Discrepancy in Iodized Salt Coverage between Household Salt and Salt Used in Dining Establishments: Considerations for Iodine Dietary Assessment

Discrepancies in iodized salt coverage rate (ISCR) between household salt and that used in catering establishments may significantly compromise the accuracy of dietary iodine intake assessments. To evaluate this impact, we analyzed data from the 2023 Shanghai Diet and Health Survey, a cross-sectional study involving 2920 adults. Dietary intake was assessed using three 24-hour dietary recalls and a food frequency questionnaire, while condiment intake was collected using the weighed inventory method. Additionally, salt samples from 960 canteens and restaurants were tested to determine the ISCR in dining establishments. Results showed that the ISCR was 85.9% in dining establishments, markedly higher than the 53.3% observed in households. Among employed participants in Shanghai, 51.7%, 56.1%, and 18.7% reported consuming breakfast, lunch, and dinner outside the home at least once during the three-day study period, respectively. The estimated daily iodine intake was 101 μg/day when dining-out salt was assumed to have the same ISCR as household salt, but it increased to 118 μg/day after accounting for the ISCR discrepancy. In conclusion, the rising prevalence of eating out has reshaped residents' dietary habits, rendering traditional household-centric survey methods inadequate for iodine intake estimation in Shanghai. Incorporating ISCR differences between household and dining settings is essential for more accurate dietary iodine assessments.