Improving Iron Levels in Female Endurance, Intermittent, and Power/Strength Athletes Aged 16-35

Overview

The goal of this clinical trial is to learn if different types and doses of oral iron supplements can improve iron levels, athletic performance, and gut health in young female athletes with low iron stores. The main questions it aims to answer are: * Does a low dose of yeast-bound iron improve iron status better than traditional iron supplements? * Do the different iron supplements cause fewer or more gastrointestinal (stomach) symptoms? * How do iron supplements affect exercise performance and gut bacteria? Researchers will compare three types of iron supplements: * A low-dose iron supplement (40 mg) * A low-dose yeast-bound iron supplement (40 mg) * A high-dose iron supplement (150 mg) This will help researchers find out which type of supplement is most effective and easiest on the stomach. Participants will: * Take one of the three assigned iron supplements every other day for 12 weeks * Complete fitness tests before and after the study, including cycling and jumping tests * Give blood samples to measure iron levels * Provide stool and intestinal samples to study gut bacteria * Swallow a SIMBA capsule before and after the study to collect a sample from the small intestine * Complete regular online surveys about sleep, stress, menstrual cycles, and gut symptoms

This clinical trial is designed to evaluate and compare the effects of three oral iron supplementation strategies on iron status, gut microbiota, and athletic performance in young female athletes with suboptimal iron levels. The study compares a low-dose iron supplement, a low-dose yeast-bound iron supplement (Lalmin® Fe10), and a high-dose iron supplement. The primary goal is to identify which iron supplement improves iron status most effectively while minimizing gastrointestinal symptoms and changes to the gut microbiota. The rationale for the study is based on the high prevalence of iron deficiency among female athletes, especially those involved in endurance and high-intensity sports. Iron plays a key role in oxygen transport, energy production, and recovery, making it essential for optimal athletic performance. However, current supplementation practices often lead to poor compliance due to side effects and low absorption rates. The yeast-bound iron product being tested is hypothesized to improve absorption and tolerability by altering the site of absorption and reducing gastrointestinal distress. Participants will be biologically female athletes aged 16-35 with suboptimal ferritin (≤50 µg/L), who are competitively trained and meet strict health and fitness criteria. After screening, eligible participants will be randomly assigned to one of three groups and consume their assigned supplement every other day for 12 weeks. Each supplement will be encapsulated to preserve blinding and consistency. The study involves six in-person visits: Visit 1 - Screening and Consenting: Study investigators will reach out electronically or by phone to individuals interested in participating in the study. At this time, participants will be informed about the study and eligibility will be confirmed. Iron status will be assessed using a ferritin blood test from a forearm venipuncture. Participants with suboptimal ferritin levels (≤50 µg/L) will be asked to complete a 3-day food record over the following week on non-consecutive days. This food intake data will be used to determine energy availability to ensure participants meet the minimum requirement of \>30 kcal/kg lean body mass. Those who do not meet this requirement will be excluded from further participation. Visit 2 - Baseline Testing (Week 0): Eligible participants will return to the lab to undergo baseline testing. This includes another blood draw to confirm iron status, a DXA scan to assess body composition, and a VO2 max test to evaluate aerobic capacity. Participants will also receive a SIMBA capsule, a fecal collection kit, and detailed instructions for home use. Visit 3 - Baseline Testing (Week 0): Approximately 48-72 hours after Visit 2, participants will return to the lab for anaerobic performance testing. They will complete a Wingate cycling test and a counter-movement jump test to assess lower-body power and anaerobic fitness. Following this, participants will begin the 12-week supplementation phase of the study. Nutritional Intervention: Participants will consume an oral iron supplement every other day for 12 weeks. They will be instructed to take the supplement within 30 minutes of morning training, or upon waking if no training is scheduled. Doses are as follows: * 40 mg elemental iron (low-dose group) * 40 mg yeast-bound elemental iron (Lalmin® Fe10 group) * 150 mg elemental iron (high-dose group) Each supplement will be delivered in gelatin capsules. Participants will be instructed to avoid coffee, tea, dairy, and dairy alternatives for at least 2 hours after consumption. If a dose is missed, they will resume dosing the next day and continue on an every-other-day schedule. Capsules will be distributed every four weeks. Participants will complete baseline, weekly, and monthly questionnaires through Qualtrics to report gastrointestinal symptoms, stress, sleep, menstrual health, and supplement adherence. These tools include PROMIS-GI, SRSS, GISQ, and others. Visit 4 - Follow-Up (Week 4): Participants will return to the lab for a follow-up blood draw to monitor iron status and receive their next 4-week supply of capsules. They will also complete another 3-day food log. Visit 5 - Post-Intervention Testing (Week 12): After 12 weeks of supplementation, participants will return for a second VO2 max test. They will return any unused capsules for adherence tracking and be provided instructions for their second SIMBA capsule and fecal sample collection. Visit 6 - Final Testing (Week 12): Participants will complete all post-intervention assessments including blood tests, a DXA scan, the Wingate test, the counter-movement jump test, and submission of the second SIMBA capsule and fecal sample. A final 3-day food log will also be collected. Primary outcomes include changes in markers of iron status (ferritin, hemoglobin, RBC indices). Secondary outcomes include aerobic/anaerobic performance measures, body composition (DXA), substrate metabolism, gut microbiota composition (via fecal and intestinal sampling), and self-reported gastrointestinal symptoms. Safety and tolerability will be monitored at each study visit and through participant self-report. Data will be analyzed using both traditional statistics (e.g., ANOVA) and machine learning methods for complex 'omics' data. Results will inform better supplementation strategies for female athletes and will be shared through academic publications. The study will contribute to a greater understanding of iron supplementation strategies that are effective, tolerable, and beneficial to performance and health.