Urinary iodine is increased in papillary thyroid carcinoma but is not altered by regional population iodine intake status: a meta-analysis and implications

Abstract

Excessive iodine intake has been associated with increased risk of thyroid cancer (TC) in many studies, but the results have not been consistent. Since it was common knowledge that urinary iodine (UI) is considered a sensitive marker of current iodine intake, we conducted a meta-analysis to clarify the association between high UI and TC. We adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement, and the Cochrane Collaboration. Betweengroup meta-analyses were performed to compare UI between TC patients and the healthy/euthyroid subjects in local residents and benign thyroid nodules (BTN) patients. Then, between-group meta-analyses to compare the incidence rate of iodine excess were also conducted. The 22 case-control studies included in the meta-analyses represented 15,476 participants. It is the first time to clarify that UI was increased in PTC patients, but was not altered by regional population iodine intake status. Compared with BTN patients, PTC patients exhibited both higher UIC and higher odds ratio of iodine excess only in adequate iodine intake status subgroup; UIC, not the odds ratio of iodine excess, was higher in patients with PTC than those with BTN in above requirements iodine intake subgroup. A novel insight is offered that high UI in PTC patients was less influenced by regional population iodine intake status. It is indicted that high iodine intake is not a risk factor for PTC and high urinary iodine is just a specific characteristic of the disease.

Association between Iodine Intake, Thyroid Function, and Papillary Thyroid Cancer: A Case-Control Study

“…Many previous studies have assessed the association between thyroid cancer and UIC, but some studies have focused on the median difference in UIC between cases and controls [ 25 , 26 ]. Although a meta-analysis reported the ORs for PTC relative to normal controls associated with excessive iodine intake [ 27 ], we could not directly compare their results with our study for the following reasons: two studies published in Chinese could not identify the method; for another study, the OR reported in the meta-analysis was not reported in the original article [ 27 ]; and the fourth study used a UIC reference value that differed from World Health Organization (WHO) standards [ 27 ]. In one study the PTC risk associated with an excessive UIC did not differ significantly between cases and controls [ 28 ].…”

Association of Excess Dietary Iodine Intake with Papillary Thyroid Carcinoma

“…The study by Huang et al (34) showed excess urinary iodine concentrations in 44.3% of PTC patients compared to 22.2% of persons without PTC. Results of a few more studies demonstrated that urinary iodine levels in PTC patients were higher than those of healthy individuals (18,25,30).…”

“…This was because the subjects consumed iodine-rich foods (kelp or soup stock) on at least one or more days of the 16 days. Yan et al's (25) study mentioned that high iodine intake is not a risk factor for PTC and that high urinary iodine is just a specific characteristic of this disease. Iodine retention was found in urinary iodine even with a large single dose iodine administration, e.g., oral administration or injection of iodinated contrast (about 30 grams of iodine), and the urinary iodine levels were transiently increased after receiving iodinated contrast and soon reverted back to baseline either in euthyroid subjects or in PTC patients regardless of thyroidectomy operation (26,27).…”

Circ_0004851 regulates the molecular mechanism of miR-296-3p/FGF11 in the influence of high iodine on PTC

“…Another research suggests that high iodine intake could be linked to the growth of PTC rather than its initiation [ 31 ]. A meta-assessment of 22 cross-sectional studies conducted by Yan et al indicates that high iodine intake does not pose a risk for PTC development and that high urinary iodine is a specific characteristic of the disease [ 36 ]. Some studies have identified associations between excessive iodine intake and elevated risks of lymph node metastasis, larger tumors, peritumoral invasion, bilateral tumor location, and extra-thyroidal metastases.…”