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25 Sep 2024 — Iron deficiency affects many US adults even without anemia, heart failure, chronic kidney disease or current pregnancy, according to a nationally representative survey of 8,021 US adults. The researchers call for further studies to determine the optimal absolute screening strategy, as current screening recommendations “may miss 70% of iron deficiency cases among children and during pregnancy.”
Iron deficiency is associated with restless leg syndrome, decreased physical capacity, impaired neurocognitive function, heart failure, all-cause mortality and other adverse outcomes independent of anemia.
The researchers estimate that 14% of the sample is affected by absolute iron deficiency — severely reduced or absent iron stores — and 15% of adults have functional iron deficiency, with adequate iron stores but insufficient availability.
They explain that the Centers for Disease Control and Prevention guidelines on screening and prevention focus on high-risk groups and lack “clear recommendations for iron deficiency surveillance in the general population.”
“Further research on the role of functional iron deficiency in adverse health outcomes and on iron deficiency screening strategies is needed,” they conclude.
Study setup
The study, published in JAMA Network Open, includes data from 8,021 adult participants in the National Health and Nutritional Examination Survey from 2017 to 2020. All participants were noninstitutionalized, civilian women and men aged 18 years or older with available data on serum ferritin, iron and unsaturated iron binding capacity.
Although prior studies indicate that iron deficiency affects a large proportion of children and younger women, the researchers note that its prevalence, especially functional iron deficiency, outside of these groups in the US was unknown.
The team defined absolute iron deficiency as having a serum ferritin — a protein that stores iron in cells — of less than 30 ng/mL regardless of an individual’s transferrin saturation, the ratio of serum iron concentration and the total iron binding capacity and serum iron.
Functional iron deficiency was defined as having a serum ferritin of at least 30 ng/mL but a transferrin saturation of less than 20%.
Only 33% of adults with absolute and 14% with functional iron deficiency had a potential indication for iron deficiency screening.Iron deficiency status
Only an estimated 33% of adults with absolute iron deficiency and 14% with functional iron deficiency had a “potential indication for iron deficiency screening,” including prevalent anemia, heart failure, chronic kidney disease or current pregnancy.
Among US adults without anemia, heart failure, chronic kidney disease or current pregnancy, the estimated prevalence of absolute iron deficiency was 11%, and the prevalence of functional iron deficiency was 15%.
Absolute iron deficiency among women was the highest in participants aged 18–50, while in men, these rates were higher in people over 65. A recent study found that iron deficiency in Swedish military women doubled during training (25% to 55%), while male conscripts only experienced a 3% increase.
“Higher body mass index (BMI) was associated with higher serum ferritin levels. Individuals with anemia, heart failure, chronic kidney disease or current pregnancy were more likely to have absolute, but not functional, iron deficiency than those without such conditions,” the researchers detail.
They note that higher BMI may explain the high prevalence of functional iron deficiency, which is influenced by obesity-related inflammation. The team calls for further study on this relationship.
In addition, the researchers explain that absolute and functional iron deficiency management differs. In absolute iron deficiency, the main goal is to replete iron levels. However, functional iron deficiency is often the result of an inflammatory comorbidity, thus requiring the identification of this underlying cause and treatment. Moreover, healthcare professionals need to determine if an individual also has absolute iron deficiency.
Supplement use
According to the researchers, blood biomarkers, dietary interventions and iron supplements are widely available to manage iron deficiency. However, iron supplement use among affected adults remains infrequent. In the study, iron supplement use ranged from 22% to 35% in women with iron deficiency and 12% to 18% in men, depending on age.
The researchers conclude: “Dietary iron intake, alcohol use and food security were not associated with absolute or functional iron deficiency.”
The use of iron supplements was infrequent among US adults with iron deficiency.However, they also found that estimated dietary iron intake was “significantly lower among women younger than 50 years or 50 years and older compared with men younger than 50 years in fully adjusted models.”
At the same time, the team concedes that it did not account for factors that may influence dietary iron absorption, such as dietary vitamin C content. Adding vitamin C to iron supplements helps iron absorption.
Moreover, they point to other study limitations, such as the small sample, a lack of data on iron deficiency causes and a lack of repeated ferritin and transferrin saturation levels, which meant that the team could not determine trends over time.
Product innovations
The nutrition industry offers several innovations in iron supplementation that help increase absorption or tackle side effects associated with iron supplements, such as a metallic aftertaste or digestive issues.
For example, TopGum created iron-rich gummies with a pleasing flavor and smooth texture. In contrast, Lubrizol Life Science created Lipofer microcapsules with microencapsulated iron to enhance absorption and reduce gastric irritation.
Moreover, research confirms lactoferrin is as effective as iron treatment in patients with low hemoglobin concentration. Although iron supplementation is the most common treatment for these patients, its adverse side effects lead to poor patient adherence.
A multi-partner European consortium has received almost €10 million (US$11.2 million) to research micronutrient deficiencies. The Zero Hidden Hunger EU project will specifically look at iron and zinc deficiencies and assess how much bioavailable iron and zinc people can obtain from their diets.
By Jolanda van Hal