for 25-OHD (P = 0.77). PTH was significantly inversely related to 25-OHD and was positively related to serum 1,25-dihydroxyvitamin D and osteocalcin. PTH was marginally significantly inversely related to lumbar spinal, but not whole body, bone mineral density.

CONCLUSIONS

These data suggest that in adolescents, especially in the presence of vitamin D insufficiency, PTH secretion increases to adapt to higher rates of bone formation associated with growth. This results in higher serum 1,25(OH)2D concentrations and increased calcium absorption results. Vitamin D status, as reflected by the serum 25-OHD level, is not closely related to calcium absorption. Whether adaptation to low serum 25-OHD is adequate under physiologically stressful situations, including those leading to very low serum 25-OHD levels, is unknown.

Height and height Z-score are related to calcium absorption in five- to fifteen-year-old girls

CONTEXT

Understanding the relationship between calcium absorption and growth has been limited. We have developed a database of calcium absorption measurements in 315 girls aged 5.0-15.0 yr.

DESIGN

We have used this database to assess the relationship between height, its age- and gender-normalized value (height Z-score), and calcium absorptive efficiency.

RESULTS

Overall, height was significantly related to calcium absorption (corrected for calcium intake, age, Tanner, stage, and ethnicity) (P = 0.001). Similarly, height Z-score was significantly related to calcium absorption (P < 0.007). About 3-3.5% of the variability (eta2) of absorption was associated with height or height Z-score. We found that calcium absorption was significantly lower in girls with height Z-score equal to or less than zero compared with those with a height Z-score more than zero (difference, 3.9 +/- 1.4%, mean +/- sem; P = 0.007). Limiting the analysis to those girls in which Tanner staging was performed or those age 9 yr or older did not substantively affect these relationships.

CONCLUSION

These results indicate that a small but significant component of the variability in calcium absorption is due to height. Identifying genetic risk factors for lowered calcium absorption during growth could lead to individual approaches for prevention of inadequate bone mass.

Methodological considerations in measuring human calcium absorption: relevance to study the effects of inulin-type fructans

During the last 50 years, a variety of methods have been developed to estimate Ca absorption in man. Mass balances were initially used, but these were unable to accurately measure fractional Ca absorption because they cannot distinguish unabsorbed dietary Ca from endogenous faecal Ca excretion (excretion of previously absorbed Ca back into the gut). A number of isotopic methods have been developed that can measure true fractional Ca absorption, employing radioisotopes, stable isotopes, or both. Different methods involve collection of urine, faecal or plasma samples. Of the currently available methods, the dual isotope tracer method with a timed urine collection is probably the most precise and reliable. It is also relatively straightforward to carry out and avoids the need for a faecal collection. The purpose of the present paper is to discuss the general advantages and disadvantages of the different methods of Ca absorption. In addition, the limitations the different methods have in examining the possible effects of non-digestible oligosaccharides on Ca absorption will be discussed.

A combination of prebiotic short- and long-chain inulin-type fructans enhances calcium absorption and bone mineralization in young adolescents

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.

High resolution inductively coupled plasma mass spectrometry allows rapid assessment of iron absorption in infants and children

Stable isotope absorption studies of iron have been limited by the high cost and limited availability of isotope ratio analysis using thermal ionization MS (TIMS). The development of high-resolution double focusing inductively coupled plasma MS (ICP-MS) may permit more cost-efficient sample analysis due to its high throughput, lower cost, easy sample pretreatment, and greater availability. Our objective was to develop an ICP-MS methodology for the measurement of iron isotope ratios using very small blood volumes. We developed a technique using multiple iron-nickel mixing standard solutions to adjust for nickel interference calibration. RBC samples from human subjects previously given 58Fe and 57Fe were analyzed for iron isotope ratios and compared with our current methodology (TIMS). Reproducibility of iron isotope ratios provided external relative SD < 0.5 and 0.7% (1 SD) for 57Fe/54Fe and 58Fe/54Fe, respectively. Iron isotope ratios from ICP-MS analysis did not differ from those from TIMS based on statistical analyses, nor did the calculated iron absorption values. The mean and SD of iron absorption did not differ when measured by TIMS or ICP-MS. A 2-microL RBC sample was sufficient for ICP-MS iron isotope ratio analysis with an internal relative SD < 0.5% and analytical time < 5 min. This technique may assist groups in increasing their use of stable isotope methods to assess iron absorption in infants and children.

Calcium Supplementation during Childhood: Long-term Effects on Bone Mineralization

Calcium supplementation has been shown to increase bone mineralization in children and adolescents. However, catch-up mineralization later in puberty appears likely if intake is consistent with usual average intakes in the United States. Ultimately, individualized risk assessment will be developed based on genetic and lifestyle factors that can be used to guide optimal calcium intake during childhood.

Effects of potassium alkali and calcium supplementation on bone turnover in postmenopausal women

Potassium citrate may improve calcium balance by conferring an alkali load. Calcium supplementation slows postmenopausal bone loss by inhibiting PTH secretion. This study explores whether combined treatment with potassium citrate and calcium citrate is more effective than either agent alone in inhibiting bone loss. In a crossover study involving 18 postmenopausal women, the following treatments were compared: potassium citrate (4.3 g or 40 mmol/d), calcium citrate (800 mg or 20 mmol/d), combined treatment, and placebo. During the last 2 d of each 2-wk phase, serum and 24-h urine were collected for assessment of calcium metabolism, alkali load, and bone turnover markers. Compared with placebo, potassium citrate provided an alkali load and significantly decreased urinary calcium without changing serum PTH (sPTH) or bone turnover markers. Calcium citrate significantly increased absorbed calcium, marginally decreased sPTH, and significantly reduced bone resorption markers. Combined treatment retained key features of potassium citrate and calcium citrate. However, more alkali was delivered than with potassium citrate alone, and absorbed calcium did not differ from calcium citrate alone. Compared with placebo, combined treatment increased urinary calcium, marginally reduced sPTH, provided a clear alkali load, and reduced the bone resorption markers serum type I collagen C-telopeptide and urinary N-telopeptide by 20.4% (P < 0.0001) and 18.2% (P = 0.005), respectively. A significant trend was noted for the decrease in bone resorption markers as treatment changed from placebo to potassium citrate to calcium citrate to combined treatment. In postmenopausal women, combined treatment with potassium citrate and calcium citrate inhibits bone resorption by providing an alkali load and increasing absorbed calcium.

Vitamin D receptor Fok1 polymorphisms affect calcium absorption, kinetics, and bone mineralization rates during puberty

Few studies of the VDR polymorphisms have looked at calcium metabolism or long-term effects. We measured bone mineralization and calcium metabolic parameters longitudinally in a group of 99 adolescents. We found a significant relationship between calcium absorption and skeletal calcium accretion and the Fok1, but not other VDR or related, genetic polymorphisms. It seems that the Fok1 polymorphism directly affects bone mineralization during pubertal growth through an effect on calcium absorption.

INTRODUCTION

There are few data regarding the relationship between genetic markers for low bone mass and changes in calcium metabolism in childhood or adolescence. We sought to identify the effects of polymorphisms of the vitamin D receptor (VDR) on calcium and bone mineral metabolism in a longitudinal study of pubertal adolescents.

MATERIALS AND METHODS

Adolescents (n = 99) received comprehensive stable isotope studies of calcium absorption, bone calcium kinetics, and bone mineralization. Studies were repeated 12 months later. Polymorphisms of putative genetic markers were determined and related to bone mineralization and calcium metabolic finding. Results were analyzed by ANOVA in which changes over time were determined using the initial value as a covariate.

RESULTS

Polymorphisms of the Fok1 gene of the VDR were significantly related to calcium absorption (p = 0.008) and whole body BMC (p = 0.03) and BMD (p = 0.006). The Fok1 effect on whole body BMD was significant for those with Ca intake >800 mg/day (p < 0.001), whereas for those with Ca intake < or = 800 mg/day, the Fok1 genotype did not have a significant effect on whole body BMD (p = 0.40). The Fok1 genotype was significantly related to the changes during the year in whole body calcium accretion, with the ff genotype having a 63 +/- 20 mg/day deficit compared with the FF genotype (p = 0.008).

CONCLUSIONS

The Fok1 polymorphism of the VDR receptor seems to directly affect bone mineral accretion during pubertal growth through an effect on calcium absorption. The relationship between different genetic polymorphisms and bone mineral metabolism may vary by life stage as well as diet.

The addition of milk or yogurt to a plant-based diet increases zinc bioavailability but does not affect iron bioavailability in women

The addition of milk and milk-based products to the diets of individuals subsisting on plant-based diets was reported to have positive effects on nutritional status and functional outcomes such as growth, morbidity, and cognition. We examined the effect of the addition of milk or yogurt on the bioavailability of zinc and iron from a plant-based rural diet. The subjects were 48 Mexican women (30.9 +/- 5.7 y) who habitually consumed a plant-based diet. The women were assigned to 1 of 3 groups: 1) the typical rural Mexican diet, 2) that diet with milk added, or 3) that diet with yogurt for 13 d. Zinc absorption was measured after extrinsically labeling meals with (67)Zn and an i.v. dose of (70)Zn; iron absorption was measured by extrinsically labeling meals with (58)Fe and a reference oral dose of (57)Fe. Including milk and yogurt in the diet increased zinc absorption by 50 and 68%, respectively (P < 0.05). The 3 groups did not differ in the percentage iron absorption. The total amount of zinc absorbed was increased (P < 0.05) by 70% when milk was added to the meal and 78% when yogurt was added. The total amount of iron absorbed did not differ among the groups. The addition of milk and yogurt to a plant-based diet high in phytate increases zinc bioavailability without affecting iron bioavailability.

Bone markers, calcium metabolism, and calcium kinetics during extended-duration space flight on the mir space station

Bone loss is a current limitation for long-term space exploration. Bone markers, calcitropic hormones, and calcium kinetics of crew members on space missions of 4-6 months were evaluated. Spaceflight-induced bone loss was associated with increased bone resorption and decreased calcium absorption.

INTRODUCTION

Bone loss is a significant concern for the health of astronauts on long-duration missions. Defining the time course and mechanism of these changes will aid in developing means to counteract these losses during space flight and will have relevance for other clinical situations that impair weight-bearing activity.

MATERIALS AND METHODS

We report here results from two studies conducted during the Shuttle-Mir Science Program. Study 1 was an evaluation of bone and calcium biochemical markers of 13 subjects before and after long-duration (4-6 months) space missions. In study 2, stable calcium isotopes were used to evaluate calcium metabolism in six subjects before, during, and after flight. Relationships between measures of bone turnover, biochemical markers, and calcium kinetics were examined.

RESULTS

Pre- and postflight study results confirmed that, after landing, bone resorption was increased, as indicated by increases in urinary calcium (p < 0.05) and collagen cross-links (N-telopeptide, pyridinoline, and deoxypyridinoline were all increased >55% above preflight levels, p < 0.001). Parathyroid hormone and vitamin D metabolites were unchanged at landing. Biochemical markers of bone formation were unchanged at landing, but 2-3 weeks later, both bone-specific alkaline phosphatase and osteocalcin were significantly (p < 0.01) increased above preflight levels. In studies conducted during flight, bone resorption markers were also significantly higher than before flight. The calcium kinetic data also validated that bone resorption was increased during flight compared with preflight values (668 +/- 130 versus 427 +/- 153 mg/day; p < 0.001) and clearly documented that true intestinal calcium absorption was significantly lower during flight compared with preflight values (233 +/- 87 versus 460 +/- 47 mg/day; p < 0.01). Weightlessness had a detrimental effect on the balance in bone turnover such that the daily difference in calcium retention during flight compared with preflight values approached 300 mg/day (-234 +/- 102 versus 63 +/- 75 mg/day; p < 0.01).

CONCLUSIONS

These bone marker and calcium kinetic studies indicated that the bone loss that occurs during space flight is a consequence of increased bone resorption and decreased intestinal calcium absorption.

Ferrous sulfate is more bioavailable among preschoolers than other forms of iron in a milk-based weaning food distributed by PROGRESA, a national program in Mexico

After 1 y of distributing a milk-based fortified weaning food provided by the Mexican social program PROGRESA, positive effects on physical growth, prevalence of anemia, and several vitamin deficiencies were observed. There was no effect on iron status, which we hypothesized was related to the poor bioavailability of the reduced iron used as a fortificant in PROGRESA. The objective of this study was to compare the iron bioavailability from different iron sources added as fortificants to the weaning food. Children (n = 54) aged 2-4 y were randomly assigned to receive 44 g of the weaning food fortified with ferrous sulfate, ferrous fumarate, or reduced iron + Na(2)EDTA. Iron absorption was measured using an established double-tracer isotopic methodology. Iron absorption from ferrous sulfate (7.9 +/- 9.8%) was greater than from either ferrous fumarate (2.43 +/- 2.3%) or reduced iron + Na(2)EDTA (1.4 +/- 1.3%) (P < 0.01). The absorption of log-(58)Fe sulfate given with the iron source correlated with serum ferritin (s-ferritin) concentration (n = 13, r = 0.63, P = 0.01) and log-(57)Fe absorption (reference dose) (n = 14, r = -0.52, P = 0.02). Absorption from ferrous fumarate and reduced iron + Na2EDTA did not correlate with s-ferritin or absorption of (57)Fe. The recommended daily portion of the fortified complementary food provides an average of 0.256, 0.096, 0.046 mmol (1.44, 0.54, and 0.26 mg) of absorbed iron, if fortified with sulfate, fumarate and reduced iron + Na(2)EDTA, respectively. Ferrous sulfate was more bioavailable than either ferrous fumarate or reduced iron + Na(2)EDTA when added to the milk-based fortified food and more readily met the average daily iron requirements for children 2-3 y of age.

Safety and Efficacy of Human Milk Fortification for Very-Low-Birth-Weight 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.

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.

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.

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.

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.

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.

Current issues in nutritional management of very low birth weight infants

Infants less than 1,500 g birth weight (very low birth weight, VLBW) are at risk for significant nutritional deficiencies. Enhancing nutritional care of these infants during their first months of life may have important short and long-term benefits. In this article we will consider several areas of recent research in the nutritional management of VLBW infants. In particular we will focus on issues related to the introduction and use of enteral nutrition. These issues include avoiding mineral deficiencies, early (minimal) enteral nutrition, human milk fortification, and postdischarge nutrition. Transitioning VLBW infants successfully to enteral nutrition is a key to their achieving adequate growth and development without the long-term risks related to parenteral nutrition. Human milk is a key component of any strategy for enteral nutrition of all infants. Its introduction in the first days of life leads to improved growth and better health outcomes for infants. However, although some nutrients are initially increased in the milk of mothers delivering prematurely, there are inadequate amounts of calcium, phosphorus, zinc and other nutrients to meet the needs of the VLBW infant during growth. Therefore, safe and effective means of fortifying human milk are essential to the care of VLBW infants. The optimal approaches for this fortification and the potential risks related to human milk fortification remain controversial. Limited data are available for the optimal content, initiation and methods for mixing fortifier with human milk.

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.

Zinc metabolism in adolescents with Crohn's disease

Low serum zinc concentrations have been reported in Crohn's disease (CD) and overt zinc deficiency has been described, but little is known about the effect of CD on zinc metabolism in adolescents. The aim of this study was to measure zinc absorption, endogenous fecal zinc excretion, urinary zinc excretion, and zinc balance in children with stable CD and in matched controls. Subjects were 15 children, ages 8-18 y, with stable CD, and 15 healthy matched controls. Subjects were adapted to diets providing 12 mg/d elemental zinc for 2 wk, and then admitted for a 6-d metabolic study. Stable zinc isotopes were given intravenously and orally, and urine and feces collected for 6 d. Fractional zinc absorption, endogenous fecal zinc excretion, and zinc balance were calculated using established stable isotope methods. In subjects with CD, zinc absorption (10.9% +/- 6.1 versus 23.4 +/- 15.8, p = 0.008) and plasma zinc concentration (0.85 mg/dL +/- 0.15 versus 1.25 +/- 0.35, p = 0.004) were significantly reduced, compared with controls. Despite this, there were no significant differences in endogenous fecal zinc excretion (2.0 mg +/- 1.5 versus 1.5 +/- 1.5, p = 0.34) or urinary zinc excretion (0.9 mg +/- 0.7 versus 1.0 +/- 0.7, p = 0.47). Zinc balance was significantly lower in CD (-1.5 mg +/- 1.5) than in controls (+0.6 mg +/- 3.1, p < 0.0001). In conclusion, adolescents with CD have significantly reduced zinc absorption. Despite this, they were unable to reduce endogenous fecal zinc excretion to restore normal zinc balance and had a significantly worse zinc balance and lower plasma zinc concentration than controls.

CALCIUM AND BONE MINERAL METABOLISM IN CHILDREN WITH CHRONIC ILLNESSES

Increased longevity and improved medical management of children with chronic illnesses has led to a focus on the short- and long-term consequences of these conditions on bone health. Bone loss is influenced by diet, malabsorption, and disease-related imbalances in bone turnover. It may be exacerbated by common medications, especially corticosteroids. Assessment of bone mass and quality, calcium absorption, kinetically derived rates of bone turnover, and biochemical markers of bone turnover have increased our knowledge of the pathophysiology of bone loss in these children as well as provided insights into possible therapeutic interventions. Increased intake of calcium and vitamin D, while useful, is unlikely to prevent or resolve bone loss in many chronically ill children. Emphasis on combination of nutritional interventions with exercise and newer bone-sparing therapies may be necessary.

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.

Pubertal girls only partially adapt to low dietary calcium intakes

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.

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)].

Bioavailability of elemental iron powder in white wheat bread

OBJECTIVE

Iron fortification of wheat flour is widely used. In most cases, elemental iron powders are utilized as fortificants due to their lower cost and few, if any, sensory problems. However, their bioavailability is unknown. We aimed to measure the bioavailability of H(2)-reduced elemental iron powder in white wheat bread made from 72% extraction flour.

DESIGN

A stable isotope of H(2)-reduced iron powder (mean particle size 15 microm) was used as fortificant in bread prepared from unfortified wheat flour. In all, 12 5- to 7-y-old children were fed bread with 4 mg of H(2)-reduced (58)Fe /100 g of flour. The next day (57)Fe ascorbate was given as reference dose. After 14 days, erythrocytes were analyzed for isotopic enrichment using mass spectrometry.

RESULTS

When normalized to 40% absorption of the reference dose, the geometric mean (+/-range of 1 s.d.) bioavailability of reduced (58)Fe in wheat bread rolls was 6.5% (3.7-11.8).

CONCLUSIONS

When compared to previous radioiron studies of ferrous sulfate showing 10% absorption from an identical meal in adult women, the relative bioavailability can be estimated at about 65%. However, the bioavailability of this smaller particle size (58)Fe (15 microm) is likely to be higher than that of commercial iron powder (45 microm) although the precise difference cannot be ascertained with current methods. Thus, the bioavailability of commercial elemental iron powders currently used in fortification programs is likely to be substantially lower than that of ferrous sulfate.

SPONSORSHIP

This work was funded in part by Grant No 910313 by Micronutrient Initiative, IDRC, Ottawa, Canada.

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.

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 μL 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 42Ca, and 20 μL of serum was mixed with 2 mL of 0.22–0.67 mol/L HNO3 at room temperature for between 1 min and 16 h. The 42Ca/43Ca 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 HNO3. Data obtained from these solutions were consistent with data from oxalate-precipitated calcium. The precision of 42Ca/43Ca ratio measurements was better than 0.5%.

Conclusions: We have developed a simple, rapid sample preparation technique for ICP-MS analysis in which 20 μL of serum can be used for accurate measurement of the calcium isotope distribution in a sample with good precision and a rapid analysis time.

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.

Bone mineral mass in overweight and obese children: diminished or enhanced?

Childhood obesity has become a worldwide health problem. Recent studies have suggested that obese and overweight children have lower bone mass. We used dual-energy X-ray absorptiometry to examine the relation between bone mineral content (BMC) and body fatness (%Fat) in healthy children. Obese children (%Fat>30%) had higher BMC compared with age-, gender-, and ethnic-matched children with normal adiposity (%Fat<25%). When adjusted for height, these differences were less significant. We conclude obese children do not have lower whole-body BMC when compared with leaner children, even when adjusted for height, age, gender, and ethnicity.

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.

Zinc absorption by infants

Zinc is a vital mineral in human nutrition and rare cases of overt zinc deficiency are well described in term and preterm infants. A variety of methods have been developed to assess zinc absorption, retention and balance in humans, either using mass (metabolic) balance or stable isotope-based

METHODS

The different methods have different benefits and disadvantageous. Many studies have used such methods to examine zinc absorption in term and preterm infants. In preterm infants the main interest has been establishing whether different diets lead to positive zinc balance and approached in utero accretion rates. The earliest studies were concerning as they suggested that preterm infants may be in negative zinc balances for prolonged periods after birth. Subsequent studies have been more contradictory and it remains unclear from the literature how much zinc preterm infants absorb early in life. Nor is it clear whether poor zinc absorption during this period has any long-term consequences. Studies in term infants have suggested no such prolonged period of negative zinc balance. Generally the absorption values are in line with those used by the Institute of Medicine in the most recent edition of the Dietary Reference Intakes. Other studies have been designed to assess the effect of changes in formula composition on zinc intake (e.g. the presence or absence of lactose, high vs low zinc contents, etc.). Ho-wever, despite almost 20 studies of zinc absorption in infants many physiologically important questions remain unanswered, especially in preterm infants.

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.

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.

Using stable isotopes to assess the bioavailability of minerals in food-fortification programs

Food fortification with minerals is often undertaken without consideration of the bioavailability or nutrient-nutrient interactions related to its use. Stable isotopes provide a safe and accessible approach to providing direct evidence regarding these issues. Studies can be applied in all areas of the world and in all population groups. Mineral stable isotopes are safe and meet stringent ethical standards for use in children. Clinical studies in children allowing scientists, policy makers and the food industry to obtain data needed to understand how best to fortify foods to enhance the nutritional health of children of all ages. It is not necessary to have analytical mass spectrometry equipment available in each country where studies are performed. Rather, international collaborations can be developed to allow clinical studies to be performed in the field setting with analysis elsewhere if needed. The combination of isotope studies with field intervention trials may be beneficial.

Cofortification of iron-fortified flour with zinc sulfate, but not zinc oxide, decreases iron absorption in Indonesian children

BACKGROUND

Iron deficiency is a major nutritional concern in developing countries, and food fortification is a common strategy to treat it. In Indonesia wheat flour is fortified with 60 mg Fe/kg, but because of increasing concerns about marginal zinc status in at-risk populations, consideration is being given to cofortifying flour with zinc. However, little is known about the effect of zinc fortification of flour on iron bioavailability or about the optimum form of zinc supplementation.

OBJECTIVE

We measured iron and zinc bioavailability from wheat-flour dumplings containing 25 g flour fortified with 60 mg Fe/kg, either alone or with 60 mg Zn/kg as zinc oxide or as zinc sulfate.

DESIGN

Ninety children aged 4-8 y were recruited and assigned randomly to the 3 groups; 86 completed the study. Iron and zinc absorption were measured with established stable-isotope methods.

RESULTS

Iron absorption from the flour fortified with iron only was good (15.9 +/- 6.8%), but when corrections were made for hemoglobin concentrations, it was significantly lower from the flour cofortified with zinc sulfate (11.5 +/- 4.9%; P < 0.05) but not from the flour cofortified with zinc oxide (14.0 +/- 8.9%). Zinc absorption was not significantly different between the zinc oxide and zinc sulfate cofortified flours (24.1 +/- 8.2% compared with 23.7 +/- 11.2%; P = 0.87).

CONCLUSIONS

Iron and zinc appear to be highly bioavailable from foods made from fortified flour, but zinc sulfate cofortification may have a detrimental effect on iron absorption.

Using stable isotopes to assess the bioavailability of minerals in food fortification programs

The fortification of various types of food with minerals is often undertaken without consideration of either their bioavailability or the potential nutrient-nutrient interactions resulting from their use. Stable isotopes provide a safe and accessible method of resolving these issues by providing the proper evidence in each case. They must be conducted according to strict safety and ethical guidelines and may be readily conducted in a field setting. Clinical studies in children enable researchers, policymakers, and food manufacturers to obtain the data necessary to determine the best way to fortify specific foods and beverages, in order to optimally enhance the nutritional health of growing children. We have shown the utility of this approach in studies in both developing countries and in the United States.

Calcium and zinc absorption from lactose-containing and lactose-free infant formulas

BACKGROUND

Calcium absorption is enhanced by the presence of lactose, but the quantitative significance of this effect in infant formulas is uncertain. It is also not known whether lactose affects zinc absorption.

OBJECTIVE

We measured the absorption of calcium and zinc from infant formulas by using a multitracer, stable-isotope technique.

DESIGN

Eighteen full-term infants (aged 8-12 wk at enrollment) were fed 2 partially hydrolyzed whey-protein-based formulas ad libitum for 2 wk per formula. The carbohydrate source was lactose in one formula and glucose polymers in the other (lactose-free). Infants were studied in a blinded crossover fashion after 2 wk of adaptation to each formula. Isotope absorption studies were conducted with a 4-tracer method in which (70)Zn and (44)Ca were provided orally and (67)Zn and (46)Ca intravenously. Zinc and calcium absorption was measured from the fractional excretion of the oral and intravenous isotopes in urine.

RESULTS

Fractional and total calcium absorption was significantly greater from the lactose-containing formula than from the lactose-free formula. For total calcium absorption, the mean difference between formulas was 10.3% (P = 0.002) and 60 mg/d (P = 0.006). For zinc, fractional absorption (32 +/- 11%), total absorption, and intake did not differ significantly between the 2 formulas.

CONCLUSIONS

The presence of lactose in a formula based on cow-milk protein increases absorption of calcium but not of zinc. Absorption of calcium from a lactose-free infant formula is, however, adequate to meet the calcium needs of full-term infants when the formula's calcium content is similar to that of lactose-containing, cow-milk-based infant formulas.

Iron absorption in breast-fed infants: effects of age, iron status, iron supplements, and complementary foods

BACKGROUND

Iron supplements are often recommended for older breast-fed infants, but little is known about factors affecting iron absorption from human milk or supplements.

OBJECTIVE

We investigated the effects of age, iron status, and iron intake on iron absorption in healthy, term, breast-fed infants.

DESIGN

Twenty-five infants were randomly assigned to receive either 1) iron supplements (1 mg x kg(-1) x d(-1)) from 4 to 9 mo of age, 2) placebo from 4 to 6 mo and iron supplements from 6 to 9 mo, or 3) placebo from 4 to 9 mo. Infants were exclusively breast-fed to 6 mo and partially breast-fed to 9 mo of age. Iron absorption was assessed by giving (58)Fe with mother's milk at 6 and 9 mo. Blood samples were obtained at 4, 6, and 9 mo, and complementary food intake was recorded at 9 mo.

RESULTS

At 6 mo, mean (+/-SD) fractional iron absorption from human milk was relatively low (16.4 +/- 11.4%), with no significant difference between iron-supplemented and unsupplemented infants. At 9 mo, iron absorption from human milk remained low in iron-supplemented infants (16.9 +/- 9.3%) but was higher (P = 0.01) in unsupplemented infants (36.7 +/- 18.9%). Unexpectedly, iron absorption at 9 mo was not correlated with iron status but was significantly correlated with intake of dietary iron, including supplemental iron.

CONCLUSIONS

Changes in the regulation of iron absorption between 6 and 9 mo enhance the infant's ability to adapt to a low-iron diet and provide a mechanism by which some, but not all, infants avoid iron deficiency despite low iron intakes in late infancy.