The Vegan Marathoner With Ferritin of 16
Priya, 29, has raced competitively for nine years and is 14 weeks out from a spring marathon. She has eaten a self-selected vegan diet for three years and trains 95-110 km per week at 58 kg. Recent bloodwork: ferritin 16 ng/mL (lab reference 15-150), hemoglobin 12.1 g/dL (12.0-15.5), otherwise unremarkable. She reports heavy menstrual bleeding lasting five days each cycle, persistent fatigue, and a resting heart rate eight beats above her usual baseline. Her three-day food recall averages 1,650 kcal on training days, about 55 g protein, no fortified cereals or legumes, and a mug of black tea with every meal. She takes no supplements and has never seen a registered dietitian. She asks whether she should "just buy iron pills at the drugstore" and continue her current mileage.
1. Which findings in Priya's history and labs carry the most weight, and how should the ferritin of 16 ng/mL be interpreted for her specifically?
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Three findings carry the most weight, and none can be read in isolation.
- Ferritin 16 ng/mL is "normal" only against a laboratory range built for sedentary adults. In a heavily training endurance athlete, ferritin below roughly 30 ng/mL with fatigue is consistent with iron deficiency without anemia. Ferritin is also an acute-phase reactant, so inflammation can inflate it; a low value is more informative than a mid-range one, and a "normal" value never rules deficiency out.
- Hemoglobin 12.1 g/dL sits at the bottom of the reference range, but endurance training expands plasma volume and dilutes hemoglobin. That makes the number look better than the iron stores behind it.
- Heavy menstrual bleeding is a plausible primary driver, while 1,650 kcal and about 55 g protein (roughly 0.95 g/kg) point to low energy availability; the elevated resting heart rate fits that picture.
Tea with every meal adds polyphenols that inhibit non-heme iron absorption, and she uses no fortified foods. Iron deficiency and low energy availability are two separate problems presenting together, and the plan has to address both rather than only the supplement question.
2. Prioritize your interventions for the first four weeks, and state clearly what falls outside your scope.
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Priority 1: medical referral, not self-treatment. Ferritin, hemoglobin, transferrin saturation, CRP (to interpret ferritin) and a celiac screen belong to a physician. Oral iron dosing, form and timing are the clinician's decision. Your contribution is coordination: flag that alternate-day dosing is often better tolerated and absorbed than daily dosing, and that follow-up ferritin should not be drawn immediately after starting.
Priority 2: close the energy gap. Move her from roughly 1,650 kcal toward approximately 2,400-2,600 kcal on training days, titrated against weight stability, hunger and recovery rather than a fixed number. Protein to about 1.6 g/kg (roughly 93 g) spread as 25-30 g per meal from tofu, tempeh, lentils, soy milk and seitan.
Priority 3: absorption tactics. Vitamin C sources with meals, tea and coffee between meals instead of with them, fortified cereal or legumes daily, cast-iron cookware.
Priority 4: discuss training load with her coach; mileage may need to hold steady while energy status recovers.
Outside scope: ordering labs, diagnosing iron deficiency anemia, prescribing supplements. Document the referral and continue coaching nutrition.
3. What will you re-measure, when, and what would make you change course?
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Reassessment should be staged, because the markers move at different speeds.
- Symptoms, weekly: fatigue rating, resting heart rate, sleep quality, menstrual flow, and training quality. These respond first and are the earliest signal that the plan is working or not.
- Dietary adherence, weekly: energy intake versus target, protein distribution, and whether tea has actually moved away from meals.
- Body weight and menstrual cycle, monthly: a stable or slowly rising weight with restored cycles supports improved energy availability; continued weight loss at this intake would suggest something else is driving the deficit.
- Bloods, at 8-12 weeks: repeat ferritin, hemoglobin and transferrin saturation with the physician. Ferritin lags and can rise with inflammation, so a single number should not drive dose changes; the trend plus symptoms is the read.
Change course if: gastrointestinal side effects make oral iron intolerable (refer back to the prescriber), fatigue worsens despite intake improvements (re-examine training load, sleep and thyroid), or weight climbs faster than intended. If ferritin has not moved by 12 weeks despite consistent intake and supplementation, that points to absorption, ongoing blood loss, or an inflammatory process, and the physician needs to know.