Acute functional iron deficiency in obese subjects during a very-low-energy all-protein diet

Iron Deficiency Anemia Prevalence at First Stroke or Transient Ischemic Attack

Background:

Iron deficiency anemia (IDA) has been implicated in the etiology of transient ischemic attack and ischemic stroke. This study aimed to: 1) document IDA prevalence in patients ≥ 65 years of age admitted to hospital with transient ischemic attack or first ischemic stroke, and 2) investigate dietary intake as a predictor of iron status.

Methods:

Ninety-four patients were enrolled. An algorithm containing values for hemoglobin, ferritin, total iron binding capacity, transferrin saturation, and serum transferrin receptor measured at admission was used to identify IDA. Usual dietary intake was assessed with the Clue II food frequency questionnaire.

Results:

Prevalence estimates were 6.4% for IDA, 2.1% for iron deficiency without anemia, and 6.4% for anemia from other causes. IDA prevalence was significantly higher than published National Health and Nutrition Examination Survey III (NHANES III) estimates for gender-specific age groups ≥ 70 years (One-Sample Proportion Test; males p = 0.038 [n= 37]; females p = 0.002 [n=44]). A comparison of IDA prevalence against selected controls from the NHANES III database yielded an odds ratio (OR) of 6.3, 95% confidence interval (CI) 0.8 to 53.7, which was not statistically significant (Fisher's Exact Test; n=94; p = 0.118). Multivariate linear regression analysis of dietary intake with indicators of iron status (n=58) revealed only iron supplements (p = 0.013) and heme iron intake (p = 0.038) as negative predictors of total iron binding capacity (p<0.05).

Conclusions:

These findings support the initiation of a prospective case control study to investigate IDA as a risk factor for ischemic stroke in elderly patients.

Greater prevalence of iron deficiency in overweight and obese children and adolescents

OBJECTIVE

To assess whether overweight children and adolescents, who often have poor dietary habits, are at increased risk of iron deficiency (ID).

METHODS

The study sample included 321 children and adolescents followed in two endocrine centers in Israel between 1999 and 2001. The subjects were divided into three groups on the basis of body mass index (BMI) for age and gender as follows: group 1-BMI below 85th percentile (normal weight); group 2-BMI above 85th, but below 97th percentile (overweight); and group 3-BMI above 97th percentile (obese). ID was defined as iron levels <8 micromol/l (45 mcg/dl), and iron-deficiency anemia (IDA) was defined as ID and hemoglobin level below 2 standard deviation score (SDS) for the mean for age and gender.

RESULTS

Iron levels below 8 micromol/l (45 mcg/dl) were noted in 38.8% of the obese children and 12.1% of the overweight children, compared with 4.4% of the normal-weight group (P<0.001). There was a significant negative correlation of low iron levels with BMI SDS (r=-0.44, P<0.001), but not with age or gender. Among the children with ID, 26.6% also had IDA. Groups 1, 2, and 3 accounted for 6.7%, 35%, and 58.3% of the children with IDA, respectively.

CONCLUSIONS

ID is common in overweight and obese children. A significantly greater proportion of obese than normal-weight children have IDA. Insufficient dietary intake of iron, whether absolute or relative to body mass, and increased iron needs may be a result of unbalanced nutrition or repeated short-term restrictive diets. Because of potentially harmful effects of ID, obese children should be routinely screened and treated as necessary.

Soluble transferrin receptor for the evaluation of erythropoiesis and iron status

Iron transport in the plasma is carried out by transferrin, which donates iron to cells through its interaction with a specific membrane receptor, the transferrin receptor (TfR). A soluble form of the TfR (sTfR) has been identified in animal and human serum. Soluble TfR is a truncated monomer of tissue receptor, lacking its first 100 amino acids, which circulates in the form of a complex of transferrin and its receptor. The erythroblasts rather than reticulocytes are the main source of serum sTfR. Serum sTfR levels average 5.0+/-1.0 mg/l in normal subjects but the various commercial assays give disparate values because of the lack of an international standard. The most important determinant of sTfR levels appears to be marrow erythropoietic activity which can cause variations up to 8 times below and up to 20 times above average normal values. Soluble TfR levels are decreased in situations characterized by diminished erythropoietic activity, and are increased when erythropoiesis is stimulated by hemolysis or ineffective erythropoiesis. Measurements of sTfR are very helpful to investigate the pathophysiology of anemia, quantitatively evaluating the absolute rate of erythropoiesis and the adequacy of marrow proliferative capacity for any given degree of anemia, and to monitor the erythropoietic response to various forms of therapy, in particular allowing to predict response early when changes in hemoglobin are not yet apparent. Iron status also influences sTfR levels, which are considerably elevated in iron deficiency anemia but remain normal in the anemia of inflammation, and thus may be of considerable help in the differential diagnosis of microcytic anemia. This is particularly useful to identify concomitant iron deficiency in a patient with inflammation because ferritin values are then generally normal. Elevated sTfR levels are also the characteristic feature of functional iron deficiency, a situation defined by tissue iron deficiency despite adequate iron stores. The sTfR/ferritin ratio can thus describe iron availability over a wide range of iron stores. With the exception of chronic lymphocytic leukemia (CLL) and high-grade non-Hodgkin's lymphoma and possibly hepatocellular carcinoma, sTfR levels are not increased in patients with malignancies. We conclude that soluble TfR represents a valuable quantitative assay of marrow erythropoietic activity as well as a marker of tissue iron deficiency.

Defining optimal body iron

The major liabilities of Fe lack include defects in psychomotor development in infants, impaired educational performance in schoolchildren, increased perinatal morbidity, and impaired work capacity. Few if any of the relevant investigations have demonstrated these abnormalities in the absence of anaemia. Consequently, adequate Fe nutrition can be defined as a normal haemoglobin concentration. On the other hand, optimal Fe nutrition should be regarded as sufficient body Fe to avoid any limitation in tissue Fe supply, termed Fe-deficient erythropoiesis. A variety of laboratory measurements have been used to identify this milder form of Fe deficiency, including serum ferritin, transferrin saturation, erythrocyte protoporphyrin, mean corpuscular volume, and more recently the concentration of the soluble fragment of transferrin receptor in serum. Recent studies indicate that the serum transferrin receptor is the preferred measurement, because enhanced synthesis of the transferrin receptor represent the initial cellular response to a declining Fe supply. Moreover, unlike other methods, it is not affected by chronic inflammation or infection which are often confused with Fe deficiency. In an otherwise normal healthy population the transferrin receptor: ferritin value provides a useful quantitative index of body Fe over a wide spectrum of Fe status, ranging from Fe repletion to Fe-deficiency anaemia. It is concluded that optimal Fe nutrition is best defined as a normal haemoglobin, serum ferritin and transferrin receptor concentration.

Erythropoietin and iron

Serum ferritin concentration is most informative in estimating the amount of storage iron available for a particular individual. The serum transferrin receptor concentration, in contrast to serum ferritin, provides direct information about any deficit in the adequacy of iron supply to the erythropoiesis. The combination of serum transferrin receptor and serum ferritin provides complete information about storage and functional iron compartments. Using this combination along with the hemoglobin concentration, it is possible to define the iron nutritional status completely. Inflammatory conditions as well as parenteral iron administration interfere, however, with the direct and quantitative ferritin to storage iron relationship and, therefore, have to be considered carefully with respect to diagnostic purposes. The diagnostic use of the serum transferrin receptor is presently limited because of limitations in methodology and definition (standardization) of reference ranges.