Correlation between adult iodine nutrition and thyroid nodules

Abstract

Objective To investigate urinary iodine and dietary iodine intake in adults, and to analyze the relationship of urinary iodine and daily dietary iodine intakes with thyroid nodules. Methods Totally 30 participants with nutritional background were enrolled prospectively from January to March 2015 in Shanghai. The 3-day survey of 24-hour's diet record was made using weighting method to evaluate the daily nutrient intakes. On the second and third days of dietary records, urine samples in fasting status and 2 hours after meals were collected from all the participants (n=240). The levels of urine iodine were measured, and dietary iodine intake calculated. 3-month food frequency questionnaire was completed and thyroid ultrasonography performed. Results The median urinary iodine (MUI) of fasting and 2 h postprandial urine samples was 137.56 μg/L(91.4-211.5 μg/L). The portions of participants with iodine insufficiency, iodine adequate, and iodine above requirements or excess were 20.2%, 56.7%, and 23.3%, respectively. Inter-individual MUI varied from 36.31 μg/L to 359.20 μg/L. No significant difference was found between the fasting urinary iodine and 2 h postprandial urinary iodine (P=0.389). The average dietary iodine intake was (197.2±74.2)μg/d, and the proportions from iodine salt and drinking water were 70.2% and 5.4%, respectively. There was a significant positive correlation between dietary iodine intake and urinary iodine value of the same day (r=0.426, P=0.019). Participants with thyroid nodules had higher urinary iodine than participants without thyroid nodules [(194.0±101.5)μg/L vs. (135.7±72.9)μg/L, P<0.001]. Conclusions Inter-individual iodine nutritional status are significantly different under natural living status. Increased urinary iodine may be related with thyroid nodules. Repeat random urine iodine test combined dietary assessment may reduce the error in evaluating individual iodine nutritional status. Key words: Iodine; Nutrition assessment; Thyroid nodule