Assessment of iron deficiency in the context of the obesity epidemic: importance of correcting serum ferritin concentrations for inflammation.

BACKGROUND

The correction of serum ferritin (SF) concentrations for inflammation because of infectious or parasitic diseases was recently proposed, especially in developing countries, but in many countries, adiposity has become the main cause of inflammation.

OBJECTIVE

We assessed, overall and by adiposity status, the bias in the estimation of iron deficiency (ID) on the basis of uncorrected SF.

DESIGN

A cross-sectional survey in 2010 in Rabat-Salé, Morocco, used a random sample of 811 women aged 20-49 y. Adiposity was assessed by body mass index (BMI) (in kg/m²) (normal: BMI <25; overweight: BMI ≥25 to <30; obese: BMI ≥30), waist circumference, and body fat. Inflammation was indicated by a C-reactive protein (CRP) concentration >2 mg/L. ID was indicated by an SF concentration <15 μg/L. The correction factor of SF for inflammation was derived from our sample. Differential effects of SF correction on ID status on the basis of adiposity were assessed by models that included adiposity × correction interactions and accounted for the within-subject correlation.

RESULTS

The prevalence of overweight was 33.0% and of obesity was 34.0%. Inflammation (42.3%) was strongly linked with adiposity (20.1%, 37.6%, and 68.4% in normal, overweight, and obese subjects, respectively; P < 0.0001). SF increased from a CRP concentration >2 mg/L. The correction factor of SF was 0.65. The prevalence of ID (37.2% compared with 45.2%; difference -8.0%, P < 0.0001) was underestimated by not correcting SF, and the difference increased with adiposity (-2.9%, -8.5%, and -12.4% in normal, overweight, and obese subjects, respectively; P-interaction < 0.0001). Analogous results were observed for other adiposity measures.

CONCLUSION

In developing countries where ID remains prevalent but rates of obesity are already high, corrected SF should be used when assessing ID status, even if infectious or parasitic diseases are no longer widespread. This trial was registered at clinicaltrials.gov as NCT01844349.