Prevalence of iron deficiency in the United States

OBJECTIVE

To determine the prevalence of iron deficiency and iron deficiency anemia in the US population.

DESIGN

Nationally representative cross-sectional health examination survey that included venous blood measurements of iron status.

MAIN OUTCOME MEASURES

Iron deficiency, defined as having an abnormal value for at least 2 of 3 laboratory tests of iron status (erythrocyte protoporphyrin, transferrin saturation, or serum ferritin); and iron deficiency anemia, defined as iron deficiency plus low hemoglobin.

PARTICIPANTS

A total of 24,894 persons aged 1 year and older examined in the third National Health and Nutrition Examination Survey (1988-1994).

RESULTS

Nine percent of toddlers aged 1 to 2 years and 9% to 11% of adolescent girls and women of childbearing age were iron deficient; of these, iron deficiency anemia was found in 3% and 2% to 5%, respectively. These prevalences correspond to approximately 700,000 toddlers and 7.8 million women with iron deficiency; of these, approximately 240,000 toddlers and 3.3 million women have iron deficiency anemia. Iron deficiency occurred in no more than 7% of older children or those older than 50 years, and in no more than 1% of teenage boys and young men. Among women of childbearing age, iron deficiency was more likely in those who are minority, low income, and multiparous.

CONCLUSION

Iron deficiency and iron deficiency anemia are still relatively common in toddlers, adolescent girls, and women of childbearing age.

Prevalence of iron deficiency in the United States

OBJECTIVE

To determine the prevalence of iron deficiency and iron deficiency anemia in the US population.

DESIGN

Nationally representative cross-sectional health examination survey that included venous blood measurements of iron status.

MAIN OUTCOME MEASURES

Iron deficiency, defined as having an abnormal value for at least 2 of 3 laboratory tests of iron status (erythrocyte protoporphyrin, transferrin saturation, or serum ferritin); and iron deficiency anemia, defined as iron deficiency plus low hemoglobin.

PARTICIPANTS

A total of 24,894 persons aged 1 year and older examined in the third National Health and Nutrition Examination Survey (1988-1994).

RESULTS

Nine percent of toddlers aged 1 to 2 years and 9% to 11% of adolescent girls and women of childbearing age were iron deficient; of these, iron deficiency anemia was found in 3% and 2% to 5%, respectively. These prevalences correspond to approximately 700,000 toddlers and 7.8 million women with iron deficiency; of these, approximately 240,000 toddlers and 3.3 million women have iron deficiency anemia. Iron deficiency occurred in no more than 7% of older children or those older than 50 years, and in no more than 1% of teenage boys and young men. Among women of childbearing age, iron deficiency was more likely in those who are minority, low income, and multiparous.

CONCLUSION

Iron deficiency and iron deficiency anemia are still relatively common in toddlers, adolescent girls, and women of childbearing age.

Maintenance of euglycemia is impaired in gluconeogenesis-inhibited iron-deficient rats at rest and during exercise

To evaluate the hypothesis that mild iron deficiency increases dependence upon gluconeogenesis, control and mildly iron-deficient (Hb = 80 +/- 2 g/L) rats were injected with mercaptopicolinic acid (MPA), a known inhibitor of gluconeogenesis, or with injection vehicle (sham) and studied at rest or after 30 min of treadmill running (13.4 m/min, 0% grade). Liver glycogen concentration was lower in resting iron-deficient rats than in resting control rats, but iron deficiency did not influence arterial substrates or hormones in sham-treated rats. Glucose and insulin concentrations were less in resting control and iron-deficient MPA-treated rats than in sham-treated animals. However, arterial lactate was greater in resting iron-deficient MPA-treated rats than control MPA-treated animals, and glucagon and epinephrine were greater in resting iron-deficient MPA-treated rats than in iron-deficient sham-treated animals, indicating that gluconeogenesis is more important to maintenance of euglycemia in resting iron-deficient animals than in controls. Moderate exercise stimulated glucose metabolism in iron-deficient rats, as evidenced by the lower arterial glucose and higher arterial lactate when compared with resting iron-deficient rats. However, MPA treatment did not clearly establish differences between iron-deficient and control rats after exercise. Therefore, changes in substrate and hormone concentrations in resting iron-deficient MPA-treated rats indicate that dependence on gluconeogenesis for maintenance of euglycemia is greater at rest with dietary iron deficiency. Furthermore, consistent with previously published results for severely iron-deficient rats, results from the present investigation indicate that dependence on glucose metabolism is greater during moderate exercise in mildly iron-deficient rats.

Augmented glucoregulatory hormone concentrations during exhausting exercise in mildly iron-deficient rats

We hypothesized that augmented responses of glucoregulatory hormones in iron deficiency would enhance liver and muscle glycogenolysis, leading to increased gluconeogenic precursor (lactate) supply and upregulation of hepatic gluconeogenesis. Female weanling rats were randomly placed on either a mildly iron-deficient (-Fe; 15 mg Fe/kg diet) or an iron-sufficient (+Fe; 50 mg Fe/kg diet) diet for 4 wk and studied at rest and during exhaustive treadmill running. Hemoglobin was 9.0 +/- 0.2 and 13.1 +/- 0.3 g/dl in -Fe and +Fe, respectively, after 3.5 wk of dietary iron deficiency. Arterial plasma epinephrine (Epi), norepinephrine (NE), adrenocorticotropic hormone (ACTH), corticosterone, insulin, and glucagon levels were similar at rest in both groups, as were liver, gastrocnemius, and superficial and deep vastus medialis glycogen levels. Liver and kidney phosphoenolpyruvate carboxykinase (PEPCK) activities were similar in both groups. Maximum O2 consumption was decreased (22%) in -Fe. Respiratory exchange ratio (CO2 production/O2 consumption) was unaffected at rest but increased at maximum O2 consumption in -Fe. Time to exhaustion during a standardized running test (13.4 m/min, 0% grade) was decreased 45% in -Fe (63 +/- 5 vs. 116 +/- 10 min). During exercise, euglycemia was maintained in both groups, but blood lactate was elevated in -Fe. The mean net glycogen utilization during exercise was increased in liver (43%), soleus (33%), and superficial vastus medialis (106%) and decreased in the gastrocnemius (36%) in -Fe. Liver and kidney PEPCK activities were increased similarly at exhaustion in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of iron-fortified infant cereal in prevention of iron deficiency anemia

BACKGROUND

Iron deficiency continues to be a common problem among infants throughout the world. Iron-fortified formula is effective in preventing iron deficiency but the benefit of iron-fortified cereal is controversial.

METHODS

We compared iron-fortified rice cereal to unfortified rice cereal in infants who were exclusively breast-fed for more than 4 months and to iron-fortified formula in infants who were weaned to formula before 4 months of age. The design was double blind in respect to the presence or absence of fortification iron in the cereal or formula and included 515 infants who were followed on the protocol from 4 to 15 months of age. Rice cereal was fortified with 55 mg of electrolytic iron per 100 g of dry cereal and infant formula with 12 mg of ferrous sulfate per 100 g of dry powder, levels approximating those in use in the United States. Measures of iron status were obtained at 8, 12, and 15 months. Infants with hemoglobin levels of < 105 g/L were excluded from the study and treated.

RESULTS

Consumption of cereal reached plateaus at means of about 30 g/d after 6 months of age in the formula-fed groups and 26 g/d after 8 months in the breast-fed groups; these amounts are higher than the 19-g/d mean intake by the 73% of infants who consume such cereal in the United States. Among infants weaned to formula before 4 months, the cumulative percentages of infants excluded for anemia by 15 months were 8%, 24%, and 4%, respectively, in the fortified cereal, unfortified cereal and formula, and fortified formula groups (P < .01 unfortified vs either fortified group; the difference between the two fortified groups was not significant). In infants breast-fed for more than 4 months, the corresponding values were 13% and 27%, respectively, in the fortified and unfortified cereal groups (P < .05). Mean hemoglobin level and other iron status measures were in accord with these findings.

CONCLUSION

Iron-fortified infant rice cereal can contribute substantially to preventing iron deficiency anemia.

Lactate is essential for maintenance of euglycemia in iron-deficient rats at rest and during exercise

To evaluate the hypothesis that lactate supply is essential to maintain euglycemia during iron deficiency, female Sprague-Dawley rats were assigned to iron-sufficient (50 mg Fe2+/kg diet, +Fe), or iron-deficient (15 mg Fe2+/kg diet, -Fe) dietary groups and were injected with a specific beta 2-adrenergic inhibitor, ICI 118,551 (1.0 mg/kg body wt). Rats were studied at rest or after 30 min of running at 13.4 m/min 0% grade. Dietary iron deficiency decreased hemoglobin concentration 38%, but resting arterial concentrations of glucose ([Glc]), lactate ([La]), or alanine ([Ala]) were unaffected. Administration of ICI 118,551 (beta 2-blockade) decreased [La] and [Glc] 52 and 32% in resting -Fe rats, respectively. beta 2-Blockade attenuated the exercise-induced rise in [La] and decreased [Glc] 31% in exercising -Fe rats. [Ala] were unaffected by iron deficiency or exercise but decreased 24 and 18% because of beta 2-blockade in resting and exercising +Fe rats. Iron deficiency depleted resting liver glycogen concentration 45%, with no additional effect of exercise or beta 2-blockade. beta-Blockade decreased arterial insulin and increased arterial glucagon concentrations in resting -Fe and +Fe rats. During exercise glucagon concentration increased significantly more in -Fe than +Fe rats. Decreased arterial [La] with a corresponding decrease in arterial [Glc] in response to beta 2-blockade support the contention that lactate supply is critical to maintenance of euglycemia in -Fe rats at rest and during exercise.

Hepatic adaptations to iron deficiency and exercise training

Brooks et al. [Am. J. Physiol. 253 (Endocrinol. Metab. 16): E461-E466, 1987] demonstrated an elevated gluconeogenic rate in resting iron-deficient rats. Because physical exercise also imposes demand on this hepatic function, we hypothesized that exercise training superimposed on iron deficiency would augment the hepatic capacity for amino acid transamination/deamination and pyruvate carboxylation. Sprague-Dawley rats (n = 32) were obtained at weaning (21 days of age) and randomly assigned to iron-sufficient (dietary iron = 60 mg iron/kg diet) or iron-deficient (3 mg iron/kg) dietary groups. Dietary groups were subdivided into sedentary and trained subgroups. Treadmill training was 4 wk in duration, 6 days/wk, 1 h/day, 0% grade. Treadmill speed was initially 26.8 m/min and was decreased to 14.3 m/min over the 4-wk training period. The mild exercise-training regimen did not affect any measured variable in iron-sufficient rats. In contrast, in iron-deficient animals, training increased endurance capacity threefold and reduced blood lactate and the lactate-to-alanine ratio during submaximal exercise by 34 and 27%, respectively. The mitochondrial oxidative capacity of gastrocnemius muscle was increased 46% by training. However, the oxidative capacity of liver was not affected by either iron deficiency or training. Maximal rates of pyruvate carboxylation and glutamine metabolism by isolated liver mitochondria were also evaluated. Iron deficiency and training interacted to increase pyruvate carboxylation by intact mitochondria. Glutamine metabolism was increased roughly threefold by iron deficiency alone, and training amplified this effect to a ninefold increase over iron-sufficient animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Iron status with different infant feeding regimens: relevance to screening and prevention of iron deficiency

The objective of this study was to evaluate the benefit of screening for anemia in infants in relation to their previous diet. The iron status of 854 nine-month-old infants on three different feeding regimens and on a regimen including iron dextran injection was determined by analysis of hemoglobin, serum ferritin, and erythrocyte protoporphyrin levels and of serum transferrin saturation. Infants were categorized as having iron deficiency if two or three of the three biochemical test results were abnormal and as having iron deficiency anemia if, in addition, the hemoglobin level was less than 110 gm/L. The prevalence of iron deficiency was highest in infants fed cow milk formula without added iron (37.5%), intermediate in the group fed human milk (26.5%), much lower in those fed cow milk formula with added iron (8.0%), and virtually absent in those injected with iron dextran (1.3%). The corresponding values for iron deficiency anemia were 20.2%, 14.7%, 0.6%, and 0%, respectively. The use of iron supplements is therefore justified in infants fed cow milk formula without added iron, even when there is no biochemical evidence of iron deficiency. The low prevalence of iron deficiency in the group fed iron-fortified formula appears to make it unnecessary to screen routinely for anemia in such infants. These results also support the recommendation that infants who are exclusively fed human milk for 9 months need an additional source of iron after about 6 months of age.

Iron deficiency: improved exercise performance within 15 hours of iron treatment in rats

We tested the hypothesis that a very rapid improvement in exercise performance of iron-deficient rats after treatment with iron might reveal a rate-limiting role of ionic iron as an enzyme cofactor in energy metabolism. Rats were given iron-deficient or control diets after weaning at 21 d of age and intraperitoneal iron dextran (50 mg/kg) at 45 d of age. Time to fatigue during an easy walking exercise (endurance) was measured 15 and 18 h after iron dextran or saline injection. Endurance increased more than threefold compared to the saline-treated, iron-deficient animals without a significant change in hemoglobin concentration. This prompt improvement suggests that lack of cofactor iron might play a metabolically important role in impairing exercise performance in the severely iron-deficient rat.

Progress in the prevention of iron deficiency in infants

Our present success in preventing iron deficiency in infants is based on a gradual growth in our understanding of iron nutrition. It became recognized that full term infants only become vulnerable to iron deficiency after about 5 months of age, and to a lesser degree if they are breast-fed. The specific foods in which iron is provided during infancy were found to be more important in determining iron absorption than the actual amount of iron in the diet. Experience has also shown that fortification of infant foods is more reliable and cost effective than providing iron medication. Our current approaches to preventing iron deficiency in infants include: 1) maintaining breast feeding for at least 6 months, if possible; 2) using an iron-fortified infant formula if a formula is used and using formula in preference to cow's milk; 3) using iron-fortified infant cereal as one of the first solid foods; and 4) providing supplemental iron for low birth weight infants.

Muscle mitochondrial ultrastructure in exercise-trained iron-deficient rats

To investigate effects of endurance training and iron deficiency, as well as the combination of these two conditions, on mitochondrial ultrastructure, weanling rats at 3 wk of age were assigned to iron-deficient (Fe-) and iron-sufficient (Fe+) groups. Subsequently, groups were subdivided into exercise-trained (T) and sedentary (S) groups. Electron microscopy showed subsarcolemmal and intrafibrillar mitochondria in the Fe-T animals to be enlarged with sparse cristae and vacuole-like areas compared with the other groups. An increase in the number of lipid droplets in both Fe- groups was observed. Stereological measurements revealed a 99% increase in the volume occupied by muscle mitochondria in the Fe-T animals (11.9 +/- 0.8%) over the Fe+T (5.9 +/- 0.4%) and Fe+S (6.0 +/- 0.3%) groups and a 55% increase over the Fe-S groups (7.7 +/- 0.3%). The ratio of mitochondrial surface area to tissue volume was significantly decreased only in the Fe-T group. These results indicate that the combined stresses of iron deficiency and training produce mitochondrial ultrastructural changes far greater than those of iron deficiency or training alone. Because this is also the case with the disproportion among mitochondrial enzymes, it is possible that the ultrastructural changes are indicative of morphological responses that maintain ATP turnover during exercise in iron deficiency when oxygen transport and electron transport chain activities are reduced.

Upper limits of iron in infant formulas

Iron-fortified infant formula is effective in preventing iron deficiency at levels of iron that are compatible with an upper limit of 3 mg/100 kcal. However, lower levels of fortification may prove to be adequate. There are theoretical concerns about the effects of high levels of dietary iron on the absorption of other trace minerals and on resistance to infection. These considerations make it desirable to determine whether lower levels of iron fortification in infant formula will be equally effective in preventing iron deficiency in infants.

Impaired control of respiration in iron-deficient muscle mitochondria

Dietary iron deficiency (ID) decreases iron-containing proteins and hence respiratory capacity of skeletal muscle mitochondria (SMM), but noniron components are much less affected. Using a hexokinase plus glucose ATP-utilizing system, we studied control of respiration in isolated SMM from rats of variable iron status: ID, ID 3 days after intraperitoneal treatment with iron dextran, and control. We found that sensitivity of respiratory control (e.g., ATP/ADP at a given oxygen consumption) was positively related to state 3 respiratory capacity. Titration studies with carboxyatractyloside, a noncompetitive inhibitor of adenine nucleotide translocase (AdNT), revealed that AdNT concentration was unaffected by iron status. However, the turnover number of AdNT was markedly reduced by ID and improved with iron treatment. We conclude that in ID SMM, decreased maximal respiratory capacity is paralleled by impaired sensitivity to putative controllers of oxidative phosphorylation at any respiratory rate, despite normal levels of AdNT. A second study was designed to determine possible consequences of impaired sensitivity of respiratory control on motor unit recruitment during exercise. ID and normal rats were subjected to a program of walking treadmill exercise. Although exercise failed to induce any changes in oxidative enzyme levels in control rat, ID animals and exhibited substantial mitochondrial enzyme adaptation in hindlimb skeletal muscle. Furthermore, the most consistent enzymatic changes were observed to occur in fast glycolytic muscle fibers. These results suggest marked alterations in the pattern of muscle fiber recruitment during mild exercise in ID rodents and support the hypothesis that sensitivity of respiratory control in SMM is an important determinant of motor unit recruitment during aerobic exercise.

Iron deficiency decreases gluconeogenesis in isolated rat hepatocytes

Dietary iron deficiency in rats results in increased blood glucose turnover and recycling. We measured the rates of glucose production in isolated hepatocytes from iron-sufficient (Fe+) and iron-deficient (Fe-) rats to assess the intrinsic capacity of the Fe- liver to carry out gluconeogenesis. Low-iron and control diets were given to 21-day-old female rats. After 4-5 wk, hemoglobin concentrations averaged 4.1 g/dl in the Fe- and 14.3 g/dl in the Fe+ animals. In the hepatocytes from Fe- rats, there was a 35% decrease in the rate of glucose production from 1 mM pyruvate + 10 mM lactate, a 48% decrease from 0.1 mM pyruvate + 1 mM lactate, a 39% decrease from 1 mM alanine, and a 48% decrease from 1 mM glycerol. The addition of 5 microM norepinephrine or 0.5 microM glucagon to the incubation media produced stimulatory effects on hepatocytes from both Fe- and Fe+ rats, resulting in the maintenance of an average difference of 38% in the rates of gluconeogenesis between the two groups. Studies on isolated liver mitochondria and cytosol revealed alpha-glycerophosphate-cytochrome c reductase and phospho(enol)pyruvate carboxykinase activities to be decreased by 27% in Fe- rats. We conclude that because severe dietary iron deficiency decreases gluconeogenesis in isolated rat hepatocytes, the increased gluconeogenesis demonstrated by Fe- rats in vivo is attributable to increased availability of gluconeogenic substrates and upregulation of the pathway.

Iron deficiency: does it matter?

Iron deficiency causes different abnormalities in the three major population groups that are at risk. In pregnant women, epidemiological studies suggest that anaemia, presumably due mainly to iron deficiency, is associated with an increased risk of low birth weight, prematurity, and perinatal mortality. In iron-deficient infants and children, there is convincing evidence of impaired psychomotor development and cognitive performance. Finally, iron-deficient women during the childbearing years (and iron-deficient men) have a decreased work capacity and less efficient response to exercise. These symptoms provide ample justification for preventing and treating a common and easily correctable nutritional disorder.

Reciprocal changes of muscle oxidases and liver enzymes with recovery from iron deficiency

We determined the recovery time courses of muscle oxidases and liver enzymes after iron administration to iron-deficient rats. Female 21-day-old Sprague-Dawley rats were fed an iron-deficient (3 mg Fe/kg) or a control (50 mg Fe/kg) diet for 3 wk. The deficient rats were then injected with 50 mg Fe as iron dextran/kg body wt (Fe-T) or saline (Fe-) intraperitoneally. At 16, 40, 64, 112, and 180 h after injection, blood and tissue samples were taken to determine hemoglobin concentration (Hb), gastrocnemius glycolytic enzyme and oxidase activities, and liver amino acid catabolic enzyme activities. No changes were observed in any parameter across time in either the Fe- or control (Fe+) rats. In the Fe- rats, Hb, pyruvate + malate (P + M), 2-oxoglutarate (2-OG), and succinate oxidases (SO) were depressed to 33, 36, 44, and 7% of Fe+, respectively (P less than 0.05). At 16 h, Fe-T values were significantly elevated compared with Fe- rats but still only 40, 48, 55 and 10% of controls, respectively. Glutamate dehydrogenase (GDH) and alanine aminotransferase (AAT) of Fe- rats were 174 and 134% of control values (P less than 0.05). By the 180-h time point, Hb, P + M, 2-OG, and SO of Fe-T rats increased to 99, 84, 89, and 43% of Fe+ values, whereas GDH and AAT activities declined to 111 and 106% of controls. Glycolytic enzymes showed no systematic changes with iron deficiency or after iron administration.(ABSTRACT TRUNCATED AT 250 WORDS)

The roles of inflammation and iron deficiency as causes of anemia

Inflammatory disease as well as iron deficiency may play an important role in the cause of anemia in the United States. We evaluated the relationships between Fe deficiency, inflammatory disease, and anemia using data from of the First National Health and Nutritional Examination Survey (NHANES I). Fe nutrition index was based on the ratio of serum Fe to Fe-binding capacity (Fe:TIBC) and inflammatory index was based on erythrocyte sedimentation rate (ESR). Groups with the highest prevalence of anemia were younger children, young women, and elderly men. Fe deficiency (low Fe:TIBC) was most common among the anemic children and young women but rare in anemic elderly men. Conversely, inflammation (high ESR) was most common among anemic elderly individuals. The prevalence of anemia was more than twice as high in the lowest than in the highest income group. Relative contributions of Fe deficiency and inflammation to anemia did not differ substantially among income groups.

Physiological and biochemical correlates of increased work in trained iron-deficient rats

We investigated physiological and biochemical factors associated with the improved work capacity of trained iron-deficient rats. Female 21-day-old rats were assigned to one of four groups, two dietary groups (50 and 6 ppm dietary iron) subdivided into two levels of activity (sedentary and treadmill trained). Iron deficiency decreased hemoglobin (61%), maximal O2 uptake. (VO2max) (40%), skeletal muscle mitochondrial oxidase activities (59-90%), and running endurance (94%). In contrast, activities of tricarboxylic acid (TCA) cycle enzymes in skeletal muscle were largely unaffected. Four weeks of mild training in iron-deficient rats resulted in improved blood lactate homeostasis during exercise and increased VO2max (15%), TCA cycle enzymes of skeletal muscle (27-58%) and heart (29%), and liver NADH oxidase (34%) but did not affect any of these parameters in the iron-sufficient animals. In iron-deficient rats training affected neither the blood hemoglobin level nor any measured iron-dependent enzyme pathway of skeletal muscle but substantially increased endurance (230%). We conclude that the training-induced increase in endurance in iron-deficient rats may be related to cardiovascular improvements, elevations in liver oxidative capacity, and increases in the activities of oxidative enzymes that do not contain iron in skeletal and cardiac muscle.

Increased glucose dependence in resting, iron-deficient rats

Rates of blood glucose and lactate turnover were assessed in resting iron-deficient and iron-sufficient (control) rats to test the hypothesis that dependence on glucose metabolism is increased in iron deficiency. Male Sprague-Dawley rats, 21 days old, were fed a diet containing either 6 mg iron/kg feed (iron-deficient group) or 50 mg iron/kg feed (iron-sufficient group) for 3-4 wk. The iron-deficient group became anemic, with hemoglobin levels of 6.4 +/- 0.2 compared with 13.8 +/- 0.3 g/dl for controls. Rats received a 90-min primed continuous infusion of D-[6-3H]glucose and sodium L-[U-14C]lactate via a jugular catheter. Serial samples were taken from a carotid catheter for concentration and specific activity determinations. Iron-deficient rats had significantly (P less than 0.05) higher blood glucose (7.1 +/- 0.3 vs. 6.1 +/- 0.2 mM) and lactate concentrations than controls (1.0 +/- 0.1 vs. 0.8 +/- 0.1 mM). The iron-deficient group had a significantly higher glucose turnover rate (67 +/- 2 vs. 58 +/- 4 mumol . kg-1 . min-1) than the control group. Significantly more metabolite recycling in iron-deficient rats was indicated by greater incorporation of 14C (from infused [14C]-lactate) into blood glucose. Assuming a carbon crossover correction factor of 2, half of blood glucose arose from lactate in deficient animals. By comparison, only 25% of glucose arose from lactate in controls. Lack of a difference in lactate turnover (irreversible disposal) rates between deficient rats and controls (191 +/- 26 vs. 163 +/- 15 mumol . kg-1 . min-1) was attributed to 14C recycling.(ABSTRACT TRUNCATED AT 250 WORDS)

Iron deficiency and the immune response

The importance of iron deficiency as a public health problem is based ultimately on the seriousness of its consequences on health. The most extensively investigated consequences of iron deficiency involve work performance and immune function. The significance of the effects on work performance are generally accepted. In contrast, data on the influence of iron deficiency on immune function are often perceived as being confusing and contradictory. From reexamination of relevant literature, it seems safe to conclude that abnormalities in cell-mediated immunity and ability of neutrophils to kill several types of bacteria are well established under experimental conditions in iron-deficient patients. It remains uncertain whether these abnormalities result in an increased incidence and duration of infections. This area still requires careful study.

sIgA- and IgM-containing cells in the intestinal mucosa of iron-deficient rats

The effect of iron deficiency on the jejunal mucosa was studied in postweaning rats that had received a 3-wk regimen of either iron-deficient or iron-sufficient diet (iron content 6 and 50 mg/kg diet) and in rats given the iron-sufficient diet for 1 wk after the initial 3-wk iron-deficient diet. Morphometric analysis showed little difference in villous height but a significant decrease in mitotic index of the crypt epithelial cells in the iron-deficient group. Direct immunoperoxidase studies showed that iron-deficient rats had substantially fewer sIgA- and IgM-containing cells than iron-sufficient rats. This abnormality was reversed after a 1-wk iron-sufficient diet. We conclude that iron deficiency may impair local immunity in the intestinal mucosa, sensitizing the surface epithelial cells to damage by noxious agents. Similar changes might lead to the syndrome of iron-deficiency anemia and hypoproteinemia in children.

Effects of iron deficiency and training on mitochondrial enzymes in skeletal muscle

We measured mitochondrial enzyme activities in skeletal muscle under conditions of iron deficiency and endurance training to assess the effects of these interventions on the contents and proportions of non-iron-containing and iron-dependent enzymes and proteins. Male Sprague-Dawley rats, 21 days of age, received a diet containing either 6 (iron deficient) or 50 mg iron/kg diet (iron sufficient). At 35 days of age animals were subdivided into sedentary and endurance training groups (running at 0.7 mph, 0% grade, 45 min/day, 6 days/wk). By 70 days of age, iron deficiency had decreased gastrocnemius muscle cytochrome c by 62% in sedentary animals. In contrast, the activities of tricarboxylic acid cycle enzymes were increased, remained unchanged or were slightly decreased, indicating that iron deficiency markedly altered mitochondrial composition. Endurance training increased cytochrome c (35%), tricarboxylic acid cycle enzymes (approximately 15%), and manganese superoxide dismutase (33%) in iron-deficient rats, whereas the same exercise regimen had no effect on the skeletal muscle of iron-sufficient animals. The interactive effect of dietary iron deficiency and mild exercise on mitochondrial enzymes suggests that adaptation to a training stimulus is, to some extent, geared to the relationship between the energy demand of exercise and the capacity for O2 transport and utilization.

Iron deficiency and neutrophil function: different rates of correction of the depressions in oxidative burst and myeloperoxidase activity after iron treatment

The polymorphonuclear granulocyte (PMN) kills ingested bacteria by mechanisms that include myeloperoxidase (MPO) and a sudden increase in oxygen consumption (the oxidative burst), both of which are iron dependent. The magnitude of the oxidative burst and activity of MPO were determined in PMNs during the progression of iron deficiency (ID) and following its treatment in rats. As ID developed, the oxidative burst after zymosan activation was less depressed than the activity of MPO. There was no change in the oxidative burst after activation with phorbol myristate acetate (PMA) or in the generation of superoxide (O2-) by NADPH oxidase-containing particles from PMNs. Following iron treatment, impairment of the oxidative burst after zymosan activation was corrected after 1 day. In contrast, the deficit in MPO activity was not corrected until 7 days after initiation of iron treatment. The pattern of recovery in MPO activity after iron treatment corresponded to the prolonged period of maturation of the PMN primary granule since the formation of primary granules, which contain MPO, takes place only in the early, mitotic stages of maturation. The tendency of the PMN to maintain the oxidative burst allows the cell to preserve its capacity for bacterial killing during the progression of iron deficiency.

Serum erythropoietin levels in patients with congenital heart disease

Serum erythropoietin levels were measured by radioimmunoassay in 146 children and young adults with congenital heart disease to assess the relationship between erythropoietin and clinical factors (heart failure, anemia, cyanosis) and hemodynamic variables affecting oxygen delivery and utilization. Erythropoietin values were in the normal range (10 to 30 microU/mL) in 73% (58 of 80) of the patients with and 82% (54 of 66) of those without cyanosis. Elevated erythropoietin values in cyanotic patients were associated with lower mixed venous oxygen saturation and tension than in cyanotic patients with normal erythropoietin levels, even though the degree of polycythemia was similar. In contrast, most of the acyanotic patients who had elevated erythropoietin levels were anemic. Of the blood oxygen measurements, mixed venous oxygen saturation and tension had the closest inverse correlation with erythropoietin values. The normal erythropoietin values in most patients are in accord with other observations that show that an elevation in erythropoietin level in response to hypoxia will be transient if it results in a rise in hemoglobin concentration "appropriate" to the degree of hypoxia. Persistent elevation of erythropoietin in patients with congenital heart disease may indicate harmful impairment of hemoglobin production that is potentially correctable.

Anemia in children with acute infections seen in a primary care pediatric outpatient clinic

Anemia is a recognized feature of chronic disease and severe acute infection in hospitalized children. The purpose of this study was to determine the association of anemia with manifestations of infection in an unselected group of children seen as outpatients. The group consisted of 1347 children between the ages of 0.5 and 12 years that were seen over a 3-month period. Anemia was detected in 17% of the children ages 6 to 47 months (hemoglobin (Hgb) less than 11.0 g/dl) and in 5% of the children between 4 and 12 years of age (Hgb less than 11.5 g/dl). The prevalence of anemia was strongly associated with the degree of inflammation as indicated by the erythrocyte sedimentation rate (ESR). Of those children ages 6 to 47 months with an ESR greater than or equal to 50 mm/hour, 91% had Hgb less than 11.0 g/dl and 52% had Hgb less than 10.0 mg/dl. In contrast anemia (Hgb less than 11.0 g/dl) was rare (9%) in the group with ESRs of 0 to 19 mm. The corresponding prevalences of anemia in other ESR categories were 49% with ESR 40 to 49 mm/hour, 28% with ESR 30 to 39 mm/hour and 16% with ESR 20 to 29 mm/hour. There was also a significant association of anemia with the duration of fever in the children ages 6 to 47 months with ESR greater than or equal to 40 mm. The results show that anemia was commonly associated with the usually mild infections that are typically seen in a pediatric primary care setting. The anemia could be inferred to be reversible and unrelated to iron deficiency in most cases.

Glucose turnover and oxidation are increased in the iron-deficient anemic rat

To test the hypothesis that glucose metabolism is altered by iron deficiency, rates of glucose turnover and oxidation were assessed concurrently with the metabolic rate (VO2) in iron-deficient anemic rats and in normal rats at rest. Male Sprague-Dawley rats, 21 days old, were fed a diet containing either 6 mg iron/kg feed (iron-deficient group) or 50 mg iron/kg feed (iron-sufficient control group) for 3-4 wk. After dietary treatment the iron-deficient group was anemic, with hemoglobin levels of 5.8 +/- 0.2 g/dl, compared with 13.8 +/- 0.4 g/dl for controls. To study glucose metabolism, rats received a 90 min primed-continuous infusion of [6-3H]-and [U-14C]glucose via an indwelling jugular catheter. Serial blood samples were removed from a carotid catheter for determination of glucose concentration and specific activity. Expired air was monitored for VO2, VCO2, and 14CO2. The VO2 (ml X kg-1 X min-1) of iron-deficient rats was 20% higher than controls. Iron-deficient rats had a greater rate of glucose turnover (94 +/- 4 vs. 52 +/- 3 mumol X kg-1 X min-1) and a greater glucose recycling rate, even when normalized to VO2. Despite a higher blood glucose concentration (5.5 +/- 0.6 vs. 4.1 +/- 0.1 mM), the metabolic clearance rate was greater in iron-deficient animals (18 +/- 1 vs. 13 +/- 1 ml X kg-1 X min-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Iron deficiency in the weanling: a nutritional problem on the way to resolution

The rapidly growing weanling becomes vulnerable to iron deficiency when neonatal iron stores have been consumed after the first few months following birth. Whether the infant will progress from the harmless condition of depleted iron stores to the physiological handicaps associated with iron deficiency depends on the selection of foods during the period of weaning. Consumption of fresh cow's milk and of unfortified cow's milk formulas and cereal products predispose to iron deficiency. Breast feeding, iron- and ascorbic acid-fortified cow's milk formulas and cereals, and the use of ascorbic acid-rich foods and meat decrease the likelihood of iron deficiency. Recent changes in infant feeding practices in the United States have been associated with a marked decline in iron deficiency anemia. A challenge for the future will be to extend this success, particularly to developing countries.

Does iron supplementation compromise zinc nutrition in healthy infants?

Iron supplements are commonly administered to infants in order to prevent iron deficiency. We wished to determine whether iron administration could compromise zinc nutrition as might be suspected from previous studies. Measures of iron nutrition, serum zinc, and serum copper were measured before and after randomization of 291 healthy 1-yr-old infants to a 3 mo course of placebo or iron treatment (30 mg iron as ferrous sulfate given before a meal). There was no significant difference in serum zinc or copper in the two groups before or after treatment; thus iron administration did not result in any evidence of zinc deficiency in a healthy, well-nourished group of T-yr-old infants.

Work performance in the iron-deficient rat: improved endurance with exercise training

The effect of an endurance training regimen on muscle oxidative enzymes and work performance was studied in iron-deficient and -sufficient rats. Three-week-old male Sprague-Dawley rats (n = 40) were randomly assigned to diets containing either 6 mg iron/kg (iron deficient) or 50 mg iron/kg (iron sufficient). After 2 wk, each group of rats was further divided into untrained or endurance-trained subgroups. Training consisted of daily treadmill running of gradually increasing duration for a 1-mo period. After the training period, sedentary and endurance-trained iron-deficient rats were anemic (Hgb approximately 8 g/dl compared with 16 g/dl in the 2 control groups) and had significantly lower skeletal muscle cytochrome c concentration, cytochrome oxidase activity, and succinic oxidase activity compared with the iron-sufficient groups. In response to training iron-deficient rats also generally had a substantial increase in skeletal muscle oxidative enzymes (P less than 0.05), in contrast to iron-sufficient animals, in which there was little or no training effect. Work performance in response to training in the iron-deficient rats improved more than sixfold in an endurance type of exercise (P less than 0.05), but maximal oxygen consumption during a brief, intense type of exercise was not significantly affected. The results suggest that endurance training of iron-deficient rats results in a milder anemia and less drastic reduction of skeletal muscle oxidative enzymes which in turn allows better performance in an endurance type of exercise.

Urinary catecholamines in iron-deficient rats at rest and following surgical stress

The purpose of this study was to determine catecholamine concentrations both at rest and in response to a surgical stress in iron-deficient and control rats. Twenty-one-day-old rats were randomized to one of two groups which received a diet containing either 6 or 50 mg iron/kg. Three to five days later, when anemia was first detectable, urinary norepinephrine (NE) concentrations were already significantly elevated in the iron-deficient compared to control rats. In contrast, urinary dopamine (DA) became depressed after 10 days of the iron-deficient regimen. At 38 days of age, both groups were subjected to a surgical stress. NE and DA became elevated over baseline values in both diet groups during the 24-h period following surgery; NE remained significantly higher and DA significantly lower in the iron-deficient than in the control group. We conclude that changes in urine catecholamine concentration occur early in the development of iron deficiency and that they are characteristic of both baseline and stress conditions.

Work performance in iron deficiency of increasing severity

The effect of iron deficiency on work capacity was studied in groups of rats that had received diets with iron contents ranging between 9 and 50 mg/kg diet from 3 to 6 wk of age. Maximal O2 consumption (VO2max) declined only 16% with a decrease in hemoglobin (Hb) from 14 to 8 g/dl and fell sharply only below a Hb of 7 g/dl. Duration until exhaustion in a treadmill exercise of submaximal intensity (endurance) showed no significant depression between a Hb of 14 and 10 g/dl. However, endurance declined abruptly by 73% between a Hb of 10 and 8 g/dl. The VO2max results are in accord with known compensatory mechanisms that help to maintain delivery of O2 to tissues until anemia becomes severe. The sharp fall in endurance with relatively mild iron deficiency suggests a lack of similarly effective compensations for decreased oxidative capacity of muscle.

Erythropoietin concentration during the development and recovery from iron deficiency in the rat

The concentration of plasma erythropoietin was determined by radioimmunoassay during the progression of and subsequent recovery from iron-deficiency anemia in the rat. During the development of anemia, the plasma erythropoietin level rose as the hemoglobin (Hgb) concentration declined, reaching maximal levels when the Hgb was lowest. During the recovery from iron-deficiency anemia after institution of the control diet, the plasma erythropoietin concentration rapidly declined to baseline or below baseline levels even before the Hgb had completely returned to control values. This early fall in the erythropoietin level was associated with a sustained decrease in blood oxygen affinity (increase in P50). The rise in P50 was associated with an increase in the number of circulating reticulocytes in addition to and independently of an increase in the concentration of 2,3-diphosphoglycerate (DPG) in red cells. Therefore, reticulocytosis may play a part in the recovery from anemia, not only by replenishing the red cell pool but also by temporarily facilitating oxygen delivery to the tissues.

Postnatal changes in fetal hemoglobin, oxygen affinity and 2,3-diphosphoglycerate in previously transfused preterm infants

We observed a temporary rise in the percentage of fetal hemoglobin (HbF%) in small preterm infants after cessation of frequent replacement transfusions. We prospectively studied 10 very low birthweight infants, who received frequent transfusions in the first several weeks of life, to determine the influence on oxygen affinity (P50). After cessation of frequent transfusions, those 5 infants whose HbF% increased to the highest values (mean 58%) had a lower oxygen affinity (P50 = 23.3 Torr, p less than 0.05) than the remaining 5 infants whose increase in HbF% was less marked, to an average of only 29% (P50 = 24.5 Torr). However, in light of the small difference in P50, we feel that a rise in HbF% by itself after a period of frequent transfusions is unlikely to restrict oxygen delivery except under stressful conditions.

Red cell superoxide dismutase is increased in iron deficiency anemia

Red blood cells (RBC) from iron-deficient rats were found to generate more malonyldialdehyde after in vitro incubation with H2O2 than RBC from control rats (p less than 0.001). The iron-deficient RBC, however, had a higher content of superoxide dismutase (SOD) than control RBC (p less than 0.02). This finding suggests an increased formation of SOD compensatory to an increased oxidant stress.

Iron deficiency in infants: the influence of mild antecedent infection

In this study of 467 healthy term infants seen for routine 1-year health maintenance examination, we determined the influence of mild prior infection on the concentration of hemoglobin and other laboratory evidence of iron deficiency. In addition we studied the Hgb response in 261 infants randomized to receive a 3-month course of treatment with either iron or placebo. Infants who had had one or more clinic visits because of infection during the previous 3 months or who were reported as not being entirely well during the past month or who had an elevated sedimentation rate were more likely to have anemia or "low normal" Hgb, higher erythrocyte protoporphyrin and serum ferritin values, and lower serum iron concentration than infants who had been well. Hgb response greater than or equal to 1 gm/dl after iron treatment occurred more commonly in infants who had had prior visits because of infection. The results indicate that upper respiratory and other mild antecedent infections commonly predispose to iron deficiency (probably because of a decrease in iron absorption).

Decreased response of plasma immunoreactive erythropoietin to "available oxygen" in anemia of prematurity

Erythropoietin, hemoglobin, hematocrit, oxygen affinity (P50), and reticulocyte counts were measured weekly starting at 1 week of age in 10 very-low-birth-weight infants and on a single occasion in 15 healthy men. In the adults, "available oxygen" (derived from oxygen carrying capacity and P50) averaged 13.1 ml/dl blood and the mean erythropoietin level was 15.2 mU/ml. Erythropoietin levels in the infants were inversely related to concentration of hemoglobin, P50, and available oxygen. However, despite the much lower mean "available oxygen" of 9.3 ml/dl in the infants compared with that in adults (P less than 0.001), the mean erythropoietin value of 8.2 mU/ml in the infants was less than in adults (P less than 0.001). Furthermore, the erythropoietin response to decreased "available oxygen" was lowest in the least mature infants. VLBW infants often develop clinical evidence of hypoxia during the anemia of prematurity. The relatively low erythropoietin levels in relation to "available oxygen" are compatible with a decreased erythropoietin response to hypoxia compared with that in adults. Such a difference in response could be a contributing factor to the anemia of prematurity.

The pituitary-adrenal response to stress in the iron-deficient rat

This study was designed to determine the ACTH-corticosterone response to two types of stress in relation to the daily rhythm of food and water intake in the iron-deficient rat. Rats were fed diets containing 2, 10 or 50 mg iron/kg diet between weaning at 21 days and the stress experiments at 38 or 42 days of age. The two iron-deficient diets (2 and 10 mg iron/kg) resulted in mean hemoglobin concentrations of about 6.0 and 8.5 g/dl, respectively, in contrast to about 12.5 g/dl in the control group receiving 50 mg iron/kg diet. Food and water consumption followed the normal nocturnal pattern, irrespective of iron intake. ACTH and corticosterone showed the normal baseline peaks at the 2000 hour lights-out point in all groups. Responses to handling and placement into another cage were similar in most respects but suggested an inappropriately low corticosterone response despite high ACTH values only at the 2000 hour point. However, there was no evidence of similar differences in response to the more potent stress of an i.p. injection of histamine 1 mg/100 g body weight. In contrast to the reports of more clear-cut effects of iron deficiency on norepinephrine, the changes in ACTH and corticosterone response to stress seem relatively modest.

Effect of iron deficiency on succinate- and NADH-ubiquinone oxidoreductases in skeletal muscle mitochondria

The effects of iron deficiency on the NADH- and succinate-oxidizing complexes of rat skeletal muscle mitochondria have been investigated. Both systems were similarly affected: activities were about 30% of normal in dehydrogenase, ubiquinone reductase, and oxidase assays, and similar reductions in the concentration of their respective flavin prosthetic groups were also evident in the iron-deficient membranes. Thus, the turnover numbers of the two enzymes were unchanged in iron deficiency. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed similarly reduced levels of those peptide components of Complexes I and II that could be unequivocally distinguished. Soluble beef heart succinate dehydrogenase added to alkaline-treated rat skeletal muscle mitochondrial membranes attached to binding sites exposed by the treatment, forming a hybrid complex indistinguishable from the original skeletal muscle complex, with restoration of succinoxidase and succinate-ubiquinone reductase activities to the levels observed in the original rat membranes. Iron-deficient particles behaved like the normal in these tests. No unfilled binding sites for the enzyme could be detected prior to alkaline treatment. The data are interpreted as indicating that the lower activities of these two respiratory complexes in iron deficiency are due to lower content of the enzymes rather than to the presence of impaired enzymes in the membrane, that only fully competent complexes are present in these membranes, and that iron-deficient complexes are either not assembled or are lost after assembly.

Distinguishing effects of anemia and muscle iron deficiency on exercise bioenergetics in the rat

Three weeks of dietary iron deficiency in weanling rats resulted in anemia (Hb, 3.9 vs. 14.2 g/dl in controls) and decreased oxidative capacities of skeletal muscle (as much as 90% below control values). Whole-animal maximal O2 consumption (VO2max), measured in a brief treadmill run of progressively increasing work load, was approximately 50% lower for iron-deficient rats than for controls, and maximal endurance capacity (time to exhaustion in a separate treadmill run at a constant, sub-Vo2max work load) was 90% lower for iron-deficient rats than for controls. Exchange transfusion, with packed erythrocytes or plasma, was used to adjust Hb to an intermediate concentration of approximately 9.5 g/dl in both iron-deficient and and control rats. This procedure corrected the Vo2max of iron-deficient rats to within 15% of control values, whereas endurance capacity showed no improvement. Our experimental dissociation of Vo2max and endurance capacity provides further evidence that Vo2max is not the sole determinant of endurance. We propose that defects in Vo2max during iron deficiency result primarily from diminished O2 delivery, whereas decreased endurance capacity reflects impaired muscle mitochondrial function.

Diagnosis of anemia and iron deficiency: analytic and biological variations of laboratory tests

We describe the magnitude of analytic errors and the within-subject biological variations for laboratory tests that are used in the diagnosis of anemia and iron deficiency. For Hb, hematocrit, and red cell indices, coefficients of variation for analytic and biological variations are less than 4%. In general, higher coefficients of variation are characteristic of serum iron, iron-binding capacity, serum ferritin, and erythrocyte protoporphyrin. Particularly high analytic variations between different laboratories have been described for iron-binding capacity and the greatest biological variations have been noted for serum iron. An awareness of these sources of error is helpful in designing studies and in interpreting laboratory results.