Recently, data from the American National Health and Nutrition Examination Survey III as well as data obtained in children from transition countries (Morocco and India) have suggested that among children, the prevalence of iron deficiency increases as BMI increases from normal weight to at risk for obesity to obesity [20
]. It remains unclear, however, if the lower serum iron and elevated ferritin seen in obesity are most reflective of a functional iron deficiency related to an inflammatory state, or if obesity is also a risk factor for true iron deficiency [24
At the beginning of our study, obese children with IDA had significantly higher serum ferritin levels than non-obese children with IDA (p < 0.01), and were similar to ferritin levels in healthy children (P > 0.05).
Obesity is considered a chronic inflammatory state [25
]. Serum ferritin concentrations, which are usually suppressed when body iron stores are low [26
], tend to be high and inversely related to transferrin saturation in those with excessive adiposity. Ferritin is considered an acute-phase reactant [24
], hence, it may be elevated in inflammatory conditions even in the presence of true iron deficiency [26
]. cytokines such as interleukin-1β and tumor necrosis factor-α (TNF-α) induce ferritin production within macrophages, hepatocytes and adipocytes [27
In our study, obese children with IDA had significantly higher serum hepcidin levels (p < 0.01), in comparison to non-obese children with IDA and healthy control group (P < 0.01), in contrast, non-obese children with IDA had significantly lower serum hepcidin levels, compared to obese children with IDA and healthy control children (P < 0.01).
Hepcidin is a small peptide hormone secreted by the liver and by adipocytes [9
]. Hepcidin is suppressed in iron deficiency, allowing increased absorption of dietary iron and replenishment of iron stores [28
]. The feedback loop between iron and hepcidin ensures stability of plasma iron concentrations[29
]. Hepcidin is an acute-phase reactant [10
], and its expression is increased in chronic inflammatory states[30
] including obesity [9
]. Hepcidin can inhibit enterocyte iron absorption [31
] and has further been shown to inhibit the release of non-heme iron from macrophages [32
]. Because each of these actions diminishes the amount of bioavailable body iron, it has been suggested that when hepcidin is induced by inflammation, hepcidin is a key iron regulator that causes the hypoferremia and anemia of chronic disease [33
In our study, CRP was significantly higher in obese children with IDA than in non-obese children with IDA and healthy control group (P < 0.05, respectively). Meanwhile, there was no significant difference between non-obese children with IDA and control group as regard CRP (p > 0.05). Yanoff et al [24
] found that CRP concentrations were higher in obese subjects and were positively correlated with BMI, findings consistent with the observation that obesity is an inflammatory state that increases acute-phase reactants.
In our study, treatment of IDA by oral iron therapy for three months was associated with significant improvement of Hb, serum iron and TIBC in cases of IDA (p < 0.05), that was significantly more evident in non-obese children than obese children (P < 0.05).
Zimmermann et al [22
] stated that adiposity in young women predicted not only lower iron absorption but also reduced response to iron supplementation, possibly due to increased hepcidin production.
In our study, serum ferritin increased significantly in non-obese children with IDA after 3 months of oral iron therapy (P < 0.01). On the other hand, obese children with IDA showed non-significant change in serum ferritin before and after oral iron therapy (P > 0.05).
In this study, serum hepcidin increased significantly in non-obese children with IDA after 3 months of oral iron therapy (P < 0.01) and reached to normal value in comparison to healthy control children (Figure ). On the other hand, there was non-significant change in serum hepcidin after oral iron therapy in obese children (P > 0.01).
The regulation of hepcidin in adipose tissue remains unknown and may be similar to other adipokines in subcutaneous and epicardial adipose tissues. Inflammation-induced hepcidin stimulation is mediated through IL-6/STAT3 (signal transducer and activator of transcription-3) pathway [17
]. On the other hand, mRNA for hemojuvelin; a surface molecule important for iron sensing and hepcidin production in the liver [34
]; was not detected in adipose tissue. Hepcidin expression in adipose tissue is thus stimulated rather by inflammatory stimuli than by iron [35
Bariatric surgery resulting in significant and long-lasting weight loss reduces inflammation and consequently, improves iron status in morbidly obese patients [36
In the present study, serum hepcidin in non-obese children with IDA, showed significant positive correlation with Hb, serum iron and transferrin saturation (P < 0.01). In contrast, in obese children with IDA, serum hepcidin showed significant negative correlation with Hb, serum iron and transferrin saturation (P < 0.05).
Although liver hepcidin expression is positively
associated with transferrin saturation, adipocyte hepcidin expression has a positive correlation with BMI, with a trend toward a negative
association with transferrin saturation [9
]. Therefore, lower bioavailability of iron among obese adults might be potentially related to the greater adipose hepcidin. Although hepcidin expression is more than 100-fold higher in hepatocytes than in adipocytes, secreted hepcidin from both tissues may have relevance for humans because in obesity, adipose tissue mass may be 20-fold greater than liver mass [24
It is possible that the proinflammatory cytokines induced by the obese state increase hepcidin expression and upregulate ferritin synthesis in the reticuloendothelial cells [27
] resulting in diminished absorption of iron in the setting of increased storage of iron, whether within the reticuloendothelial system or within adipocytes. Clinically, one would expect this to result in a combination of nutritional iron deficiency and functional iron deficiency [24
]. The limitations of our study included inability to follow our studied obese children for a longer time to detect the possibility of delayed response to iron therapy and whether the reduction of weight will modify our results but that was due to lack of cooperation from the patients and their parents.
Finally, we can conclude that obesity increased hepcidin levels and was associated with diminished response to oral iron therapy in childhood iron deficiency anemia. Further studies in larger groups will be required to verify these findings and to assess the value of weight reduction in refractory IDA of obese children.