This randomized, double-blind, active-controlled trial will evaluate the effects of human lactoferrin supplementation combined with low-dose iron on iron status, aerobic performance, and lactate metabolism in exercising women with low ferritin. Approximately 30 healthy, menstruating women aged 18-45 years with serum ferritin <35 µg/L will be enrolled in an 8-week intervention. Participants will be stratified by baseline ferritin status and randomized to receive 100 mg lactoferrin + 5 mg iron, 300 mg lactoferrin + 5 mg iron, or placebo + 5 mg iron daily.

Primary outcomes include changes in ferritin and hematological parameters. Secondary outcomes include VO₂peak, time to exhaustion, and blood lactate responses during standardized treadmill testing.

This study will determine whether lactoferrin enhances iron homeostasis and improves physiological and performance outcomes in exercising women with low iron stores.

Iron deficiency is one of the most common micronutrient deficiencies in women, particularly among those who are physically active. Suboptimal iron status can impair oxygen transport, mitochondrial function, and exercise performance. Although oral iron supplementation is commonly used, gastrointestinal side effects may reduce adherence and limit effectiveness. Lactoferrin, an iron-binding glycoprotein, has emerged as a potential adjunct strategy to improve iron regulation and tolerability.

This study will investigate whether supplementation with human recombinant lactoferrin in combination with low-dose iron improves iron status and exercise-related outcomes in exercising women with low ferritin.

Approximately 30 healthy, menstruating women aged 18-45 years with serum ferritin <35 µg/L will be recruited. Participants will be stratified by baseline ferritin status (<20 µg/L or 20-35 µg/L) and randomized in a double-blind, parallel-group design to receive one of the following for 8 weeks:

100 mg lactoferrin + 5 mg iron 300 mg lactoferrin + 5 mg iron Placebo + 5 mg iron Participants will complete six study visits including screening, baseline, and follow-up assessments at weeks 2, 4, 6, and 8. Assessments will include venous blood sampling for iron-related biomarkers and hematological parameters, as well as inflammatory and metabolic markers. Aerobic performance will be evaluated using VO₂peak testing and time-to-exhaustion treadmill protocols with serial blood lactate measurements.

Additional measures include gastrointestinal symptoms, menstrual symptoms, quality of life, and perceived recovery. Daily supplementation compliance and adverse events will be monitored throughout the intervention.

This trial will provide insight into the role of lactoferrin as an adjunct to iron supplementation for improving iron homeostasis and performance outcomes in active women.

Inclusion Criteria:

• Women, 18 - 45 years of age
• No changes in hormonal contraception use in the past 6 months
• Has a regular menstrual cycle defined as five out of the past six months
• Engaging in ≥5 hours per week of structured endurance exercise (e.g., running, cycling, swimming, rowing) for the past ≥6 months, with ≥3 sessions per week at moderate-to-vigorous intensity (≥70% HRmax or RPE ≥13).
• Training must be consistent, with no interruptions >2 consecutive weeks in the past 6 months and performed with the purpose of improving performance or preparing for a competition or personal goal.
• Exhibit some degree of compromised iron status as depicted by serum ferritin levels below 30 ug/L
• Participation in at least one organized endurance event (e.g., races, competitions, or matches) at the recreational, sub-elite, or elite level, or be actively training for a planned competition within the next 6 months.
• Generally healthy and free of diseases or disorders that impact functioning of the gastrointestinal system.
• No recent or acute infection in the past 30 days and no chronic systemic illness
• No psychiatric condition that, in the investigator's judgment, would impair consent capacity, protocol adherence, or valid completion of questionnaires.
• If psychiatric medication is used: stable regimen for ≥3 months with no anticipated changes during the study
• Body mass index (BMI) 18.5 to 32.5 kg/m2 (Inclusive)
• Non-smoker
• Agrees to not use any new vitamin, mineral, or dietary supplement product until after study completion and to not take any vitamins, minerals or dietary supplements 24 hours prior to any of the study visits.
• Willing and able to maintain consistent diet and physical activity habits
• Participants who become pregnant during the course of the study will be removed from participation
• Willing and able to provide consent and comply with the protocol
• Able to read and understand English at the 6th-grade level and sign the informed consent to participate in the study

Exclusion Criteria:

• History of any food allergies or intolerances that could impact digestive outcomes and history of irritable bowel syndrome, inflammatory bowel disease (Crohn's, ulcerative colitis, celiac), gastroparesis, chronic constipation or diarrhea requiring medication, or GI surgery
• Has any of the following medical conditions: bleeding disorders, active heart or cardiovascular disease, uncontrolled high blood pressure (≥ 140/90 mmHg), renal or hepatic impairment/disease, Type I or II diabetes, any neurologic disease or disorder that may impact cognition or mood, unstable thyroid disease, chronic inflammatory conditions, immune disorders (such as HIV/AIDS), or any medical condition deemed exclusionary by the Principal Investigator (PI)
• Acute illness or infection within the past 30 days
• History of cancer (except localized skin cancer without metastases) within 5 years prior to screening.
• Recently started taking (within the past 90 days or has had their dosage adjusted in the past 90 days) antihypertensives, hypoglycemic medications, GLP1 agonists of any class or type, stimulatory asthma medications, or any other prescription or over-the-counter medication that confound the outcomes measured in this study
• Habitual use of anti-inflammatory medications for 30 days prior to providing
• Current or past diagnosis of bipolar I/II disorder, schizophrenia spectrum or other psychotic disorder; psychiatric hospitalization, suicidal ideation, attempt, or self-harm behavior in the past 12 months
• Initiation, discontinuation, or dose change of any psychotropic medication within the past 3 months, including antidepressants, anxiolytics, antipsychotics, mood stabilizers, stimulants, or sedative-hypnotics
• Subject has an allergy to any ingredients in the study product
• Subject has a history of drug or alcohol abuse in the past 12 months
• Excessive alcohol intake defined as greater than 7 drinks/week or binge episodes
• Any condition or abnormality that in the expert opinion of the PI, participation in the study would compromise the safety of the subject or the quality of the study data.
• Participating in or has participated in another research study within 30 days prior to the screening visit that could confound outcomes
• Currently pregnant or lactating

Individual participant data (IPD) will not be shared due to privacy and confidentiality considerations. Study results will be reported in aggregate form, and no identifiable data will be disclosed.

Participants and study investigators will be blinded to group assignment. Supplements will be provided in identical-appearing forms and labeled by a third party to ensure concealment of allocation throughout the study.