Median UIC of the adult population in the city of Sadra was 175 µg/L, which categorizes the iodine status of the population as adequate based on WHO guidelines. The results found in our study is significantly higher than 70 µg/L found in adults (72.9 and 68.9 µg/L in men and women respectively) and the 87.3 µg/L in the pregnant population of Tehran. [7, 8] Median UIC in this study is similar to median UIC of 200 µg/L and 186.1 µg/L in 8–10 year old school-children of Shiraz (capital of Fars province) and Iran respectively.  Median UIC in adults worldwide includes 144 µg/L in China , 110 µg/L in US , 46 µg/L in Italy  and 124.66 µg/L in Spain . Results from our study indicated that national efforts to curb iodine deficiency is still successful 28 years after the introduction of 1994 Salt Iodization Act.
Despite worldwide efforts to combat iodine deficiency, many countries have experienced decreased median UIC levels while some have experienced iodine insufficiency resurgence. Median UIC has decreased from 133 µg/L in 2010 to 110 µg/L in US women of reproductive age and from 320 µg/L in US general population in 1974 to 133 µg/L in the same population in 2013.  Previously iodine sufficient countries such as Norway, Finland and Germany have been categorized as iodine insufficient based on the latest IGN report.  Iodine insufficiency has also reoccurred in the past in countries such as France, Australia and UK due to dietary changes. [1, 15, 16] In some countries such as Columbia and Argentina decrease in UIC levels has been attributed to lack of proper iodine status monitoring and public health strategies. [8, 17–20]
In Iran, studies have also shown reduction in UIC levels. Median UIC in adults of Tehran has dropped from 232 µg/L (1996) to 100 µg/L (2010).  Similar results have also been found in Tehranian pregnant women (186 µg/L in 1998 to 87.3 µg/L in 2014) and in Iranian school children (205 µg/L in 1996 to 161 µg/L in 2013). [7, 21–22] Nazeri et al believe that the reduction in salt consumption in Iran can be an attributable factor.  Indeed, salt intake per person in Tehran has dropped from 10 gr per day (2000) to 8.4 gr per day (2009) with similar results seen in Yazd and Isfahan. [8, 23] In Shiraz, Babaali et al found that daily consumption of salt in Shiraz was 7.1 gr.  In our study, we found a much higher median of 9.59 gr salt consumed per day in Sadra adults. This number is much closer to the results found in 2000 Tehran adults. The higher use of Salt in Sadra can be a contributing factor to its higher UIC levels.
In our study, we found no significant difference in iodine levels between genders. Similar results were found by Nazeri et al.  However, in studies by Iacone et al and Tayie et al, men had higher UIC levels. [25, 26] We found a significant negative correlation between hypertension and UIC levels. Similar results were found by Usha Menon et al.  Meanwhile, Tayie et al found no correlation between those factors, while Liu J et al found a positive correlation between UIC levels and high blood pressures.  Also, we found that better education levels were associated with significantly higher UIC levels. Similar results were found in Tehran by Nazeri et al when using univariate logistic regression. However, this statistical significance was diminished when adjusting for household salt iodine content and daily salt intake, suggesting that these factors were interconnected when leading to lower UIC levels.  Based on these results, we hypothesize that subjects with higher education levels are more likely to use iodized salt.
In our study, we found a positive correlation between TSH and UIC levels and a negative correlation between T4 and UIC levels, which is in contrast to the negative correlation seen between these two factors especially in iodine deficient areas.  Some previous studies showed no direct association between UIC and serum TSH or T4.  Some the other such as NHANES III found that higher urinary iodine excretion was significantly related to higher TSH concentration.  Although in our study, individuals with higher level of urinary iodine excretion had higher TSH and lower T4 levels, these concentrations were within the physiologic range. It seems that distribution of TSH shifted toward the right in iodine sufficient area could be affected by the hereditary and genetic influences on the set-point of thyroid hormone. 
During food preparation, some methods such as heating and washing can decrease the amount of salt iodine content. Microwaving, boiling, rice washing and poor salt preservation conditions including storage in sunlight can decrease the effective iodine content.  The WHO expects approximately 20% salt iodine loss from retail until food served at table.  Despite this, in our study we found no significant difference in UIC between subjects storing salt in the dark and those storing in direct sunlight. In addition, there was also no difference in UIC between those that add salt before food preparation, those that add salt during food preparation and those that add salt after the food is fully prepared.
We found no significant correlation between daily salt intake per person and UIC levels. However, we found a significant positive correlation between UIC and urine sodium content, which is more accurate method of measuring salt consumption. [34, 35] Similar results were found by Nazeri et al. These results along with results from other studies [8, 36–37] and the WHO declaration illustrate the link between salt consumption and iodine status. This can also further link the higher UIC levels found in Sadra city and the city’s higher use of salt consumption in comparison to the results from Tehran.
In this study, we found a negative correlation between thyroid volume and UIC. Iodine deficiency has goitrogenic effect and this negative correlation is anticipated. Some previous studies explained that association between iodine status and thyroid volume is inconsistent; and have reported that there is no correlation between thyroid volume and UIC in iodine sufficient areas. [38, 39] It seems that volume of thyroid gland is population-specific and some genetic and environmental factors contribute to thyroid volume variation especially in iodine sufficient areas.