Post-Graduation Program-Medical Sciences, Santa Casa de Porto Alegre, Department of Endocrinology, Universidade Federal de Ciências da Saúde de Porto Alegre, Porto Alegre-RS, Brazil.
Thyroid. 2011 Jan;21(1):61-7. doi: 10.1089/thy.2010.0232. Epub 2010 Dec 16.
The importance of restricting iodine intake to increase thyroid uptake of ¹³¹I is well-known, but its minimum duration is not clear. The present study aimed at determining whether 3 weeks is superior to 2 weeks for a low-iodine diet (LID) as a means of increasing the thyroid uptake of ¹³¹I and reducing urinary iodine. A second goal was to evaluate the effectiveness of a questionnaire about ingestion and exposure to iodine to predict individuals in whom the LID would be less effective.
Forty-six outpatients who came to the Nuclear Medicine Unit of Santa Casa de Porto Alegre, Brazil, for thyroid evaluation, were randomized to receive an LID for 2 or 3 weeks. Questionnaires regarding their exposure to iodine, the thyroid uptake of ¹³¹I, and the iodine and iodine/creatinine ratio in urine samples were administered or obtained at the beginning and end of the diet.
The questionnaire indicated exposure to exogenous iodine in five patients during their LID, all in the 3-week group. Their thyroid ¹³¹I uptake was significantly lower than patients who did not give a history of iodine exposure (p = 0.016). The comparative analysis between the 2-week and 3-week diet groups was then performed excluding the five contaminated patients. The ¹³¹I uptake increased by 43% in the 2-week group and 26.7% in the 3-week group (p = 0.105). Both diets for 2 and 3 weeks caused significant decrease in urinary iodine (p < 0.001), without a difference between the groups (63.2% in the 2-week group and 60.9% in the 3-week group, p = 0.955). There was no difference in the percentage of patients with urinary iodine ≤100 μg/L (p = 0.25) and urinary iodine ≤50 μg/L (p = 0.86) between the groups. A correlation between urinary iodine and iodine/creatinine ratio (r = 0.516; p < 0.001) was observed.
Two weeks of an LID are probably sufficient to augment thyroid uptake of ¹³¹I, with little or no benefit from longer periods of an LID. Questionnaires regarding exposure to iodine similar to those employed here should identify individuals in whom the LID has not been as effective in increasing the thyroid uptake of ¹³¹I.
限制碘摄入以增加甲状腺对 ¹³¹I 的摄取量的重要性是众所周知的，但具体的最短持续时间尚不清楚。本研究旨在确定低碘饮食（LID）作为增加 ¹³¹I 甲状腺摄取量和减少尿碘的手段，3 周是否优于 2 周。第二个目标是评估关于摄入和暴露于碘的问卷是否可以预测 LID 效果不佳的个体。
46 名因甲状腺评估而前往巴西南卡西亚德波图阿雷格核医学科就诊的门诊患者被随机分配接受 2 周或 3 周的 LID。在饮食开始和结束时，他们接受或获得了关于其碘暴露、¹³¹I 甲状腺摄取以及尿样中碘和碘/肌酐比值的问卷。
问卷显示，在 LID 期间，3 周组中有 5 名患者有外源性碘暴露史。他们的甲状腺 ¹³¹I 摄取明显低于没有碘暴露史的患者（p=0.016）。然后排除 5 名受污染的患者，对 2 周和 3 周饮食组进行了比较分析。2 周组的 ¹³¹I 摄取增加了 43%，3 周组增加了 26.7%（p=0.105）。两种 2 周和 3 周的饮食都显著降低了尿碘（p<0.001），但两组之间没有差异（2 周组为 63.2%，3 周组为 60.9%，p=0.955）。两组中尿碘≤100μg/L（p=0.25）和尿碘≤50μg/L（p=0.86）的患者百分比无差异。尿碘与碘/肌酐比值之间存在相关性（r=0.516；p<0.001）。
2 周的 LID 可能足以增加甲状腺对 ¹³¹I 的摄取，而较长时间的 LID 则几乎没有或没有益处。类似于此处使用的问卷来询问关于碘暴露的问题，应能够识别出 LID 对增加 ¹³¹I 甲状腺摄取量效果不佳的个体。
