If you’ve been told you’re iron deficient but the supplements leave you constipated, nauseous, wired or still exhausted, we need to zoom out. Because anaemia is rarely just an iron story. And in clinic, especially in women with fatigue, hair loss, cold intolerance and stubborn low ferritin, thyroid function is often sitting quietly in the background, unaddressed.
Decades ago, Broda Barnes was already observing something most practitioners still miss. He saw chronic anaemia resolve when thyroid function was corrected, sometimes without iron at all. His reasoning was not alternative or mystical. It was physiological. Thyroid hormone drives metabolic rate. The bone marrow is metabolically active tissue. If thyroid output drops, red blood cell production slows. Oxygen demand falls. The body adapts by making fewer red blood cells. In that model, anaemia is a downstream effect of low thyroid function. Correct the thyroid, restore metabolic rate, haemoglobin rises.
A classic study from 1975 examined erythropoiesis (red blood cell formation) in patients with overt hypothyroidism and found a significant reduction in bone marrow red cell production and red cell mass compared with normal controls, with lower erythropoietin levels consistent with decreased metabolic drive in hypothyroidism. This was interpreted as a physiological adjustment to reduced oxygen requirements in low metabolic states.
Meta-analysis data show that people with hypothyroidism, both overt and subclinical, have higher odds of anaemia than euthyroid individuals, and that reduced thyroid function is associated with lower haemoglobin levels.
In contrast, there are physiological studies showing that thyroid hormones stimulate erythroid progenitor cells, enhance erythropoietin production, and increase red blood cell production, which supports the core idea Barnes proposed (that low thyroid function can lead to anaemia, even without iron deficiency).
Energy, Minerals and Iron Dysregulation
Then you have Morley Robbins, who reframed the iron conversation entirely. He argues that what is labelled “iron deficiency anaemia” is often iron mismanagement. Copper is required to mobilise iron, transport it and insert it into haemoglobin. Without adequate copper and retinol, iron becomes dysregulated. It accumulates in tissues yet fails to be properly utilised. Blood work can show low serum iron and low haemoglobin, while ferritin appears normal or even elevated. The issue is not absence. It is dysfunction.
In this model, low copper impairs mitochondrial respiration. Reduced mitochondrial energy suppresses thyroid function. Lower thyroid function further reduces red blood cell production. Anaemia and hypothyroidism appear together because they share the same energetic bottleneck.
Thyroid, Mitochondria and Oxidative Metabolism
Ray Peat took this even deeper into cellular respiration. For him, thyroid hormone is the regulator of oxygen use and ATP production. Every tissue depends on it, including bone marrow. When oxidative metabolism is suppressed, erythropoiesis slows. Iron alone cannot fix that. Iron must be actively incorporated into heme inside functioning mitochondria. If thyroid-driven respiration is low, iron becomes ineffective. Peat viewed anaemia as part of a broader pattern of metabolic suppression, low temperature, low pulse, fatigue, poor stress resilience, all pointing back to insufficient thyroid activity at the cellular level.
Modern pooled analyses published in journals such as The Journal of Clinical Endocrinology & Metabolism show higher rates of anaemia in hypothyroid individuals and improvements in haemoglobin after thyroid treatment. The clinical observations came first. The research followed.
So What Is Really Going On?
In practice, I rarely see this as either-or. You can absolutely have copper dysregulation. You can absolutely have poor dietary intake. And many women do have multiple layers at once. But what I consistently see overlooked is low or suboptimal thyroid function driving the entire pattern. The focus stays on ferritin. The thyroid panel is dismissed as “normal.” The symptoms continue.
I view anaemia in most of the women I work with as a combination. Mineral imbalances matter. Copper and iron dynamics matter. But hypothyroid or low thyroid function is often the unrecognized driver that slows metabolism, impairs oxygen utilization and makes iron therapy ineffective. If your always cold and have cold extremities, raynauds or chilblains in winter then your exactly who I am talking about. When you restore thyroid function and correct mineral balance together, the system finally has the energy to produce and utilize red blood cells properly.
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References
K. C. DAS, M. MUKHERJEE, T. K. SARKAR, R. J. DASH, G. K. RASTOGI, Erythropoiesis and Erythropoietin in Hypo- and Hyperthyroidism, The Journal of Clinical Endocrinology & Metabolism, Volume 40, Issue 2, 1 February 1975, Pages 211–220, https://doi.org/10.1210/jcem-40-2-211
Wopereis DM, Du Puy RS, van Heemst D, Walsh JP, Bremner A, Bakker SJL, Bauer DC, Cappola AR, Ceresini G, Degryse J, Dullaart RPF, Feller M, Ferrucci L, Floriani C, Franco OH, Iacoviello M, Iervasi G, Imaizumi M, Jukema JW, Khaw KT, Luben RN, Molinaro S, Nauck M, Patel KV, Peeters RP, Psaty BM, Razvi S, Schindhelm RK, van Schoor NM, Stott DJ, Vaes B, Vanderpump MPJ, Völzke H, Westendorp RGJ, Rodondi N, Cobbaert CM, Gussekloo J, den Elzen WPJ; Thyroid Studies Collaboration. The Relation Between Thyroid Function and Anemia: A Pooled Analysis of Individual Participant Data. J Clin Endocrinol Metab. 2018 Oct 1;103(10):3658-3667. doi: 10.1210/jc.2018-00481. PMID: 30113667; PMCID: PMC6179176.
https://pubmed.ncbi.nlm.nih.gov/30113667
Zhou G, Ai Y, Guo S, Chen Q, Feng X, Xu K, Wang G and Ma C (2022) Association Between Red Blood Cell Distribution Width and Thyroid Function. Front. Endocrinol. 12:807482. doi: 10.3389/fendo.2021.807482
