Relationship of serum iron and thyroid hormone in obesity and after laparoscopic sleeve gastrectomy.

Background: Iron is an essential element for thyroid function. However, no study focuses on the association between iron and thyroid in individuals with obesity. Our research aimed to investigate the iron status in relation to baseline thyroid hormone levels and after laparoscopic sleeve gastrectomy (LSG).

Methods: A total of 216 subjects with obesity were enrolled and divided into low and high iron groups depending on the median value. The association between iron and thyroid hormone was analyzed and compared before and after LSG at the 6-month follow-up in patients who underwent LSG.

Results: 1) In all, Total Triiodothyronine (TT3) was significantly higher in high iron than low iron group (P = 0.008). TT3 and thyroid stimulating hormone (TSH) were significantly higher in high iron than low iron group (1.92 ± 0.61 vs. 1.69 ± 0.28 nmol/l, P = 0.029; 2.93 ± 1.66 vs. 1.88 ± 1.03 mU/l, P = 0.002) in females while not in males (all P > 0.05). 2) Iron was significantly positively associated with free triiodothyronine (FT3), free thyroxine (FT4), TT3 and TSH (all P < 0.05). Adjusted for body mass index (BMI), total cholesterol (TCH), high-density lipoprotein cholesterol (HDL-C), fasting insulin (FINS) and homeostatic model assessment of insulin resistance (HOMA-IR), FT3, FT4 and TSH were still significantly associated with iron (all P < 0.05). 3). Regression analysis showed that iron was significantly associated with FT4 (β = 0.338, P = 0.038). 3) LSG led to decreased FT3, FT3, TT3, total thyroxine (TT4) and TSH at 6 months follow-up (all P < 0.05). Changed FT4 was significantly associated with changed iron (r = 0.520, P = 0.009). Subjects with iron decreased had more significant decreased TT4 than subjects without iron decreased (P = 0.021).

Conclusion: Serum iron overload is significantly associated with impaired thyroid function in subjects with obesity. LSG led to improved thyroid function which is associated with a change in iron.

Trial registration: NCT04548232 registration date is on October 9, 2022, registered in https://register.

Clinicaltrials: gov/ .