Improving iron levels in young female endurance, intermittent, and power/strength athletes aged 16-35

Iron Revisited: Alternate-Day Oral Iron Supplementation in Endurance, Intermittent, and Power/Strength Athletes

This trial will test whether different types and doses of oral iron supplements, taken every other day for 12 weeks, help young female athletes with low iron stores improve iron levels, gut health, and exercise performance while causing fewer stomach symptoms.

Quick facts

• Phase: Not applicable
• Study type: Interventional
• Enrollment: 36 (estimated)
• Ages: 16 Years to 35 Years
• Sex: Female
• Sponsor: University of Calgary (Academic / other)
• Drugs / interventions: radiation
• Locations: 1 site (Calgary, Alberta)
• Trial ID: NCT06942208 on ClinicalTrials.gov

What this trial studies

This randomized interventional study assigns biologically female athletes aged 16–35 with suboptimal ferritin (≤50 µg/L) to one of three oral iron regimens: low-dose iron (40 mg), low-dose yeast-bound iron (40 mg Lalmin® Fe10), or high-dose iron (150 mg), taken every other day for 12 weeks. Researchers will measure iron status (including ferritin and hemoglobin), gastrointestinal symptoms, gut microbiota composition, and athletic performance using cycling and jumping tests before and after the intervention. Supplements are encapsulated, participants are randomized, and adherence, side effects, and energy-availability criteria are monitored throughout. The design aims to identify which supplement dose and formulation best improves iron stores while minimizing gastrointestinal distress in highly trained young female athletes.

Who should consider this trial

Good fit: Ideal candidates are biologically female athletes aged 16–35 who are competitively trained (Tier 3–4), have suboptimal ferritin (≤50 µg/L), are not anemic (hemoglobin ≥120 g/L), meet energy-availability requirements, and can attend in-person testing at the University of Calgary.

Not a fit: Those unlikely to benefit include people who are anemic (hemoglobin <120 g/L), outside the 16–35 age range, not biologically female athletes, regular users of prebiotics/probiotics or laxatives, smokers, heavy alcohol users, recent blood donors, or those unable to attend in-person visits.

Why it matters

Potential benefit: If successful, the results could point to a lower-dose or yeast-bound iron option that raises iron stores and supports performance with fewer gastrointestinal side effects.

How similar studies have performed: Prior research indicates alternate-day low-dose oral iron can improve iron status with fewer side effects, but yeast-bound iron preparations have been less widely studied in elite athletes.

Eligibility criteria

Inclusion Criteria:

* Biologically female athlete
* Age 16-35
* At least one year past the age of menarche
* Complete and pass the Get Active Questionnaire (GAQ)
* Suboptimal ferritin levels (≤50 mcg/L)
* Provide informed consent to participate in study
* Activity level based on Participant Classification Framework (McKay et al., 2022)

  * Tier 3: Highly Trained / National Level
  * Tier 4: Elite / International Level
* Energy availability \>30 kcal/kg LBM
* Have access to a smartphone, tablet, or computer
* Able to swallow a capsule sized 25mm length and 8mm width (i.e. large dose omega 3 pill)

Exclusion Criteria:

* Non-English speaking
* Anemic (hemoglobin \<120g/L)
* Regular prebiotic (fiber) or probiotic use within 4 weeks of study enrollment
* Current laxative use
* Are a smoker or use tobacco products
* Consume \>21 units of alcohol per week
* Have donated blood in the previous 3 months
* Have a BMI \<16 but \>30kg/m2
* Are dieting for weight loss or are following a low carbohydrate diet
* Have participated in another clinical trial within the 30 days preceding study enrollment.
* Known allergy of hypersensitivity to any ingredient, including non-medicinal ingredients, such as iron, yeast, cellulose, or maltodextrin
* Are taking medications known to affect cardiovascular or metabolic responses to exercise such as beta-blockers, anti-coagulants etc. as assessed by the Principal Investigator
* Known history of thalassemia or thalassemia trait
* Known inherited bleeding disorder
* Major surgery in the past 3 months
* Chronic use of Salicylates, aspirin, corticosteroids, or nonsteroidal anti-inflammatory drugs
* Have any of the following conditions: renal or gastrointestinal disorders, autoimmune disease, metabolic disease, heart disease, vascular disease, rheumatoid arthritis, diabetes, poor lung function, uncontrolled blood pressure, dizziness, thyroid problems, or any other health conditions that are being treated and deemed to be able to significantly interfere with study intervention and assessment in the opinion of the Principal Investigator and Qualified Investigator
* Have current musculoskeletal injuries that limit exercise capacity
* Self-identifying with any kidney or gastrointestinal issues, metabolic disorders, cardiac conditions, vascular illnesses, rheumatoid arthritis, diabetes, compromised lung function, unregulated blood pressure, episodes of dizziness, thyroid complications, or any other health conditions under treatment that might potentially interfere with the study results
* Orthopaedic issues that limit exercise ability
* Currently/last 3 months taking prescription medications that are known to affect iron absorption (i.e. Antacids/PPIs (e.g., omeprazole), H2 Blockers (e.g., ranitidine), Tetracycline Antibiotics (e.g., doxycycline), Quinolone Antibiotics (e.g., ciprofloxacin), Cholestyramine, Colchicine, Methyldopa.)
* Currently taking levodopa or levothyroxine
* Currently/last 3 months taking iron containing supplements
* Are pregnant or lactating or planning to become pregnant for the duration of the study. All participants must agree to use a medically approved method of birth control for the duration of the study. All hormonal birth control must have been in use for a minimum of three months. Acceptable methods of birth control include:

  * Abstinence or agrees to use contraception if planning to become sexually active
  * Hormonal contraceptives including oral contraceptives, hormone birth control patch
  * Vaginal contraceptive ring, injectable contraceptives, or hormone implant
  * Barrier methods (e.g. condoms with spermicide, diaphragms with spermicide)
  * Intrauterine devices
  * Non-heterosexual lifestyle or agrees to use contraception if planning on changing to heterosexual partner(s)
  * Vasectomy of partner at least 6 months prior to screening

Additional exclusion criteria based on use of SIMBA capsules. Following is a summary of SIMBA capsules specific exclusion criteria:

* Currently pregnant, planning to become pregnant, or breastfeeding
* Prior gastrointestinal disease, surgery, or radiation treatment which, in the Investigator's opinion, would lead to intestinal structuring, narrowing, or obstruction with a risk of capsule non-excretion, including, e.g. achalasia, eosinophilic esophagitis, any IBD, or previous esophageal, gastric, small intestinal, or colonic surgery. Appendectomy or cholecystectomy more than 3 months before the screening visit is acceptable.
* History of known structural gastrointestinal abnormalities such as structures or fistulas leading to mechanical obstruction
* Have any gastrointestinal inflammatory diseases, including ulcerative colitis, Crohn's disease, microscopic colitis.
* Use of any medication in the week prior to the screening study visit, unless part of regular treatment, that could substantially alter gastrointestinal motor function (e.g. opioids, prokinetics, anticholinergics, GLP-1 analogues); laxative use is allowed if it is kept unchanged in the week prior to the study visit. Proton pump inhibitors (PPIs) are allowed provided a wash-out period of 48 hours is respected before swallowing the SIMBA capsules and PPI treatment is resumed only 4 hours thereafter.

  * Prokinetic (stimulate muscle contractions, Metoclopramide, Domperidone, Prucalopride, etc.) use. If you are not using prokinetics to treat SIBO, then you may be eligible after a 2-week washout period, and willing to not use prokinetics for the study duration.
  * Unable to stop using laxatives or prokinetic medications for 4 days before the study procedure (breath test). Laxatives can be resumed after the test is conducted.
* Have used antibiotics (except for topical use) in the previous 12 weeks. You may be eligible to participate once a 12-week washout is completed
* Regular use of probiotics, prebiotics, or synbiotics (including food and drinks containing added probiotics and/or probiotic yogurts with live, active cultures)
* Have digestive problems that slow or stop food from moving properly, like a slow stomach, blocked intestines, or stiffened tissues
* Suffer from celiac disease (treated or untreated)
* Organic motility disorder, including gastroparesis, intestinal pseudo-obstruction, systemic sclerosis, Ogilvie's syndrome
* History of oropharyngeal dysphagia, or other swallowing disorder with a risk of capsule aspiration
* Have had a cancer diagnosis or treatment within the past year (non-melanoma skin cancers are acceptable)
* Have trouble swallowing, which could cause a risk of choking on a capsule
* Participants scheduled for an MRI at any time during the study. You may be eligible to participate once your MRI procedure is completed.
* Have constant constipation (IBS-C) defined as a history of less than 3 bowel movements per week
* Any prior fecal microbiota transplantation
* Drug use
* Suffer from alcohol or drug abuse
* Females of childbearing potential will be asked about their likelihood of being pregnant, based on factors such as recent sexual activity or use of contraception. Their self-reported confirmation of non-pregnancy will be accepted unless they express uncertainty. In cases of doubt, a urine beta-HCG pregnancy test will be required for confirmation. If you become pregnant during the course of the study, you should stop taking the supplement immediately and inform the investigators. If you are using a supplement that the investigators have deemed to not interfere with the study's intervention or assessment (e.g. vitamins, omega-3, creatine monohydrate etc.), you will be permitted to continue taking these supplements. In all cases, participants will be instructed to not change the dose of the taken supplement or introduce a new supplement unless it is medically recommended.

Where this trial is running

Calgary, Alberta

• University of Calgary — Calgary, Alberta, Canada (Recruiting)

Study contacts

• Principal investigator: Jane Shearer — University of Calgary
• Study coordinator: Lauren Hundseth

Conditions Iron Deficiency; iron; iron deficiency; athletic performance; female athlete; iron supplements; ferritin; hemoglobin