Supporting thyroid health with iron

Thyroid health is a central pillar of women’s metabolic and hormonal balance, influencing energy, mood, menstrual regularity, and long-term wellness. It is estimated that up to 15% of adult women of reproductive age—and potentially up to 20% of menopausal women—have some form of thyroid dysfunction.¹ With the increased attention on women’s health, it is perhaps unsurprising that there are multiple supplements targeting thyroid health; however, the majority focus on iodine, selenium, and even adaptogenic botanicals, with most missing a foundational nutrient for thyroid hormone synthesis and function: iron.

Iron is a cofactor for key enzymes in thyroid hormone production. It is required for the activity of thyroid peroxidase (TPO), the heme-containing enzyme that catalyzes the oxidation of iodide and the iodination of thyroglobulin, the indispensable steps in producing thyroxine (T4) and triiodothyronine (T3). When iron availability is low, TPO activity is compromised, blunting the thyroid’s ability to manufacture hormones efficiently.² Animal research reinforces this mechanism: iron-deficient diets in rodents reduce both T3/T4 levels and TPO activity, demonstrating a direct functional link between iron status and thyroid metabolism.³

Investigating the Impact

In the United States, absolute and functional iron deficiency are common among adult and adolescent females, with estimates ranging up to 40% of absolute deficiency.⁴ Yet even moderately low iron levels are associated with altered thyroid hormone profiles. A 2023 systematic review and meta-analysis pooling data from multiple studies found that individuals with low iron status had significantly lower serum TSH, free T4 (FT4), and free T3 (FT3) compared to those with normal iron status.⁵ The meta-analysis also showed a positive correlation between serum ferritin and thyroid hormone levels, suggesting that iron stores are directly related to thyroid hormone profiles.

Other clinical data support this relationship in specific cohorts. For example, a retrospective analysis of women with low ferritin showed that iron supplementation over six weeks significantly lowered elevated TSH levels, particularly in those with evidence of subclinical hypothyroidism, highlighting the potential clinical impact of correcting iron deficiency on thyroid activity.⁶ Cross-sectional studies further reinforce that nutritional iron deficiency correlates with reduced serum T3 and T4 and impaired peripheral thyroid hormone conversion.⁷

Evidence suggests that improving iron status can enhance thyroid function. A combination of iron and iodine supplementation in iron-deficient adolescent girls demonstrated that increases in iron stores were accompanied by improvements in several thyroid hormone indices when compared with iodine or placebo alone.⁸ Smaller clinical studies and case reports also point to improvements in metabolic markers and thyroid hormone dynamics when iron deficiency is corrected, especially in women with concurrent anemia and thyroid imbalance. These findings hint at practical benefits of supplementation in targeted populations, although more large-scale research is warranted.

Meeting the Market Need

It is perhaps not surprising that women are at higher risk of thyroid dysfunction as well as iron deficiency. The overlap of those vulnerabilities creates a compelling case for developing thyroid support products that integrate iron alongside key synergists including iodine, selenium, and zinc. Integrating a bioavailable form of iron into a formulation targeting women who are seeking to improve thyroid health to optimize energy and metabolism opens a new opportunity to educate consumers about the ‘why’ around iron supplementation.

However, bioavailability and tolerability matter when looking at iron ingredients. There is great variability in terms of absorption efficiency and the potential for gastrointestinal side effects. For a combination formula, companies can turn to enhancers such as vitamin C, or look to unique forms such as ferritin iron, which is absorbed via a unique and dedicated absorption mechanism in humans. According to Douglas Kalman, PhD, RD, this form of iron is underappreciated, although its science positions it to become more of the norm for formulators and consumers. As he explains, “Unlike other forms of iron, this form utilizes receptor-mediated endocytosis, which physically absorbs the protein shell containing the iron and other minerals in an efficient manner.”

Supplements that provide highly absorbable iron, paired with targeted cofactors, can address an unmet need in the women’s health market and support more consistent consumer outcomes.

References

1. Brown, E.D.L.; Obeng-Gyasi, B.; Hall, J.E.; Shekhar, S. The Thyroid Hormone Axis and Female Reproduction. Int. J. Mol. Sci. 2023, 24(12), 9815. DOI: 10.3390/ijms24129815
2. Szklarz, M.; Gontarz-Nowak, K.; Matuszewski, W.; Bandurska-Stankiewicz, E. Iron: Not Just a Passive Bystander in AITD. Nutrients 2022, 14(21), 4682. DOI: 10.3390/nu14214682
3. Hess, SY.; Zimmermann, MB.; Hurrell, RF. Iron Deficiency Anemia Reduces Thyroid Peroxidase Activity in Rats. J Nutr. 2002. 132(7), 1951-1955. DOI: 1951-1955, DOI: 10.1093/jn/132.7.1951.
4. Tawfik, YMK.; Billingsley, H, Bhatt, AS, et al. Absolute and Functional Iron Deficiency in the US, 2017-2020. JAMA Netw Open. 2024;7(9):e2433126. DOI: 10.1001/jamanetworkopen.2024.33126
5. Garofalo, V.; Condorelli, R.A.; Cannarella, R.; Aversa, A.; Calogero, A.E.; La Vignera, S. Relationship between Iron Deficiency and Thyroid Function: A Systematic Review and Meta-Analysis. Nutrients 2023, 15(22), 4790. DO: 10.3390/nu15224790
6. Jashi,L.; Peshkova T.; shervashidze, t.; Artmeladze, M.; Kamashidze K.;, Gorgiladze, N.; Kotorashvili, A. Iron deficiency and thyroid dysfunction: impact of iron supplementation on tsh levels in women of reproductive age in ajara georgia. Endocrine Abstracts. 2025. 110, 1157. DOI: 10.1530/endoabs.110.P1157
7. Chatterjee, S.; Chakrabarti, P.; Sinhamahapatra, P. Relationship between iron metabolism and thyroid hormone profile in hypothyroidism. International Journal of Research in Medical Sciences, 2021. 9(3), 790–793. DOI: 10.18203/2320-6012.ijrms20210879
8. Eftekhari, M.; Simondon, KB.; Jalali, M. et al. Effects of administration of iron, iodine and simultaneous iron-plus-iodine on the thyroid hormone profile in iron-deficient adolescent Iranian girls. Eur J Clin Nutr 2006. 60, 545–552. DOI: 10.1038/sj.ejcn.1602349