Product Description
Iron deficiency is the most common nutritional deficiency in endurance athletes — and it's not just about low iron. Building and maintaining healthy red blood cells requires a coordinated team of nutrients working together: iron to form hemoglobin, vitamin C to enhance iron absorption, and the B vitamins (B6, B12, and folate) that are essential for the DNA synthesis and cell division involved in actually creating new red blood cells. Supplementing with iron alone addresses only part of the equation.
Thorne Advanced Iron Complex delivers the full picture in a single capsule.
Gentle, High-Absorption Iron – Most iron supplements use ferrous sulfate, a form notorious for causing nausea, constipation, and GI distress. Thorne uses Ferrochel® ferrous bisglycinate chelate — iron bonded to the amino acid glycine — which is absorbed significantly more efficiently through the gut wall and produces substantially fewer GI side effects. Chelated iron is the endurance athlete's choice for long-term iron repletion without the gut compromise.
The Absorption and Production Stack – Iron doesn't absorb well in isolation. Vitamin C directly enhances non-heme iron absorption by keeping iron in its more bioavailable ferrous state. The active forms of B6 (pyridoxal 5'-phosphate), B12 (methylcobalamin), and folate (5-MTHF) then supply the essential cofactors for hemoglobin synthesis and new red blood cell production — ensuring iron goes to work building oxygen-carrying capacity rather than simply accumulating in the bloodstream.
A Meaningful Therapeutic Dose – At 36mg of elemental iron per capsule, this formula delivers a clinically relevant dose for athletes actively repleating iron stores — twice the 18mg daily value and higher than Thorne's standalone Iron Bisglycinate (25mg). The flexible 1–3 capsule daily dosing allows practitioners to tailor the protocol to individual ferritin levels and repletion targets.
Iron deficiency is particularly prevalent in female endurance athletes, high-volume runners (due to foot-strike hemolysis), plant-based athletes, and those training at altitude. Signs include unexplained fatigue, shortness of breath during efforts that should feel easy, decreased performance, cold extremities, and poor recovery. If you're experiencing these symptoms and your nutrition is otherwise dialed in, iron status is the first place to look.
How to Use Thorne Advanced Iron Complex
Standard Dose: Take 1 capsule one to three times daily with food, or as recommended by your healthcare practitioner. Taking with food reduces the chance of any GI sensitivity.
Timing: Avoid taking iron supplements within two hours of coffee, tea, calcium supplements, or antacids — all of which can reduce iron absorption. Spacing iron away from these significantly improves uptake.
Pro Tip: Get your ferritin tested before and after supplementing. Athletes need ferritin above 35–50 ng/mL for optimal oxygen transport — not just hemoglobin within the normal range. Track your levels every 8–12 weeks during active repletion.
- Gluten free
Supplement Facts
60 Servings
Serving Size: One Capsule
Serving Per Container: 60
| Amount Per Serving | ||
|---|---|---|
| % Daily Value* | ||
| Vitamin C (as Ascorbic Acid) 15mg | ** | |
| Vitamin B6 (as Pyridoxal 5'-Phosphate) 5mg | ** | |
| Folate (400 mcg as L-5-Methyltetrahydrofolate from L-5-Methyltetrahydrofolica Acid, Glucosamine Salt) 667mcg DFE | ** | |
| Vitamin B12 (as Methylcobalamin) 300mcg | ** | |
| Iron (as Ferrochel® Ferrous Bisglycinate Chelate) 36mg | ** | |
* Percent Daily Values are based on a 2,000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.
** Daily Value (DV) not established
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Thorne Advanced Iron Complex FAQ's
Everything you need to know before getting started.
Several training-related mechanisms deplete iron in endurance athletes: foot-strike hemolysis (repetitive impact destroys red blood cells), heavy sweat losses, chronic inflammation from high volume, and GI blood loss in runners. Female athletes lose additional iron through menstruation. Plant-based and vegetarian athletes absorb significantly less iron from food. High-altitude training increases red blood cell demand. The cumulative effect makes iron one of the most common nutritional deficiencies in serious endurance athletes.
Ferrochel® ferrous bisglycinate chelate is iron bonded to two glycine molecules. This chelated structure is absorbed through a separate pathway in the gut wall that bypasses much of the competition and irritation that makes standard iron forms hard to tolerate. The result: significantly better absorption and dramatically fewer GI side effects — no nausea, constipation, or dark stools that derail long-term supplementation compliance.
Building a red blood cell requires more than just iron. The synthesis of hemoglobin and the cell division that produces new red blood cells depend on adequate B6, B12, and folate working in concert with iron. Thorne uses the active forms of all three — pyridoxal 5'-phosphate (B6), methylcobalamin (B12), and 5-MTHF (folate) — to ensure the cofactors are available in immediately usable form regardless of an athlete's genetic ability to convert standard vitamin precursors.
Thorne Iron Bisglycinate is a standalone iron supplement at 25mg — ideal for athletes doing routine maintenance or who only need iron without additional cofactors. Advanced Iron Complex delivers a higher iron dose (36mg) alongside the full B vitamin and vitamin C cofactor stack for athletes actively repleating depleted iron stores or who need comprehensive blood-building support. For maintenance, Iron Bisglycinate is sufficient. For active repletion, Advanced Iron Complex is the more complete formula.
Take with food to minimize GI sensitivity. Avoid taking within two hours of coffee, tea, dairy, calcium supplements, or antacids — all of which significantly reduce iron absorption. Vitamin C is already included in the formula to optimize absorption, so no additional vitamin C supplementation is needed at the same time.