Iron

Trivalent plant iron is significantly less absorbed by the human body compared to divalent iron of animal origin. Let's break this down further.

Forms of Iron

• Fe²⁺ (divalent iron) — easily absorbed by the body. Found in heme iron (meat, fish).
• Fe³⁺ (trivalent iron) — an unabsorbable form for humans in isolated form. Found in plant foods (spinach, legumes, grains, etc.).

For Fe³⁺ to become bioavailable, it must be reduced to Fe²⁺ — a process influenced by stomach acidity and the presence of reducers (e.g., vitamin C).

Why is Fe³⁺ not effectively absorbed?

1. Requires reduction to Fe²⁺, with gastric acid (HCl) participating. In cases of reduced acidity (hypoacidity), this process is disrupted. Also, in older age or when taking PPIs (proton pump inhibitors), reduction is practically impossible.
2. Trivalent iron easily binds with phytates, tannins, fiber, forming insoluble complexes. These complexes do not break down in the gastrointestinal tract and cannot be absorbed.

What happens to unabsorbed iron?

When iron is not absorbed in the small intestine, it:

1. Reaches the lower parts of the intestine, including the small and large intestines.
2. Serves as a nutrient medium for pathogenic and conditionally pathogenic microflora.
3. Provokes bacterial imbalance.

SIBO (Small Intestinal Bacterial Overgrowth) is a condition where the microflora, usually residing in the large intestine, excessively proliferates in the small intestine.

There can be many causes for SIBO, but unabsorbed iron is one of the key provocateurs. Because:

• Iron is a primary limiting factor for bacterial growth.
• When there is an excess of iron in the intestinal lumen, it stimulates the growth of bacteria, including conditionally pathogenic ones.
• This disrupts normal digestion, fermentation, causes bloating, diarrhea, flatulence, and malabsorption syndrome.

How to avoid this:

• Use divalent iron from animal sources (liver, meat, eggs).
• Take vitamin C along with plant sources of iron to increase absorption.
• Ensure that stomach acidity is normal.
• Do not abuse iron-containing supplements without indications.
• In case of signs of SIBO — first eliminate bacterial imbalance, and only then prescribe iron.

Biochemical Competition: Iron vs. Zinc

Iron and zinc — are trace elements that are absorbed in the small intestine using similar transport proteins. Primarily through the DMT1 transporter (divalent metal transporter 1). This protein transports divalent metal ions, particularly Fe²⁺ (iron) and Zn²⁺ (zinc).

When there is an excess of iron in the intestine, especially in the form of supplements (e.g., ferrous sulfate, ferrum lactate, etc.), it competes for this transporter, thereby reducing the amount of zinc that can be effectively absorbed. This is called antagonism at the absorption level.

Unbound Iron is Particularly Toxic

When iron enters the body in excessive amounts and in free form (not bound to transport proteins like transferrin), it becomes a pro-oxidative factor — participating in Fenton reactions, creating free radicals (e.g., •OH). This causes damage to the cells of the gastrointestinal tract, further impairing the absorption of other nutrients, including zinc.

Long-term Consequences of Zinc Deficiency

If a person regularly takes iron without considering the antagonism with zinc, it can lead to chronic zinc deficiency, which manifests as:

• weakened immunity (zinc — is critically important for T-cells),
• slowed wound healing,
• deterioration of skin, hair, nails,
• loss of smell and taste,
• hormonal disruptions (zinc is needed for testosterone synthesis),
• intestinal dysfunction (zinc supports the mucosa).

Proportions and Forms of Supplements

To minimize antagonism:

• iron and zinc supplements should be taken at different times of the day, preferably with an interval of 4–6 hours;
• organic forms of zinc (picolinate, citrate, bisglycinate) that have better bioavailability are preferred;
• iron should only be taken when indicated and in bound form (e.g., as part of heme or in complexes with amino acids), rather than in high-dose salts.

Conclusion

When prescribing iron (including in cases of anemia), it is essential to consider the balance with other trace elements, especially zinc, to avoid a chain of new deficiencies.