Hyperinsulinemia may boost both hematocrit and iron absorption by up-regulating activity of hypoxia-inducible factor-1α

Associations of complete blood count parameters with pancreatic beta-cell function and insulin resistance in prediabetes and type 2 diabetes mellitus

INTRODUCTION

Previous studies found controversial associations of CBC parameters with pancreatic beta-cell function (BCF) and insulin resistance (IR). The aim of this was to determine the independent associations of CBC parameters with BCF and IR in prediabetes and type 2 diabetes mellitus (T2DM).

METHODS

This study selected subjects who underwent health checkups at 16 health-promotion centers in 13 Korean cities during 2021. The subjects comprised 1470 patients with normoglycemia, 1124 with prediabetes, and 396 with T2DM. BCF and IR were assessed using the homeostasis model assessment (HOMA)-β and HOMA-IR, respectively. Correlation and multiple linear regression analyses were used to determine the correlation between CBC parameters and HOMA.

RESULTS

While HOMA-IR gradually increased according to red blood cell count quartiles (1.22, 1.40, 1.47, and 1.91, in the first, second, third, and fourth quartiles, respectively; p < 0.001), there was no correlation after adjusting for waist circumference (WC) and HbA1c. The red blood cell distribution width (RDW) was associated with HOMA-β [coefficient (β) = 15.527, p = 0.002], but not with HOMA-IR. White blood cells (WBCs) were associated with HOMA-IR and HOMA-β, which was stronger in HOMA-β (β = 0.505 vs 15.171, p = 0.002) after adjusting for WC and HbA1c. The platelet count was correlated with HOMA-IR and HOMA-β, which only remained in HOMA-β (β = 15.581, p = 0.002) after adjusting for WC and HbA1c.

CONCLUSION

RDW, WBC, and platelet counts were independently associated with only HOMA-β in prediabetes and T2DM. This suggests that these CBC parameters could represent BCF in prediabetes and T2DM.

Pharmacotherapeutic management of comorbid polycystic ovary syndrome and diabetes

INTRODUCTION

Polycystic ovary syndrome (PCOS) is a common endocrine disorder in premenopausal women. Insulin resistance and glucose intolerance are very prevalent metabolic complications in women with PCOS, especially in those presenting with weight excess. Therapeutic strategies targeting insulin resistance in PCOS are of interest because of their overall safety and their beneficial effects on metabolic and reproductive features.

AREAS COVERED

The authors review systematically all of the available therapeutic interventions targeting insulin resistance and/or disturbances of glucose metabolism in women with PCOS.

EXPERT OPINION

The diagnosis of glucose tolerance disorders in women with PCOS requires an oral glucose tolerance test. Strategies addressing weight excess and abdominal adiposity, from lifestyle modification to insulin sensitizers, may improve insulin resistance and glucose tolerance in women with PCOS. However, amelioration of signs and symptoms of PCOS usually requires the loss of large amounts of weight for it to be noticeable. Bariatric surgery has emerged as the most successful approach for obese patients with PCOS, because glucose intolerance, diabetes, and PCOS resolve in most cases through follow-ups. At present, the role of novel drugs targeting insulin resistance and/or diabetes such as inositols, berberine, resveratrol, and incretin-based therapies are yet to be properly established.

Transferrin Saturation: A Body Iron Biomarker

Iron is an essential element for several metabolic pathways and physiological processes. The maintenance of iron homeostasis within the human body requires a dynamic and highly sophisticated interplay of several proteins, as states of iron deficiency or excess are both potentially deleterious to health. Among these is plasma transferrin, which is central to iron metabolism not only through iron transport between body tissues in a soluble nontoxic form but also through its protective scavenger role in sequestering free toxic iron. The transferrin saturation (TSAT), an index that takes into account both plasma iron and its main transport protein, is considered an important biochemical marker of body iron status. Its increasing use in many health systems is due to the increased availability of measurement methods, such as calorimetry, turbidimetry, nephelometry, and immunochemistry to estimate its value. However, despite its frequent use in clinical practice to detect states of iron deficiency or iron overload, careful attention should be paid to the inherent limitations of the test especially in certain settings such as inflammation in order to avoid misinterpretation and erroneous conclusions. Beyond its usual clinical use, an emerging body of evidence has linked TSAT levels to major clinical outcomes such as cardiovascular mortality. This has the potential to extend the utility of TSAT index to risk stratification and prognostication. However, most of the current evidence is mainly driven by observational studies where the risk of residual confounding cannot be fully eliminated. Indeed, future efforts are required to fully explore this capability in well-designed clinical trials or prospective large-scale cohorts.

Iron Status and Metabolic Syndrome in Patients with Non-Alcoholic Fatty Liver Disease

BACKGROUND

A hypothesis has been presented about the role of serum iron, ferritin and transferrin saturation among patients with non-alcoholic fatty liver disease (NAFLD) and resistance to insulin (metabolic syndrome [MetS]), but there is much controversy. This study aimed at investigating the level of serum iron and demographic characteristics in patients with NAFLD with or without MetS.

METHODS

A case-control study was conducted on patients with elevated liver enzymes referring to Baqiyatallah clinic, Tehran, Iran during 2010-2011. After ruling out other causes of increased aminotransferases and approving the diagnosis of NAFLD, the patients were divided into two groups of with or without MetS. Then, the individuals’ demographic, sonographic, and laboratory characteristics were recorded.

RESULTS

This research included 299 patients suffering from NAFLD who were divided into MetS (n=143; 47.8%) and non-MetS (n=156; 52.2%) groups. The age, systolic and diastolic blood pressure, body mass index, waist/hip ratio, glucose tolerance test, serum insulin, C. peptide, triglyceride, and HB A1c were different between MetS and non-MetS groups (p<0.05). There was no significant difference in serum iron and ferritin levels between the two groups, however, a significant correlation was found between serum ferritin and alanine transaminase (p=0.005) and also aspartate aminotransferase (p=0.032).

CONCLUSION

Our findings did not show a significant relationship between iron, in free or storage form, and the presence of MetS among patients with NAFLD, but serum ferritin can correlate with hepatocytes injuries indicated by raised aminotransferases. Nevertheless, to clarify this relationship further molecular, genomic, and histopathological studies are required.

A question mark on iron deficiency in 185 million people of Pakistan: its outcomes and prevention

Micronutrient deficiency especially the iron deficiency is the bane of our lives, affecting all strata of society. Unfortunately, the women during pregnancy, adolescence, and children are under this curse particularly in developing countries like Pakistan. It is one of the biggest reasons of complications during pregnancy and malnourished children under five years of age. Maternal death, still-births, and underweight births are most common consequences of iron deficiency and these outbreaks as iron-deficiency anemia in Pakistan. Disastrous nature of iron deficiency requires an urgent call to eradicate it. Hence, the solution should not be frail comparing with the huge economic loss and other incompatibilities. Flour fortification, supplementation, dietary diversification, and especially maternal education are possible solutions for combating this micronutrient deficiency.

Anaemia, a common but often unrecognized risk in diabetic patients: a review

Anaemia in patients with diabetes, both type 1 and type 2, is a frequent clinical finding. The mechanisms of anaemia are multifactorial and often not very well understood. Iatrogenic causes, including oral antidiabetic drugs, ACE inhibitors and ARBs, and renal insufficiency are the major causes of anaemia in patients with type 2 diabetes. In patients with type 1, the cause is often an associated autoimmune disease, and screening for autoimmune gastritis, pernicious anaemia, Hashimoto's thyroiditis, coeliac disease and Addison's disease is recommended. Other rare causes - including G6PD deficiency, microangiopathic haemolytic anaemia and thiamine-responsive megaloblastic anaemia - should be suspected in young patients or when the classical causes are excluded. Early detection and recognition of the cause(s) of anaemia in patients with diabetes could help to prevent other clinical manifestations as well as the complications of diabetes.

Increased serum ferritin concentrations and liver enzyme activities in patients with metabolic syndrome

Emerging scientific evidence suggests that increases in body iron represent a risk factor for the development of metabolic syndrome and diabetes. The aim of our study was to determine the body iron stores in patients with metabolic syndrome, and to evaluate the potential relationship of iron overload with specific features of the metabolic syndrome, such as fatty liver. A total of 490 individuals were enrolled. The diagnosis of metabolic syndrome was based on National Cholesterol Education Program-Adult Treatment Panel III (ATPIII) criteria. The metabolic syndrome group was consisted of 185 patients having three or more criteria, whereas individuals with less than three criteria constituted the control group. Metabolic syndrome patients displayed higher ferritin concentration as compared to control individuals. Ferritin levels were positively correlated with insulin concentration, as well as with Homeostasis Model Assessment (HOMA) index values. Multiple regression analysis revealed that ferritin was the most important independent determinant of insulin resistance indices. Patients with metabolic syndrome also exhibited increased concentrations of alanine aminotransferase and gamma-glutamyltranspeptidase compared to controls. Multiple regression analysis revealed that ferritin concentration was the most important determinant of gamma-glutamyltranspeptidase levels. Patients with the metabolic syndrome exhibit an increase in body iron stores as well as elevated concentrations of liver enzymes compared to the individuals who do not fulfill the criteria for the diagnosis of this syndrome. Our data support a direct role of increased body iron in the pathogenesis of insulin resistance, whereas iron overload may also contribute to the development of specific features of the metabolic syndrome, such as fatty liver.

Association of serum ferritin with metabolic syndrome and diabetes mellitus in the South Korean general population according to the Korean National Health and Nutrition Examination Survey 2008

We examined the association of serum ferritin levels with metabolic syndrome (MS) and diabetes mellitus in a representative sample of the adult South Korean population using data from the 2008 Korean National Health and Nutrition Examination Survey. We conducted a cross-sectional study of 6311 adults older than 20 years who participated in the 2008 Korean National Health and Nutrition Examination Survey. Metabolic syndrome was defined as the presence of at least 3 of the following: elevated blood pressure, low high-density lipoprotein cholesterol, elevated serum triglycerides, elevated plasma glucose, and abdominal obesity. Diabetes mellitus was defined as fasting glucose of at least 126 mg/dL. Insulin resistance was determined using the homeostasis model assessment estimate of insulin resistance. In a representative sample of the adult Korean population, MS was more prevalent in the highest quartile compared with the lowest quartile of serum ferritin concentrations in women following adjustments for age, education, smoking, alcohol intake, body mass index, aspartate aminotransferase, and alanine aminotransferase. Diabetes mellitus was more prevalent in the highest quartile compared with the lowest quartile of serum ferritin concentrations in premenopausal women and men. The geometric means of fasting insulin and insulin resistance determined using the homeostasis model assessment of insulin resistance in the fourth serum ferritin quartiles of postmenopausal women and men were significantly higher compared with those in the first quartile of the respective groups. The present study demonstrates that elevated serum ferritin concentrations are associated with an increased risk of MS and diabetes mellitus in a representative sample of the adult South Korean population.

Early interplay of intra-hepatic iron and insulin resistance in children with non-alcoholic fatty liver disease

BACKGROUND & AIMS

The liver is a crucial organ at the crossroads of iron and glucose metabolism. The aim of the study was to assess intra-hepatic iron in young patients with non-alcoholic fatty liver disease (NAFLD) and its association with insulin resistance and severity of liver damage.

METHODS

Intrahepatic iron content was assessed (Pearl's stain grade) in 66 patients (41 males, age 3.3-17.6years) with biopsy-proven NAFLD. Mutations of the Hereditary Hemochromatosis (HFE) gene were determined by sequence allele-specific polymerase chain reaction. Insulin resistance was estimated by means of the Oral Glucose Tolerance Test and the Insulin Sensitivity Index (ISI); the Insulino-Genic Index was also calculated. Tumor necrosis factor-alpha and interleukin-6 were measured.

RESULTS

Low-mild intra-hepatic iron deposition was observed in one out of five children (n=15, 22%), and it was not associated with HFE mutations, carried by 17 patients (26%). Among carriers of HFE mutations, four had siderosis. No abnormalities were observed in systemic indices of iron balance. Serum ferritin was within normal adult ranges in all patients (33.6±7.6ng/ml), but it was correlated with ISI (r(o)=-0.361; p=0.003). No significant difference was observed in insulin sensitivity, iron balance, inflammatory milieu, and liver histology between patients with and without hepatic siderosis.

CONCLUSIONS

In young obese individuals with NAFLD, despite normal peripheral iron parameters, mild intra-hepatic iron deposition is a frequent finding, but it is not associated with insulin resistance or severity of liver damage. Longitudinal studies are required to define the long-term relevance of these findings.

Effect of metformin on serum ferritin level in women with polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is one of the most common diseases among women associat-ed with various inflammatory reactants such as C-reactive protein (CRP) and ferritin. This study aimed to investi-gate the effect of metformin on probable reduction of serum ferritin in patients with PCOS.

METHODS

This study was conducted on 45 patients with PCOS who had not other systemic diseases and did not take any medications. Weight, waist and hip circumstances (WHR), body mass index (BMI), metabolic indexes, CRP, ferritin and "Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) ˝ were measured before the study. Metformin (500 mg/tid) tablets were prescribed for three months and then same above parameters were re-measured.

RESULTS

Of 45 patients, 19 (42.2%) were overweight and 14 (31.1%) were obese. After drug therapy, there was a significant reduction in waist circumstance and serum ferritin. This reduction was significant only in the lean and overweight groups but not in the obese group. There was not significant association between serum ferritin and CRP, HOMA-IR, BMI and WHR. There was not significant correlation between CRP and HOMA-IR and also BMI.

CONCLUSION

The effect of metformin on reduction of serum ferritin was not significant just in obese group and was not associated with metabolic and anthropometric indexes.

Role of decreased circulating hepcidin concentrations in the iron excess of women with the polycystic ovary syndrome

CONTEXT

Hepcidin inhibits the intestinal absorption of iron and its deficiency causes juvenile hemochromatosis.

OBJECTIVE

The objective of the investigation was to study the involvement of hepcidin in the iron overload of patients with polycystic ovary syndrome (PCOS).

DESIGN

This was a case-control study followed by a randomized clinical trial.

SETTING

The study was conducted at an academic hospital.

PATIENTS

Thirty-four patients with PCOS and 30 women without hyperandrogenism, matched for age and body mass index, participated in the study.

INTERVENTION

Patients with PCOS were randomly allocated to treatment with either an antiandrogenic oral contraceptive or metformin for 24 wk.

MAIN OUTCOME MEASURES

Serum hepcidin levels and ferritin to hepcidin molar ratios were measured.

RESULTS

Patients with PCOS showed decreased circulating hepcidin levels and increased ferritin to hepcidin molar ratios compared with controls. Patients with PCOS presenting with chronic oligoamenorrhea (an iron sparing mechanism) showed a paradoxical decrease in serum hepcidin levels and an increase in ferritin to hepcidin molar ratios compared with the patients who had regular anovulatory menstrual cycles and with the controls. The major predictor of circulating hepcidin concentrations was the presence of PCOS, whereas the main determinants of the ferritin to hepcidin molar ratio were the insulin sensitivity index and menstrual dysfunction. Serum hepcidin levels did not change during treatment with either metformin or the antiandrogenic oral contraceptive pill, yet patients treated with the oral contraceptive pill normalized the ferritin to hepcidin molar ratio.

CONCLUSIONS

Patients with PCOS had reduced serum hepcidin concentrations that might contribute to their iron overload by favoring the intestinal absorption of iron. The imbalance between increased iron stores and reduced hepcidin levels was related to the insulin resistance and androgen excess characteristic of this syndrome.

Dietary intake and serum and hair concentrations of minerals and their relationship with serum lipids and glucose levels in hypertensive and obese patients with insulin resistance

Inadequate minerals intake, as well as disruption of some metabolic processes in which microelements are cofactors, are suggested to lead to the development of hypertension. The role of minerals in the pathogenesis of hypertension still remains to be explained. In the present study, we sought to determine associations between serum and hair mineral concentrations and serum lipids and glucose levels. Forty obese hypertensive subjects with insulin resistance and 40 healthy volunteers were recruited in the study. Blood pressure, BMI, and insulin resistance were recorded in all subjects. Levels of lipids, glucose, sodium and potassium, iron, copper, zinc, magnesium, and calcium were assessed in serum. Iron, copper, zinc, magnesium, and calcium were assessed in hair. Dietary intake of the analyzed minerals was estimated. We found distinctly higher concentrations of serum iron and serum and hair calcium as well as markedly lower levels of hair zinc in the hypertensive subjects. The study group manifested also significantly lower daily intake of calcium, magnesium, and iron. We observed a relationship between the concentrations of iron, zinc, and copper in serum and hair and high and low range of cholesterol, triglycerides, and glucose serum levels in the studied patients. Moreover, this study demonstrated significant correlation between serum and hair concentrations of selected minerals and their dietary intake and levels of serum lipids and glucose and blood pressure in the study and the control groups. The obtained results seem to indicate the association between lipid and glucose metabolism and iron, copper, zinc, and calcium concentrations in blood and hair of hypertensive and obese patients with insulin resistance.

Body iron stores and glucose intolerance in premenopausal women: role of hyperandrogenism, insulin resistance, and genomic variants related to inflammation, oxidative stress, and iron metabolism

OBJECTIVE Increased serum ferritin levels and iron stores may be involved in the development of abnormal glucose tolerance in women presenting with obesity and/or polycystic ovary syndrome (PCOS). We aimed to study the determinants of serum ferritin levels in premenopausal women among indexes of insulin resistance, adiposity, hyperandrogenism, and genotypes pertaining to inflammation, oxidative stress, and iron metabolism. RESEARCH DESIGN AND METHODS A total of 257 premenopausal women, classified depending on the presence or absence of PCOS, obesity, and/or abnormal glucose tolerance, underwent a complete metabolic evaluation, serum ferritin, haptoglobin, and C-reactive protein (CRP) measurements, and genotyping for proinflammatory and prooxidant variants and mutations in the HFE gene. RESULTS Serum ferritin concentrations were increased in women presenting with PCOS and/or abnormal glucose tolerance, independent of obesity. A stepwise multivariate linear regression analysis (R(2) = 0.18, P < 0.0001) retained menstrual dysfunction (beta = 0.14, P = 0.035), free testosterone (beta = 0.14, P = 0.052), insulin sensitivity index (beta = -0.12, P = 0.012), the His63Asp variant in HFE (beta = 0.16, P = 0.008), and abnormal glucose tolerance (beta = 0.15, P = 0.015) as significant predictors of the logarithm of ferritin levels, whereas CRP, haptoglobin, waist-to-hip ratio, or variants in the TNFalpha, TNFRSF1B, IL6, IL6ST, IL6Ralpha, PON1, and HFE Cys282Tyr mutation exerted no influence. CONCLUSIONS Androgen excess (partly because of hyperandrogenemia and partly because of menstrual dysfunction), insulin resistance, abnormal glucose tolerance, and the HFE His63Asp variant correlate with ferritin levels in premenopausal women.

Age- and body mass index-dependent relationship between correction of iron deficiency anemia and insulin resistance in non-diabetic premenopausal women

BACKGROUND

No prospective studies have evaluated the effects of correction of iron deficiency anemia on insulin resistance in non-diabetic premenopausal women. We investigated this relationship in 54 non-diabetic premenopausal women with iron deficiency anemia.

SUBJECTS AND METHODS

All patients were treated with oral iron preparations. Insulin resistance was calculated with the Homeostasis Model Assessment formula. All patients were dichotomized by the median for age and BMI to assess how the relationship between iron deficiency anemia and insulin resistance was affected by age and BMI.

RESULTS

Although the fasting glucose levels did not change meaningfully, statistically significant decreases were found in fasting insulin levels following anemia treatment both in the younger age (<40 years) (P=0.040) women and in the low BMI (<27 kg/m2) (P=0.022) subgroups but not in the older age (>or=40 years) and the high BMI (>or=27 kg/m2) subgroups. Post-treatment fasting insulin levels were positively correlated both with BMI (r=0.386, P=0.004) and post-treatment hemoglobin levels (r=0.285, P=0.036). Regression analysis revealed that the factors affecting post-treatment insulin levels were BMI (P=0.001) and post-treatment hemoglobin levels (P=0.030).

CONCLUSION

Our results show that following the correction of iron deficiency anemia, insulin levels and HOMA scores decrease in younger and lean non-diabetic premenopausal women.

Increased body iron stores of obese women with polycystic ovary syndrome are a consequence of insulin resistance and hyperinsulinism and are not a result of reduced menstrual losses

OBJECTIVE

Increased serum ferritin levels, indicating increased body iron stores, have been found in overweight and obese women with polycystic ovary syndrome (PCOS). This finding might result from reduced menstrual losses secondary to oligo- or amenorrhea or from hyperinsulinism secondary to insulin resistance, because insulin favors the intestinal absorption and the tissue deposition of iron. To explore which of these mechanisms is responsible for the increase in body iron stores in women with PCOS, we have monitored the changes in serum ferritin levels during treatment with an antiandrogenic oral contraceptive or an insulin sensitizer.

RESEARCH DESIGN AND METHODS

Thirty-four consecutive PCOS patients were randomized to an oral contraceptive containing 35 microg ethinyl-estradiol plus 2 mg cyproterone acetate (Diane(35) Diario) or metformin (850 mg twice daily), and their serum ferritin levels were evaluated at baseline and after 12 and 24 weeks of treatment.

RESULTS

Despite the fact that treatment with Diane(35) Diario restored regular menstrual cycles in all the patients, whereas metformin only did so in 50% of them, serum ferritin levels decreased at 12 and 24 weeks of treatment only with metformin, in association with a marked increase in insulin sensitivity. On the contrary, no changes in ferritin and insulin sensitivity were observed with Diane(35) Diario.

CONCLUSIONS

Our present results suggest that insulin resistance and hyperinsulinism, and not the reduced menstrual losses secondary to from oligo- or amenorrhea, are responsible of the increased ferritin levels and body iron stores found in overweight and obese women with PCOS.

Endocrine responses to acute and chronic high-altitude exposure (4,300 meters): modulating effects of caloric restriction

High-altitude anorexia leads to a hormonal response pattern modulated by both hypoxia and caloric restriction (CR). The purpose of this study was to compare altitude-induced neuroendocrine changes with or without energy imbalance and to explore how energy sufficiency alters the endocrine acclimatization process. Twenty-six normal-weight, young men were studied for 3 wk. One group [hypocaloric group (HYPO), n = 9] stayed at sea level and consumed 40% fewer calories than required to maintain body weight. Two other groups were deployed to 4,300 meters (Pikes Peak, CO), where one group (ADQ, n = 7) was adequately fed to maintain body weight and the other [deficient group (DEF), n = 10] had calories restricted as above. HYPO experienced a typical CR-induced reduction in many hormones such as insulin, testosterone, and leptin. At altitude, fasting glucose, insulin, and epinephrine exhibited a muted rise in DEF compared with ADQ. Free thyroxine, thyroid-stimulating hormone, and norepinephrine showed similar patterns between the two altitude groups. Morning cortisol initially rose higher in DEF than ADQ at 4,300 meters, but the difference disappeared by day 5. Testosterone increased in both altitude groups acutely but declined over time in DEF only. Adiponectin and leptin did not change significantly from sea level baseline values in either altitude group regardless of energy intake. These data suggest that hypoxia tends to increase blood hormone concentrations, but anorexia suppresses elements of the endocrine response. Such suppression results in the preservation of energy stores but may sacrifice the facilitation of oxygen delivery and the use of oxygen-efficient fuels.

Relation between insulin resistance and hematological parameters in a Brazilian sample

It has already been demonstrated that insulin resistance (IR) is associated with the stimulation of erythroid progenitors and with increased levels of inflammation markers. Therefore, IR should also be associated with increased red blood cell (RBC) and white blood cell (WBC) count. The aim of this study is to demonstrate that IR is independently associated with altered hematological parameters in a Brazilian sample. We analyzed laboratorial exams from 925 subjects. All data on hematological parameters, insulin resistance (Homeostasis Model Assessment [HOMA]) and lipid levels were included in the analysis. Demographic information included age and gender. HOMA correlated positively with RBC (r= 0.17, p< 0.001), plasma hemoglobin concentrations (r= 0.14, p< 0.001), hematocrit value (r= 0.15, p< 0.001) and WBC (r= 0.17, p< 0.01). Subjects in the upper quartile of IR had higher levels of plasma glucose, fasting insulin, triglycerides, hematocrit, hemoglobin, RBC and WBC count than those in the lower quartile. In conclusion, IR seems to be associated with alterations in several hematological parameters. These hematological alterations may be considered an indirect feature of the IR syndrome.

Iron, oxidative stress and human health

The amount of iron within the cell is carefully regulated in order to provide an adequate level of the micronutrient while preventing its accumulation to toxic levels. Iron excess is believed to generate oxidative stress, understood as an increase in the steady state concentration of oxygen radical intermediates. The main aspects of cellular metabolism of iron, with special emphasis on the role of iron with respect to oxidative damage to lipid membranes, are briefly reviewed here. Both in vitro and in vivo models are examined. Finally, a discussion of iron overload and its impact on human health is included. Overall, further studies are required to assess more effective means to limit iron-dependent damage, by minimizing the formation and release of free radicals in tissues when the cellular iron steady state concentration is increased either as a consequence of disease or by therapeutic iron supplementation.

Serum ferritin and risk of the metabolic syndrome in U.S. adults

OBJECTIVE

We examined the relationship among iron stores, the metabolic syndrome, and insulin resistance.

RESEARCH DESIGN AND METHODS

We conducted a cross-sectional study of 6,044 adults >20 years of age who participated in the Third National Health and Nutrition Examination Survey. Metabolic syndrome was defined as the presence of at least three of the following: elevated blood pressure, low HDL cholesterol, elevated serum triglycerides, elevated plasma glucose, and abdominal obesity. Insulin resistance was estimated using homeostasis model assessment (for insulin resistance), fasting insulin, and triglyceride-to-HDL cholesterol ratio.

RESULTS

After excluding individuals with likely hemochromatosis, mean serum ferritin values in premenopausal women, postmenopausal women, and men were 33.6, 93.4, and 139.9 microg/l, respectively. Metabolic syndrome was more common in those with the highest compared with the lowest levels of serum ferritin in premenopausal women (14.9 vs. 6.4%, P = 0.002), postmenopausal women (47.5 vs. 28.2%, P < 0.001), and men (27.3 vs. 13.8%, P < 0.001). Insulin resistance also increased across quartiles of serum ferritin for men and postmenopausal women and persisted after adjustment for age, race/ethnicity, C-reactive protein, smoking, alcohol intake, and BMI.

CONCLUSIONS

Elevated iron stores were positively associated with the prevalence of the metabolic syndrome and with insulin resistance.