Objective: To explore the iodine level in the environment and the iodine status among the general population as well as the prevalence of thyroid nodules in Hangzhou city. Relationship between the prevalence of thyroid nodules and the policy of universal salt iodization in Hangzhou was also analyzed.
Methods: Questionnaire, a 3-day weighed dietary record method, and 3 days' 24-hour dietary recall method were used to understand the iodine nutrition status and dietary intake of iodine among the general population in the city. Drinking water, edible salt and morning urine were collected to determine iodine content. All objects under survey underwent the thyroid B ultrasonic examination. Statistical analysis was done by SPSS 13.0 and SAS 9.1.
Results: (1) In total, 12 620 effective questionnaires were available, with 221 water samples, 12 730 urine samples, and 3593 salt samples collected. 12 515 objects underwent B ultrasonic examination, and 1848 received dietary investigation. (2) Water iodine level of Hangzhou was in the range of 0.20 - 5.99 µg/L, with the median level as 2.58 µg/L. (3) Average daily dietary intake of iodine for adult males in Hangzhou was 289.2 µg/d. The contribution of iodine intake from iodized salt was 74.4%. (4) The median of Hangzhou residents' urinary iodine was 178.80 µg/L, with the urinary iodine levels at 100 µg/L-, 200 µg/L-, < 100 µg/L, and ≥ 300 µg/L groups were 37.14%, 23.11%, 21.05%, and 18.69% respectively. Urinary iodine of pregnant women was 141.0 µg/L. (5) Incidence of thyroid nodules in females (28.6%) was higher than that of males (20.1%). The detection rate increased with age (6.4% at group 6-, 10.9% at 12-, 12.0% at 18-, 24.4% at 40-, and 38.8% at 65-); with the highest in urban area (29.8%), followed by suburbs (23.3%) and in rural area it showed the least (20.3%). Urinary iodine level was found lower among the population who had been detected with thyroid nodules (160.36 µg/L) than those among the undetected population (182.00 µg/L).
Conclusion: Hangzhou appeared to be an area where the environmental was iodine deficient. Iodized salt was the major source of iodine intake. The iodine status among the general population seemed to be safe and suitable, but the iodine level for pregnant women was not sufficient. There was still no evidence indicating that the universal salt iodization policy in Hangzhou was associated with the prevalence of thyroid nodules.