Thyroid Health Biomarkers
Thyroid-stimulating hormone (TSH) is a crucial biomarker for testing thyroid imbalances. Elevated serum TSH levels have been linked to thyroid cancer (2). However, it may not always be reliable, as about 20% of individuals with high-normal TSH levels and negative thyroid antibodies can have thyroiditis. The reference range for TSH varies based on ethnicity and geographic location, with lower limits ranging from 0.2-0.4 mIU/L and upper limits ranging from 2.4-4.2 mIU/L (7).
Due to the limitations of TSH testing, it is essential to consider other biomarkers when diagnosing thyroid disorders. Thyroglobulin antibody (TgAb) is an independent predictor of thyroid cancer, even when TSH falls within a relatively normal range (4).
In patients with hypothyroidism (low-functioning thyroid), serum selenium, zinc, and other trace minerals are often found to be low, while heavy metals like lead may be elevated. These biomarkers could be worth checking (6). Additionally, individuals with celiac disease and intestinal damage often experience hypothyroidism (2-8%), and cytokines, such as IL-12, IL-13, and IL-15, are often raised in both celiac disease and autoimmune thyroiditis (5). Therefore, checking these cytokine levels could be informative in suspected thyroid disorders (1).
Integrity damage to the intestinal barrier may play a significant role in the development of thyroid issues, particularly Hashimoto's thyroiditis. Research has shown a correlation between intestinal barrier damage and other autoimmune diseases. Zonulin level testing can be a useful way to identify intestinal barrier damage and detect thyroid disorders (3).
For patients with high zonulin levels, adopting a wheat-free/gluten-free diet is strongly recommended to support intestinal barrier healing. Supplementing with glutamine can also be beneficial. Healing the intestinal barrier enhances nutrient absorption, leading to increased vitamin D and selenium levels, which in turn can improve thyroid health (5). Additionally, if vitamin D levels are low, considering vitamin D supplementation (or spending more time outdoors), along with zinc and selenium supplementation, may be beneficial. The relationship between improved gut health and thyroid health is significant, as it impacts T cell-mediated immune responses (3). The close connection between anti-transglutaminase IgA autoantibodies and thyroid follicles further highlights the interplay between gut and thyroid health (5).
Assessing thyroid function cannot be solely reliant on a single marker, as dysfunction can occur at various points in the thyroid hormone cascade, from hypothalamus and pituitary function to thyroid gland functioning, nutrient adequacy, enzyme function, transport of T4 and T3, and conversion of T4 to T3 inside cells.
References:
1. Ajjan, R. A., Watson, P. F., & Weetman, A. P. (1997). Detection of IL-12, IL-13, and IL-15 messenger ribonucleic acid in the thyroid of patients with autoimmune thyroid disease. The Journal of Clinical Endocrinology and Metabolism, 82(2), 666–669.
2. Haymart, M. R., Repplinger, D. J., Leverson, G. E., Elson, D. F., Sippel, R. S., Jaume, J. C., & Chen, H. (2008). Higher serum thyroid stimulating hormone level in thyroid nodule patients is associated with greater risks of differentiated thyroid cancer and advanced tumor stage. The Journal of clinical endocrinology and metabolism, 93(3), 809–814.
3. Isleyen, Z. S., Yildirim, S., Gundogan, E., Sari, H., Kucuk, S. H., & Atay, A. E. (2022). Serum Zonulin Levels in Patients with Hashimoto’s Thyroiditis/Hashimoto Tiroditli Hastalarda Zonulin Duzeylerinin Incelenmesi. The Medical Journal of Bakirkoy (Bakırkoy Tıp Dergisi), 18(4), 377.
4. Kim, E. S., Lim, D. J., Baek, K. H., Lee, J. M., Kim, M. K., Kwon, H. S., Song, K. H., Kang, M. I., Cha, B. Y., Lee, K. W., & Son, H. Y. (2010). Thyroglobulin antibody is associated with increased cancer risk in thyroid nodules. Thyroid, 20(8), 885.
5. Malandrini, S., Trimboli, P., Guzzaloni, G., Virili, C., & Lucchini, B. (2022). What about TSH and Anti-Thyroid Antibodies in Patients with Autoimmune Thyroiditis and Celiac Disease Using a Gluten-Free Diet? A Systematic Review. Nutrients, 14(8), 1681.
6. Talebi, S., Ghaedi, E., Sadeghi, E., Mohammadi, H., Hadi, A., Clark, C. C. T., & Askari, G. (2020). Trace Element Status and Hypothyroidism: A Systematic Review and Meta-analysis. Biological trace element research, 197(1), 1–14.
7. Spencer, C. A., Hollowell, J. G., Kazarosyan, M., & Braverman, L. E. (2007). National Health and Nutrition Examination Survey III thyroid-stimulating hormone (TSH)-thyroperoxidase antibody relationships demonstrate that TSH upper reference limits may be skewed by occult thyroid dysfunction. The Journal of Clinical Endocrinology and Metabolism, 92(11), 4236–4240.
