Iron Deficiency: How to Improve Its Absorption.

Iron deficiency in patients with chronic inflammatory diseases is frequent and often underdiagnosed. Without counting the large number of people with iron deficiency anemia, patients with chronic inflammatory diseases such as cancer, heart failure, chronic kidney disease, and inflammatory bowel disease are among the populations with a strong possibility of presenting laboratory levels below recommended. In these patients, the prevalence of iron deficiency has been reported to be as high as 60-90%.

However, ferritin and transferrin saturation, among other more sensitive markers for evaluating iron (Fe), also need attention in populations considered "healthy." Suboptimal Fe levels already reduce physical and mental energy production and metabolic processes, systematically overloading the body, including thyroid function, autoimmunity, and even bone metabolism. From this perspective, sports practitioners and athletes may experience considerable iron loss through inflammation, sweat, urine, and possible hemolysis. Low iron levels can be common in patients with vegetarian or vegan diets, particularly in women.

Given the persistent global situation of low iron levels (versus excess) in various populations, one of the issues currently discussed is about strategies for its better absorption.

Knowledge about the absorption of dietary Fe and the factors (dietary, environmental, lifestyle, genetic) that influence this absorption is growing. From the dietary angle, its absorption is determined by the state and content of heme and non-heme Fe, and the bioavailability of both types, which in turn is determined by the balance between dietary factors that increase or inhibit the absorption of the mineral.

Among the various dietary compounds that can inhibit Fe absorption are phytates, found in many grains and vegetables; calcium, present in dairy foods, eggs, and certain polyphenols like tannins, found in green tea, wines, fruits, and chocolates. Besides containing tannins, certain vegetables like coffee and blueberries contain chlorogenic acid, another mineral inhibitor. Similar to calcium, zinc, manganese, and cobalt can also compete with iron in the body.

Conversely, vitamin C (ascorbic acid), citric acids, and molecules derived from animal tissues are known to aid in Fe absorption, which predominantly occurs in the small intestine.

More recently, we have observed an increase in studies showing the importance of the gut microbiota for iron, especially through increased consumption of prebiotics.

The gut microbiota plays an important role in host nutritional, physiological, and immunological functions, such as food digestion, nutrient absorption, vitamin production, protection of intestinal integrity, immune regulation, and disease pathogenesis.

Part of this valuable contribution comes from the metabolization of prebiotic substances by resident bacteria, leading to the production of short-chain fatty acids (SCFAs), among other metabolites known as postbiotics, such as butyrate and propionate, which facilitate Fe2+ absorption in the intestine.

The best-known prebiotics are inulin, fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), and, more recently, human milk oligosaccharides (HMO).

Ahmad et al. (2021) concluded that inulin and GOS increase SCFA production, thereby increasing Fe absorption in the duodenum and proximal colon.

Husmann et al.'s (2022) review found consistent results for prebiotics FOS and GOS combined with the iron compound ferrous fumarate, from studies in adult women with low Fe stores and anemic infants.

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