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Completed

NCT Number: NCT07720960

Effects of Intermittent Hypoxia Training With Iron Supplementation on Red Blood Cells and Iron Levels in Trained Athletes

This study investigates how training under conditions of reduced oxygen (intermittent hypoxia) affects the body's ability to produce red blood cells and manage iron levels, compared to training under normal oxygen conditions. Red blood cells are essential for transporting oxygen throughout the body, and their production depends on having enough available iron.

Thirty-two physically trained participants completed a 3-week training program, either in low-oxygen conditions or in normal oxygen conditions. All participants followed the same diet and received daily supplements of iron and vitamins to ensure adequate nutritional support.

The main hypothesis of this study is that training in low-oxygen conditions stimulates the production of red blood cells more strongly than training in normal oxygen conditions, and that this increased production requires the body to use stored iron, potentially lowering iron reserves.

Results showed that participants training in low-oxygen conditions experienced a greater increase in red blood cells and related markers compared to those training in normal conditions. At the same time, their stored iron levels decreased, suggesting that the body was using its iron reserves to support the increased production of red blood cells. In contrast, participants training in normal oxygen conditions showed smaller changes and maintained or slightly increased their iron stores.

These findings suggest that low-oxygen training can enhance the body's capacity to produce red blood cells but may also reduce iron reserves. This highlights the importance of monitoring iron levels during such training programs, especially in athletes or individuals with conditions related to low oxygen availability, such as anemia.

Overall, this study aims to improve understanding of how oxygen availability influences blood health and may help guide future strategies that combine hypoxia training and iron supplementation to support performance and treat certain medical conditions.

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Key information

Conditions

Hypoxia Erythropoiesis Iron Metabolism Disorders Metabolic Diseases Nutritional and Metabolic Diseases Pathological Conditions, Signs and Symptoms Signs and Symptoms Signs and Symptoms, Respiratory

Age range

18 year–60 year

Sex eligibility

Male

Study type

Interventional

Phase

Not applicable

Primary location

University Miguel Hernández of Elche

Elche, Alicante, 03202, Spain

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Male sex
  • Adult age (≥18 years)
  • Federated mountain sports practitioner (alpinist, trail runner, ski mountaineer, or endurance runner)
  • Normal hemoglobin levels at screening (≥13 g/dL)
  • Residence at elevations below 700 m
  • Provision of written informed consent prior to enrollment
  • Agreement to comply with the principles of the Declaration of Helsinki (WMA, 2024 revision)

Exclusion criteria

  • Stay at altitudes above 2,000 m within the previous 2 months prior to enrollment
  • Any form of anemia at screening (hemoglobin <12-13 g/dL)
  • Sports-related pseudoanemia
  • Presence of cardiovascular or respiratory pathologies, as determined by the medically supervised VO₂max exercise test
  • Female sex

Treatment and study plan

Control group (CG)

Other

3-week normoxic training program (14 sessions, 90 min/session) with identical exercise structure to the hypoxia group (strength-resistance circuit + cycling intervals), performed at sea-level oxygen conditions inside the same tent to ensure blinding. Frequency: 4-5 sessions/week. All participants received daily oral supplementation: iron 60 mg (ferrous sulfate + ferrous fumarate) + vitamin C 200 mg + folic acid 200 µg + vitamin B12 6 µg. Diet provided ~55 kcal/kg/day (carbohydrates 7-8 g/kg, protein 1.6-2 g/kg, fat 1-1.5 g/kg).

Hypoxia group (HG): trained at simulated altitudes between 4,450 and 5,850 m

Other

3-week normobaric intermittent hypoxia training program (14 sessions, 90 min/session: 60 min active + 30 min passive hypoxia) at simulated altitudes of 4,450-5,850 m (SaO₂ ~80%). Training combined strength-resistance circuit (30 min) and high-intensity cycling intervals (30 min). Frequency: 4-5 sessions/week. All participants received daily oral supplementation: iron 60 mg (ferrous sulfate + ferrous fumarate) + vitamin C 200 mg + folic acid 200 µg + vitamin B12 6 µg. Diet provided ~55 kcal/kg/day (carbohydrates 7-8 g/kg, protein 1.6-2 g/kg, fat 1-1.5 g/kg).

Primary outcomes

  1. Hemoglobin concentration

    Time frame: Baseline and 3 weeks (end of intervention)

    Venous blood hemoglobin concentration (g/dL) measured at baseline and 3 days after completion of the 3-week intervention. Blood samples collected in the morning (08:00-10:00 h) after overnight fast (≥8 h) and 10 min of seated rest, analyzed by automated laboratory analyzer following CLSI standards.

Secondary outcomes

  1. Red blood cell count

    Time frame: Baseline and 3 weeks (end of intervention)

    Venous blood erythrocyte concentration (×10⁶ cells/mm³) measured at baseline and 3 days after completion of the 3-week intervention. Blood samples collected in the morning (08:00-10:00 h) after overnight fast (≥8 h) and 10 min of seated rest, analyzed by automated laboratory analyzer following CLSI standards.

  2. Hematocrit

    Time frame: Baseline and 3 weeks (end of intervention)

    Percentage of red blood cells in total blood volume (%) measured at baseline and 3 days after completion of the 3-week intervention. Blood samples collected under identical conditions to primary outcome measure.

  3. Serum ferritin

    Time frame: Baseline and 3 weeks (end of intervention)

    Serum ferritin concentration (ng/mL) as an indicator of iron storage status, measured at baseline and 3 days after completion of the 3-week intervention. Obtained from serum separator tubes analyzed by automated laboratory analyzer following CLSI standards.

  4. Reticulocyte count

    Time frame: Baseline and 3 weeks (end of intervention)

    Percentage of reticulocytes (immature red blood cells) in peripheral blood (%), used as an indirect indicator of erythropoietic activity. Measured at baseline and 3 days after completion of the 3-week intervention under identical sampling conditions.

Sponsors and collaborators

Lead sponsor

Néstor Vicente-Salar

Other

Registry information

Official study title

SHORT-TERM INTERMITTENT HYPOXIA TRAINING INDUCES POSITIVE ERYTHROPOIETIC ADAPTATIONS BUT DECREASING DRASTICALLY IRON RESERVES

Acronym: IHIT-IRON

Important dates

Study start
2011
Primary completion
2014
Study completion
2014
First posted
Jul 22, 2026
Registry last updated
Jul 22, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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