HypoxiaIHIT-IRONNCT07720960
Effects of Intermittent Hypoxia Training With Iron Supplementation on Red Blood Cells and Iron Levels in Trained Athletes
A study testing Hypoxia group (HG): trained at simulated altitudes between 4,450 and 5,850 m in people with Hypoxia and Erythropoiesis, run by Néstor Vicente-Salar at 1 site in Spain.
Trial 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. Read more about this study
- Who is it for?
- Ages 18 to 60 years, men onlyHealthy volunteers can take part
- Conditions the study is for
- Hypoxia, Erythropoiesis, Iron Metabolism Disorders
- What is being tested?
- Hypoxia group (HG): trained at simulated altitudes between 4,450 and 5,850 m
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 32 participants
- Where
- 1 siteSpain
- Study dates
- 23 Oct 2011to 15 Jul 2014
- Phase
- Interventional
- Are there results?
- None posted in the registry
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 to 60 years
- Men only
- Healthy volunteers accepted
- Adult
Who may be able to join
- 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)
Who cannot join
- 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
Trial locations and contacts
1 site in 1 country.
About this study
Official title: SHORT-TERM INTERMITTENT HYPOXIA TRAINING INDUCES POSITIVE ERYTHROPOIETIC ADAPTATIONS BUT DECREASING DRASTICALLY IRON RESERVES
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.
Read more
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
- Being tested
- Control group (CG), Hypoxia group (HG): trained at simulated altitudes between 4,450 and 5,850 m
- Medical subject headings
- Hypoxia, Iron Metabolism Disorders
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
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 mOther
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).
| Study group | Role | What they receive |
|---|---|---|
| Control group (CG) | Placebo comparator | Trained at sea-level conditions Receives: Other: Control group (CG) |
| Hypoxia group (HG) | Experimental | Trained at simulated altitudes between 4,450 and 5,850 m Receives: Other: Hypoxia group (HG): trained at simulated altitudes between 4,450 and 5,850 m |
What is being measured
The primary outcome is the main question the study is designed to answer.
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.
Measured: Baseline and 3 weeks (end of intervention)
Secondary outcomes (4)
Red blood cell count
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.
Measured: Baseline and 3 weeks (end of intervention)
Hematocrit
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.
Measured: Baseline and 3 weeks (end of intervention)
Serum ferritin
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.
Measured: Baseline and 3 weeks (end of intervention)
Reticulocyte count
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.
Measured: Baseline and 3 weeks (end of intervention)
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted22 Jul 2026
- Study start23 Oct 2011
- Primary completion30 Jun 2014
- Study completion15 Jul 2014
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for HypoxiaStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase N/A
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- 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.
- Masking
- Single blind
- Who is masked
- Participant
- Enrolment
- 32 participants (actual)
Sponsor and investigators
- Lead sponsor
- Néstor Vicente-Salar
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor-investigator, Néstor Vicente-Salar, Universidad Miguel Hernandez de Elche
- Investigators
- Enrique Roche, Full Professor, Study director, University Miguel Hernández of Elche
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07720960
- Sponsor's protocol ID
- PS09/01093
- Acronym
- IHIT-IRON
- Status last verified
- Dec 2014
- First submitted
- 17 Jul 2026
- Last updated
- 22 Jul 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- No
Study at a glance
From the registry record, last updated by the sponsor on 22 Jul 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- SHORT-TERM INTERMITTENT HYPOXIA TRAINING INDUCES POSITIVE ERYTHROPOIETIC ADAPTATIONS BUT DECREASING DRASTICALLY IRON RESERVES
- ClinicalTrials.gov ID
- NCT07720960
- Acronym / sponsor ID
- IHIT-IRON / PS09/01093
- Conditions
- Hypoxia, Erythropoiesis, Iron Metabolism Disorders
- Study type
- Interventional
- Recruitment status
- Completed
- Enrolment
- 32 participants (actual)
- Lead sponsor
- Néstor Vicente-SalarUniversity, hospital or other
- Study start
- 23 Oct 2011 (actual)
- Primary completion
- 30 Jun 2014 (actual)
- Study completion
- 15 Jul 2014 (actual)
- First posted
- 22 Jul 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
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.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Single blind (participant)
- Number of arms
- 2
- Model description
- 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.
| Arm | Type | Receives |
|---|---|---|
| Control group (CG) | Placebo comparator | Other: Control group (CG)Trained at sea-level conditions |
| Hypoxia group (HG) | Experimental | Other: Hypoxia group (HG): trained at simulated altitudes between 4,450 and 5,850 mTrained at simulated altitudes between 4,450 and 5,850 m |
Who may qualify
- Ages
- 18 to 60 years
- Sex
- Male only
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (7 listed)
- 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
Key exclusion criteria (5 listed)
- 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
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| Control group (CG)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). | Other | Control group (CG) |
| Hypoxia group (HG): trained at simulated altitudes between 4,450 and 5,850 m3-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). | Other | Hypoxia group (HG) |
Primary outcome
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.
4 secondary outcomes
Red blood cell count
Time frame: Baseline and 3 weeks (end of intervention)
Hematocrit
Time frame: Baseline and 3 weeks (end of intervention)
Serum ferritin
Time frame: Baseline and 3 weeks (end of intervention)
Reticulocyte count
Time frame: Baseline and 3 weeks (end of intervention)
Results and safety
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 22 Jul 2026.
- Individual participant dataSharing planned: No
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Enrique Roche, Full Professor study director
University Miguel Hernández of Elche
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing Hypoxia group (HG): trained at simulated altitudes between 4,450 and 5,850 m in people with Hypoxia and Erythropoiesis, run by Néstor Vicente-Salar at 1 site in Spain.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 7 inclusion and 5 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: finished, as of the sponsor's last update on 22 Jul 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Spain. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
Are results available for this study?
The study is completed, but results are not available in the source record. That does not mean the treatment did or did not work.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Hemoglobin concentration (time frame: Baseline and 3 weeks (end of intervention)). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 22 Jul 2026.