Association between Serum Free Thyroxine and Anemia in Euthyroid Adults: A Nationwide Study (Endocrinol Metab 2020;35:106-14, Mijin Kim et al.)

Zheng Feei Ma

doi:10.3803/EnM.2020.35.2.484

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Letter Association between Serum Free Thyroxine and Anemia in Euthyroid Adults: A Nationwide Study (Endocrinol Metab 2020;35:106-14, Mijin Kim et al.): Zheng Feei Ma^1,2; Endocrinology and Metabolism 2020;35(2):484-485.
DOI: https://doi.org/10.3803/EnM.2020.35.2.484
Published online: June 30, 2020

¹Department of Health and Environmental Sciences, Xi’an Jiaotong-Liverpool University, Suzhou, China

²School of Medical Sciences, Universiti Sains Malaysia, Kota Bharu, Malaysia

Corresponding author: Zheng Feei Ma. Department of Health and Environmental Sciences, Xi’an Jiaotong-Liverpool University, Suzhou 215123, China, Tel: +86-512-8188-4938, Fax: +86-512-8188-4938, E-mail: Zhengfeei.Ma@xjtlu.edu.cn

• Received: May 6, 2020 • Accepted: May 11, 2020

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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See the reply "Association between Serum Free Thyroxine and Anemia in Euthyroid Adults: A Nationwide Study (Endocrinol Metab 2020;35:106-14, Mijin Kim et al.)" in Volume 35 on page 669.

See the article "Association between Serum Free Thyroxine and Anemia in Euthyroid Adults: A Nationwide Study" on page 106.

This letter is regarding the recent article “Association between serum free thyroxine and anemia in euthyroid adults: a nationwide study” by Kim et al. [1]. The findings presented by the authors are both interesting and applicable to clinicians and researchers who are currently working in this field. The authors reported that low free thyroxine (fT4) levels were associated with lower hemoglobin (Hb) levels and an increased risk of anemia in euthyroid Korean adults in a nationwide cross-sectional study [1].

Although the study had a large sample size of 5,352 adults, it had some important limitations that were not acknowledged by the authors. First, all the biochemical parameters—including thyroid-stimulating hormone (TSH), fT4, and Hb—were only measured once. Instead, it has been suggested that such measurements should be repeated to avoid underestimating the observed relationship between fT4 and anemia, especially in euthyroid participants. In addition, the authors did not apply age- and sex-specific reference ranges for TSH and fT4 levels in their analysis. This is particularly important because Korea is considered an iodine-replete area, and more than adequate and/or excessive iodine levels have been reported in Koreans [2,3]. An important cause of anemia is iron deficiency, as iron-deficiency anemia is one of the most common nutrient deficiencies worldwide. Understanding the causes of anemia at the population level is crucial for planning public health interventions to reduce its prevalence. Future studies should also consider investigating how different forms of anemia can affect thyroid function in both sexes according to age. In addition, adults diagnosed with anemia are more likely than their counterparts without anemia to have lower economic productivity and a reduced quality of life. Therefore, the adverse consequences of anemia should not be overlooked.

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References

1. Kim M, Kim BH, Lee H, Jang MH, Kim JM, Kim EH, et al. Association between serum free thyroxine and anemia in euthyroid adults: a nationwide study. Endocrinol Metab (Seoul) 2020;35:106–14.Article PubMed PMC
2. Pearce EN. Iodine deficiency disorders and their elimination; Cham: Springer International Publishing; 2017. Chapter 2:Assessment of population iodine status. p. 15–28.
3. Park SY, Kim HI, Oh HK, Kim TH, Jang HW, Chung JH, et al. Age- and gender-specific reference intervals of TSH and free T4 in an iodine-replete area: data from Korean National Health and Nutrition Examination Survey IV (2013–2015). PLoS One 2018;13:e0190738.Article PubMed PMC

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Maternal iron deficiency assessed by serum ferritin and birth outcomes in mainland China
Hang Zhou, Yiming Lu, Jianying Luo, Binyu Pan, Qihua Zhao, Min Chen, Zheng Feei Ma
Scientific Reports.2025;[Epub] CrossRef

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Association between Serum Free Thyroxine and Anemia in Euthyroid Adults: A Nationwide Study (Endocrinol Metab 2020;35:106-14, Mijin Kim et al.)

Endocrinol Metab. 2020;35(2):484-485. Published online June 24, 2020

DOI: https://doi.org/10.3803/EnM.2020.35.2.484

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Association between Serum Free Thyroxine and Anemia in Euthyroid Adults: A Nationwide Study (Endocrinol Metab 2020;35:106-14, Mijin Kim et al.)