Iron – The Transport Mineral for Energy and Oxygen

Iron is one of the most common minerals in the human body and is indispensable for the formation of hemoglobin, the red blood pigment. Without sufficient iron, your body cannot effectively transport oxygen – with direct consequences for endurance, concentration, and the immune system.

What is Iron and How Does it Work?

Iron is an essential trace element that exists in two forms: heme iron (animal-derived) and non-heme iron (plant-derived). In the body, iron performs central functions:

Hemoglobin Synthesis: ~70% of the body's iron is bound in hemoglobin, which transports oxygen from the lungs to the tissues.
Myoglobin: Stores oxygen in the muscles for short-term availability.
Enzyme Functions: Iron is a cofactor for over 100 enzymes, including those involved in energy production (cytochromes of the respiratory chain).
DNA Synthesis: Necessary for ribonucleotide reductase, the key enzyme in DNA replication.

Iron Deficiency – The Most Common Nutrient Deficiency Worldwide

The WHO estimates that over 2 billion people suffer from iron deficiency. Symptoms develop gradually:

Pale skin, brittle nails, hair loss
Chronic fatigue, shortness of breath during exertion
Concentration problems, irritability
Restless Legs Syndrome
Increased susceptibility to infections

Bioavailability: Heme vs. Non-Heme Iron

Iron Form	Source	Bioavailability	Influencing Factors
Heme iron (Fe2+)	Meat, fish, liver	15–35 %	Hardly affected
Non-heme iron (Fe3+)	Legumes, grains, spinach	2–15 %	Highly variable

Absorption Promoters

Vitamin C (Ascorbic acid): Reduces Fe3+ to bioavailable Fe2+, increases absorption up to 6-fold
Meat factor (heme iron): Simultaneously promotes non-heme absorption
Fermented foods: Reduce phytates

Absorption Inhibitors

Phytates (whole grains, legumes): Form insoluble iron-phytate complexes
Calcium: Competitive antagonist at the transport site
Tannins (tea, coffee, red wine): Bind iron in the intestine
Oxalates (spinach, rhubarb): Form poorly soluble compounds

Dosage Recommendations

Group	Daily Requirement (DGE)	Special Considerations
Men (19–50 y.)	10 mg/day	Losses through sweat during exercise
Women (19–50 y.)	15 mg/day	Consider menstrual losses
Pregnant women	27 mg/day	Increased need for fetal development
Breastfeeding women	20 mg/day	–
Vegetarians/Vegans	1.8× higher	Account for lower bioavailability
Endurance athletes	+30–70 %	"Foot-strike hemolysis", sweat

Iron Stores in the Body

The body regulates iron absorption via the hormone hepcidin: When stores are full, hepcidin is released and blocks absorption. In case of deficiency, hepcidin decreases, and intestinal cells open their iron transporters (ferroportin). Ferritin is the most important iron storage protein – serum ferritin levels are the most sensitive marker for overall body iron status.

Testing Iron Status – Which Lab Values Matter?

Parameter	Normal Range	Significance
Serum ferritin	12–150 µg/l (women) / 12–300 µg/l (men)	Iron stores (most sensitive marker)
Serum iron	60–180 µg/dl	Varies daily, little informative on its own
Transferrin saturation	16–45 %	Transport capacity; <16 % = functional deficiency
Hemoglobin	12–16 g/dl (women) / 13.5–17.5 g/dl (men)	Anemia diagnosis

Supplementation: When and Which Form?

In cases of confirmed deficiency (ferritin <30 µg/l) or increased demand, supplementation can be beneficial. Common forms:

Form	Elemental Iron	Tolerability	Bioavailability
Iron sulfate	~20 %	Moderate (GI discomfort possible)	High
Iron gluconate	~12 %	Better tolerated	Good
Iron bisglycinate	~20 %	Very well tolerated	Very high (chelated)
Iron(III)-hydroxide polymaltose	~36 %	Very good	Moderate

Intake recommendation: On an empty stomach or with vitamin C, not together with calcium, tea, or coffee. If tolerability problems arise, switch to chelated iron bisglycinate.

Frequently Asked Questions (FAQ)

Can I take too much iron?

Yes. Iron overload (hemochromatosis or excessive supplementation) generates oxidative stress through the Fenton reaction. Symptoms: joint pain, liver damage, dark skin pigmentation. Healthy individuals without confirmed deficiency should not supplement.

Why is spinach not a good iron source?

While spinach contains a lot of iron on paper (~3.6 mg/100g), it also contains a lot of oxalates, which strongly inhibit absorption. The actual usable amount is small.

How long does it take to replenish iron stores?

With consistent supplementation, ferritin levels usually normalize after 3–6 months. Hemoglobin normalizes faster (4–8 weeks), but ferritin takes longer.

Iron and exercise – what to consider?

Endurance athletes, especially runners, lose iron through foot-strike hemolysis, sweat, and increased turnover. Regular ferritin checks (twice a year) are recommended.