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

NCT07720960 | Completed

• 1 other identifier: PS09/01093
• Study Type: interventional
• Target: 32
• Locations: 1 country
• Sites: 1

Brief Summary

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.

Conditions

Hypoxia; Erythropoiesis; Iron Metabolism Disorders

Outcome Measures

Primary Outcomes (1)

• Hemoglobin concentration

  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.

  Baseline and 3 weeks (end of intervention)

Secondary Outcomes (4)

• Red blood cell count

  Baseline and 3 weeks (end of intervention)

• Hematocrit

  Baseline and 3 weeks (end of intervention)

• Serum ferritin

  Baseline and 3 weeks (end of intervention)

• Reticulocyte count

  Baseline and 3 weeks (end of intervention)

Study Arms (2)

Control group (CG)

PLACEBO COMPARATOR

Trained at sea-level conditions

Other: Control group (CG)

Hypoxia group (HG)

EXPERIMENTAL

Trained at simulated altitudes between 4,450 and 5,850 m

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

Interventions

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).

Control group (CG)

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).

Hypoxia group (HG)

Eligibility Criteria

• Age: 18 Years - 60 Years
• Sex: male
• Healthy Volunteers: Yes
• Age Groups: Adult (18-64)

You may qualify if:

• 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)

You may not qualify if:

• 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

Sponsors & Collaborators

• Néstor Vicente-Salar: lead

Study Sites (1)

University Miguel Hernández of Elche

Elche, Alicante, 03202, Spain

Location

MeSH Terms

Conditions

Hypoxia; Iron Metabolism Disorders

Interventions

Control Groups

Condition Hierarchy (Ancestors)

Signs and Symptoms, Respiratory; Signs and Symptoms; Pathological Conditions, Signs and Symptoms; Metabolic Diseases; Nutritional and Metabolic Diseases

Intervention Hierarchy (Ancestors)

Epidemiologic Research Design; Epidemiologic Methods; Investigative Techniques; Research Design; Methods

Study Officials

• Enrique Roche, Full Professor

  University Miguel Hernández of Elche

  STUDY DIRECTOR

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: PARTICIPANT
• Purpose: TREATMENT
• Intervention Model: PARALLEL
• Sponsor Type: OTHER
• Responsible Party: SPONSOR INVESTIGATOR
• PI Title: Asscociate Professor

Model Details: Participants were assigned to one of two parallel groups: a hypoxia training group (HG) or a normoxic control group (CG). Allocation followed an alternating sequence as participants enrolled. Both groups completed the same structured 3-week training program (4-5 sessions/week; 90 min/session), consisting of combined strength-resistance and aerobic exercise performed inside an environmental tent. The HG trained under normobaric intermittent hypoxia (simulated altitude 4,450-5,850 m), while the CG trained under normoxic conditions, with participants blinded to the environmental setting. Each session included 60 min of active training and 30 min of passive exposure. Physiological variables (oxygen saturation, heart rate, lactate, workload relative to VO₂max) were continuously monitored.

Study Record Dates

• First Submitted: July 17, 2026
• First Posted: July 22, 2026
• Study Start: October 23, 2011
• Primary Completion: June 30, 2014
• Study Completion: July 15, 2014
• Last Updated: July 22, 2026

Record last verified: 2014-12

Data Sharing

• IPD Sharing: Will not share

Locations

ES (1)