Iodine status and sources of dietary iodine intake in Kenyan women and children

摘要

In 2009, the Government of Kenya adopted a mandatory iodine standard for all ediblesalt of 30-50 mg/kg with potassium iodate as a required fortificant. To assess the new standard, iodine nutrition measurements were included in the Kenya National Micronutrient Survey (KNMS) in 2011. Spot urine samples were obtained from 951 school-age children (SAC, 5 - 14y of age) and 623 non-pregnant women (NPW, 15 – 49y), together with 625 salt samples from their households. Because salt is the major dietary source of iodine as well as sodium in Kenya, sodium concentrations were measured in the same urine samples. Using the iodine and sodium data, the report introduces a novel regression technique to apportion the urinary iodine concentrations (UIC) in both survey groups to the key sources of iodine intake, namely, naturally present (native) iodine content, iodized salt in processed foods and iodized household salt. The salt iodine (SI) content in Kenya’s households (mean 40.3 mg/kg, SD 19.4 mg/kg) showed high-quality iodized salt supply. The SI content in 94.9% of households was ≥15 mg/kg. Median UIC findings in SAC (208 μg/L) and NPW (167 μg/L) indicated adequate iodine nutrition. Although variations in UIC values existed by age, gender (only in SAC), residence type, household wealth index, and region, median UIC findings were within the accepted optimum range in virtually all sub-categories. The findings do not suggest the need for change in Kenya’s universal salt iodization (USI) strategy or adjustment of the current salt iodine standard. Partitioning of UIC values by dietary sources of iodine intake in each survey group attributed ± 35% to native dietary iodine content, ± 45% to processed food and ± 20% to household salt. The UIC levels from native iodine intake alone (60.8 μg/L and 65.3 μg/L in SAC and NPW, respectively) fell below the threshold for iodine deficiency, which supports the inference that the current USI strategy in Kenya is effective in preventing iodine deficiency. The results from regression analysis indicate that the iodine intakes of SAC and NPW can be explained mainly, and in the same way, by their urinary sodium concentrations (UNaC) and the SI contents in salt from their households. The spot UNaC data do not accurately represent salt intake estimates but the mean UNaC findings may be useful for analyzing future changes in salt supply and use from efforts to reduce the salt intake of Kenya’s population.