Absolute, Functional Iron Deficiency Affects Large Proportion of US Adults

Leo F. Buckley, PharmD

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A new investigation into absolute and functional iron deficiency rates in the United States revealed a large proportion of the population was affected between 2017 and 2020, even without anemia, heart failure (HF), or chronic kidney disease (CKD).¹

These data suggested the considerable risk faced by the general population for absolute and functional iron deficiency, particularly those without known risk factors. Brigham and Women’s Hospital-based investigators indicated these results remained in line with European-based studies showing high rates of absolute iron deficiency in the general population.²

“This cross-sectional study indicates that both absolute and functional iron deficiency affects a large proportion of adults in the US, especially among those without conditions often screened for iron deficiency,” wrote the investigative team, led by Leo F. Buckley, PharmD, department of pharmacy services, Brigham and Women’s Hospital.

Iron deficiency is typically prevented or treated with dietary intervention or non-prescription iron supplementation, but current use in the US has not been studied.³ Estimates are necessary to determine patient populations at risk of iron deficiency-related adverse outcomes, screening recommendations, and priorities for research.

In this analysis, Buckley and colleagues sought to evaluate the presence of absolute and functional iron deficiency, followed by iron supplementation, in the US across sex, age, and comorbidity categories.¹ Data were obtained from the National Health and Nutritional Examination Survey (NHANES) 2017 to 2020 pre-pandemic cycle.

Participants (n = 8021) were non-institutionalized men and women aged ≥18 with available serum ferritin, iron, and unsaturated iron binding capacity measures. Absolute iron deficiency was categorized as a serum ferritin level <30 ng/mL, irrespective of transferrin. Functional iron deficiency was defined as serum ferritin ≥30 ng/mL, with transferrin saturation <20%.

Investigators estimated the prevalence of absolute and functional iron deficiency among all US adults in the analysis, and separately by age category: >18 years to <50 years, 50–65 years, and ≥65 years. Prevalence estimates were based on recommended sample weights and sampling design factors to represent the national, noninstitutionalized civilian population.

Among the study population, approximately 14% (95% CI, 13–15) of US adults met criteria for absolute iron deficiency, and an estimated 15% (95% CI, 14–17) exhibited criteria for functional iron deficiency. For adults without anemia, HF, CKD, or current pregnancy, the estimated prevalence was 11% (95% CI, 10–11) and 15% (95% CI, 14–17) for absolute and functional iron deficiency, respectively.

Both absolute and functional iron deficiency rates were increased for women over men across all age categories. For women, absolute iron deficiency was nearly 34% (95% CI, 31–37) in participants aged 18–50 years, while the prevalence was highest for men aged ≥65 (7%; 95% CI, 5–10). Functional iron deficiency was more common in all age and sex categories, aside from women <50 years.

Dependent on age, the use of iron supplementation varied from 22% (95% CI, 12–37) to 35% (95% CI, 29–42) in women with iron deficiency and from 12% (95% CI, 5–21) to 18% (95% CI, 8–32) of men with iron deficiency. Fully adjusted models showed absolute iron deficiency was linked to an approximately 3-fold higher rate of iron supplement use than iron-replete status (P <.001).

In their conclusion, Buckley and colleagues called for further research into the role of functional iron deficiency in adverse clinical outcomes and screening strategies used to identify iron deficiency. The team noted the importance of understanding the sex- and age-related patterns in these data for management strategies.

“Since the causes, and potentially the treatments, for absolute and functional iron deficiency differ, these age-related and sex-related patterns may have implications for the management of iron deficiency,” they wrote. “...Further research on the role of functional iron deficiency in adverse health outcomes and on iron deficiency screening strategies is needed.”

References

1. _{Tawfik YMK, Billingsley H, Bhatt AS, et al. Absolute and Functional Iron Deficiency in the US, 2017-2020. JAMA Netw Open. 2024;7(9):e2433126. doi:10.1001/jamanetworkopen.2024.33126}
2. _{Philip KEJ, Sadaka AS, Polkey MI, Hopkinson NS, Steptoe A, Fancourt D. The prevalence and associated mortality of non-anaemic iron deficiency in older adults: a 14 years observational cohort study. Br J Haematol. 2020;189(3):566-572. doi:10.1111/bjh.16409}
3. _{Nguyen M, Tadi P. Iron Supplementation. [Updated 2023 Jul 3]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557376/}