Abstract
Background: Iodised discretionary salt has been used as a method to improve the iodine status of the New Zealand population since 1939. Discretionary salt intake is estimated to be between 10-15% of total sodium intake however the contribution of iodised discretionary salt to total iodine intake is not known. Reliable methods for determining iodised discretionary salt are required to accurately assess the iodine intake of New Zealand adults.
Objective: The aim of this study was to determine the feasibility of a lithium-tagged salt method to determine the quantity of discretionary iodised salt consumed in the diet of adults living in Dunedin and its contribution to iodine intakes.
Design: This observational study was conducted between September and October 2016 in 15 adults aged between 18 and 70 years living in Dunedin. Participants were asked to complete a weighed diet record and 24-hour urine collection for six days over a nine day period. Baseline data were collected on Days 1 and 2. On Day three, participants were asked to use lithium-tagged salt without changing usual salt intakes. Urinary and dietary methods were used to determine discretionary salt.
Results: The estimated mean total sodium intake derived from urinary analysis over all intervention days was 2900mg/day (equivalent to 7.3g salt). Using the lithium-tagged salt method, the mean discretionary sodium intake was 14% of this mean total sodium intake. From the weighed dietary records, mean total sodium intake was 2878mg/day (i.e. 7.3g salt) of which 25% was from discretionary salt. Using the lithium-tagged salt method, the total iodine intake was 157µg/day, of which 59µg/day (38%) came from discretionary salt. Using the weighed dietary record method, the total iodine intake was 173µg/day, of which 82µg/day (47%) came from discretionary salt.
Conclusion: In contrast to weighed dietary records, the lithium-tagged salt method resulted in the estimation of a lower proportion of total iodine that contributed to discretionary salt. However both methods showed that discretionary iodised salt use was a significant contributor to iodine intakes in this study sample, however a larger, more representative sample of the New Zealand population is needed to assess the contribution of iodised salt to the diet of the wider New Zealand population.