Abstract
Background
Iodine deficiency has serious consequences, and the Universal Salt Iodization initiative has attempted to reduce the extent of deficiency.
Objective
We aim to see how far across-country variations in urinary iodine in school-age children can be explained by environmental factors, particularly soil iodine and the availability of iodized salt.
Methods
We use simple multivariate regression for two separate datasets, one for 30 developing countries, and one for 13 developed countries, using data on availability of iodized salt and soil iodine levels.
Results
Median urinary iodine excretion is significantly and positively related to household availability of iodized salt (elasticity, 0.73) for developing countries, but the soil coefficient is not significant, probably because the dummy variable is not well measured. For the developed countries, there is a positive and significant effect of salt penetration rates (elasticity, 0.83) and a positive and significant effect of soil iodine (elasticity, 0.77). There is also a suggestion that countries with more serious soil deficits are more likely to iodize salt, so that univariate regressions of urinary iodine excretion on salt availability or penetration rates underestimate the beneficial effects of iodized salt availability on iodine nutrition.
Conclusions
There are limitations to cross-sectional (ecologic) studies such as this, and the data are not perfect. Nevertheless, the results provide support for policies to iodize salt, given the widespread deficiency of iodine in diets worldwide.