Iron-fortified and unfortified cow's milk: effects on iron intakes and iron status in young children.

UNLABELLED: Iron intakes and iron status were evaluated in 36 young Swedish children given either iron-fortified or unfortified cow's milk. All children had good iron status and had received breast milk or iron-fortified formulae during infancy. Twenty 1-y-old children were randomized to a diet with iron-fortified milk (7.0 or 14.9 mg Fe l(-1) and 16 to a diet with unfortified milk. The iron intakes in the unfortified group at 15 and 18 mo (mean +/- SD 5.19 +/- 2.29 and 5.84 +/- 1.62 mg d(-1)) were low in relation to Nordic Nutrition Recommendations, while the intakes in the iron-fortified group (10.20 +/- 2.60 and 10.87 +/- 2.79mg d(-1)) were normal in relation to recommendations. The gain (increase) from receiving fortified diet during the study period was at most [upper limit for 95% confidence interval (CI)] 2.6 g l(-1) in blood haemoglobin, 1.9 fl in mean corpuscular volume, 2.7 micromol in serum iron and 4.5% in transferrin iron saturation, and the gain (decrease) was at most (lower limit for 95% CI) 0.29g l(-1) in serum transferrin and 0.9mg l(-1) in serum transferrin receptor (TfR). None of these differences was statistically significant. There was an almost significantly higher increase in serum ferritin (1.4 times higher relation of values at the end compared with the beginning, p = 0.06) and a significantly higher (1.2; p = 0.047) decrease in TfR/ log10 ferritin ratio in the fortified group. CONCLUSION: One-year-old children starting out with good iron status given either iron-fortified or unfortified cow's milk from 12 to 18 mo maintain sufficient iron status during this period. However, children fed unfortified cow's milk have an iron intake which is low in relation to recommendations and the quantitative development of their reserve iron in iron stores seems to be weaker than that of the fortified group. The consequences of this require further study.

Carbohydrate depletion has profound effects on the muscle amino acid and glucose metabolism during hyperinsulinaemia.

AIM: We investigated the effect of carbohydrate availability and euglycaemic hyperinsulinaemia on intramuscular and plasma amino acids in 14 healthy men (age 26.5 +/- 0.9 years, b.m.i. 22.9 +/- 0.5 kg/m2). METHODS: Insulin was infused (1.5 mU/kg/min) for 240 min both after a carbohydrate depleting exercise and after carbohydrate loading. Muscle samples were taken before and after hyperinsulinaemia. Plasma and intramuscular amino acid concentrations were measured. RESULTS: Insulin-mediated glucose disposal was similar after carbohydrate depletion (65.2 +/- 1.9 micromol/kg/min) and loading (66.9 +/- 2.8 micromol/kg/min). Carbohydrate depletion was associated with decreased alanine and increased branched chain amino acid (BCAA) concentrations in muscle and plasma. Blood lactate was lower after carbohydrate depletion (477 +/- 25 micromol/l) than loading (850 +/- 76 micromol/l, p < 0.001). In carbohydrate depletion, hyperinsulinaemia resulted in a greater increase in intramuscular (from 927 +/- 48 nmol/g muscle to 2029 +/- 104 nmol/g muscle, p < 0.001), than plasma (from 197 +/- 6.7 micromol/l to 267 +/- 11 micromol/l, p < 0.001) alanine. After carbohydrate loading muscle alanine did not rise significantly (from 1546 +/- 112 nmol/g muscle to 1781 +/- 71 nmol/g muscle) whereas plasma alanine decreased (from 339 +/- 26 micromol/l to 272 +/- 13 micromol/l, p < 0.05). CONCLUSIONS: (1) Carbohydrate availability has profound effects on the interrelationship between glucose and amino acid metabolism and on the form of storage for glucose-derived carbons. (2) For most amino acids changes in plasma levels of amino acids are not related to changes in concentrations of intramuscular amino acids during hyperinsulinaemia.

Higher concentrations of serum transferrin receptor in children than in adults.

BACKGROUND: The serum transferrin receptor (TfR) concentration in adults is suggested to provide a sensitive measure of iron depletion and together with the serum ferritin concentration to indicate the entire range of iron status, from iron deficiency to iron overload. However, little is known about TfR concentrations in children. OBJECTIVE: Our objective was to compare serum TfR and ferritin concentrations and their ratios in children and adults and look for correlations between TfR concentrations and other measures of iron status. DESIGN: Our study groups were healthy 1-y-old infants (n = 36), 11-12-y-old prepubertal boys (n = 35), and 20-39-y-old men (n = 40). RESULTS: TfR concentrations were higher in infants (x; 95% reference interval: 7.8 mg/L; 4.5, 11.1) than in prepubertal boys (7.0 mg/L; 4.7, 9.2) and higher in prepubertal boys than in men (5.8 mg/L; 3.1, 8.5). Geometric mean TfR-ferritin ratios were higher in infants (316; 95% reference interval: 94, 1059) than in prepubertal boys (219; 78, 614) and higher in prepubertal boys than in men (72; 23, 223). By multiple linear regression analysis, the best predictors of TfR concentration were serum iron (P = 0.004) and log serum ferritin (P < 0.0001), both being inverse correlations (R2 = 0.32). Mean corpuscular volume, blood hemoglobin, transferrin iron saturation, transferrin, and even age seemed to not have an influence on the TfR concentration and erythropoiesis was not a determinant of TfR concentration. CONCLUSIONS: Low serum ferritin and iron concentrations, even within the normal physiologic range, result in high TfR concentrations. The lower the iron stores, the stronger the influence of ferritin on TfR. A high TfR concentration in children, especially in infants, is a response to physiologically low iron stores. Age-specific reference concentrations for TfR are needed.