Lily K. Liang

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.

Absorption by 1-year-old children of an iron supplement given with cow's milk or juice

A paucity of data are available on toddlers for the evaluation of optimal strategies of Fe supplementation. In this study, we used a two-tracer stable isotope technique to determine Fe absorption from a 5-mg dose of stable isotopically enriched (57Fe or 58Fe) ferrous sulfate given with cows milk (CM) compared with the same dose given with apple juice. Ten children (age 13 ± 1 mo, weight 10.8 ± 1.1 kg) who had recently discontinued formula feeding and begun on CM were studied. Red blood cell(RBC) iron incorporation of the isotope was determined 14 d after dosing with57 Fe and 58Fe. Fe absorption was calculated based on the assumption that 90% of absorbed Fe is incorporated into RBC. Absorption of Fe was significantly greater (13.7 ± 6.4%) when given with juice than with milk (5.7 ± 4.0%), p < 0.01 by paired t tests. Fe absorption from the dose given with juice was significantly negatively correlated with serum ferritin (n = 9, r = -0.70,p < 0.05). These results indicate that 1) a small supplement of Fe is better absorbed when given with juice than with CM, and 2) a large variability in Fe absorption exists in healthy 1-y-old infants, which is related to their existing Fe stores.

Variables related to urinary calcium excretion in young girls

The relations among dietary and calcium kinetic factors and 24-h urinary mineral excretion were evaluated in a group of 89 healthy girls (51 white and 38 black) aged 4.9-16.7 years. Nutrient intakes were calculated for each participant using a weighed intake of all food and beverage on the day of the 24-h urine collection study and two subsequent 24-h food records. A significant relation was noted between urinary calcium and sodium excretion (r = 0.55; p < 0.0001). No significant relations were found between urinary calcium and (a) calcium intake (r = 0.08), (b) protein intake (r = 0.14), or (c) phosphorus intake (r = 0.11). Urinary calcium was not significantly related to fractional calcium absorption (r = 0.03) or net calcium absorption (r = 0.11), but was significantly associated with the bone calcium deposition rate (r = 0.24; p < 0.03). Using a multiple regression model, both urinary sodium and the bone calcium deposition rate were independent predictors of urinary calcium excretion in this population (r = 0.57; p = 0.0001). A substantial number of the children in this population had urinary calcium excretion > 4 mg/kg/day (12%). The incidence of hypercalciuria differed between the racial groups and was markedly higher in the white than in the black children (17.6 vs. 5.3%). Over a range of usual calcium intakes, during the rapid-bone-growth period in childhood and early adolescence, urinary calcium appears relatively unaffected by calcium intake and is most strongly associated with urinary sodium levels.

Bone Turnover Response to Changes in Calcium Intake Is Altered in Girls and Adult Women in Families with Histories of Osteoporosis

Heredity and environmental factors contribute to the development of osteoporosis. Because calcium is the major mineral in bone and adolescence is a key period in bone acquisition, we hypothesized that bone turnover would be less responsive to alterations in dietary calcium intake in both girls and adult women from families with histories of osteoporosis. To address this issue, we studied calcium kinetics in the maternal grandmother (age range 56–81 years), mother (age range 32–47 years), and granddaughter (age range 8–15 years) in 10 multigenerational families. In five families, the mother and/or grandmother had osteoporosis (bone mineral density ≥ 2 SD below the age‐specific mean). To examine both active and passive calcium absorption, families consumed low‐ (279 ± 64 mg/day) and high‐ (1580 ± 385) calcium diets for 10 days prior to administration of oral (46Ca) and intravenous (42Ca) stable isotopes. Using repeated measures analysis of variance, fractional calcium absorption, true calcium absorption, bone calcium deposition, and the balance in bone calcium turnover were all significantly affected by diet (p < 0.01). Females from nonosteoporotic families had decreased bone calcium resorption with little change in bone calcium deposition during the high‐calcium study. In contrast, girls and adult women from osteoporotic families had increased both bone calcium deposition and resorption during the high‐calcium period, leading to a less positive balance in bone calcium turnover. A significant interaction between bone status and diet was found for bone calcium resorption (p < 0.05) and approached significance for bone calcium deposition (p < 0.07), effects which were independent of generation. We conclude that girls and women from osteoporotic families have a significantly altered bone turnover response to acute changes in calcium intake.

Zinc Metabolism in Adolescents with Crohn's Disease

Low serum zinc concentrations have been reported in Crohns 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.