To determine iodine levels in salt and iodine deficiency prevalence in school-aged children in 16 districts in Tanzania with previous severe iodine deficiency.

A cross-sectional study in schoolchildren. Systematic probability sampling was used to select schools and subjects for goitre assessment and urinary iodine determination.

Sixteen districts randomly selected from the 27 categorised as severely iodine-deficient in Tanzania.

The study population was primary-school children aged 6–18 years who were examined for goitre prevalence and urinary iodine concentration (UIC). Salt samples from schoolchildren's homes and from shops were tested for iodine content.

The study revealed that 83.3% of households (n = 21 160) in the surveyed districts used iodised salt. Also, 94% of sampled shops (n = 397) sold iodised salt, with a median iodine level of 37.0 ppm (range 4.2–240 ppm). Median UIC in 2089 schoolchildren was 235.0 μg l− 1 and 9.3% had UIC values below 50 μg l− 1. The overall unweighted mean visible and total goitre prevalence was 6.7% and 24.3%, respectively (n = 16 222). The age group 6–12 years had the lowest goitre prevalence (3.6% visible and 18.0% total goitre, n = 7147). The total goitre prevalence had decreased significantly in all districts from an unweighted mean of 65.4% in the 1980s to 24.3% in 1999 (P < 0.05). We believe this difference was also biologically significant.

These findings indicate that iodine deficiency is largely eliminated in the 16 districts categorised as severely iodine-deficient in Tanzania, and that the iodine content of salt purchased from shops is highly variable.

Northern rural areas of Tehran have been shown to have severe iodine deficiency in our previous studies. In 1989 the inhabitants of these villages received an injection of iodised oil, followed by iodised salt distribution in 1993. The aim of the present study was to evaluate the effect of the iodine supplementation on iodine-deficient schoolchildren with hypothyroidism in these villages.

In total, 571 students aged 6–14 years were studied. Goitre was graded according to the World Health Organization classification. Serum concentrations of thyroid hormones (thyroxine (T4) and triiodothyronine (T3)) and thyroid-stimulating hormone (TSH) were determined using commercial kits, and urinary iodine was measured using a digestion method. The results were compared with data from our previous study in 1989.

Total goitre rate decreased by 42% in 1999 compared with that in 1989. A significant decrease in Grade 2 goitre concomitant with an increase in Grade 1 goitre was seen (P < 0.001). Values of the variables studied before (1989) and 10 years after iodine supplementation (1999) were: median urinary iodine excretion, 2.0 vs. 19.0 μg dl−1 (P < 0.001); T4, 6.5 ± 2.0 vs. 8.4 ± 1.6 μg dl−1 (P < 0.001); T3, 177 ± 38.0 vs. 145 ± 29.0 ng dl−1 (P < 0.001); TSH, 10.8 ± 15.1 vs. 1.8 ± 0.8 μU ml−1 (P < 0.001). No correlation was found between thyroid hormones and TSH on the one hand, and goitre and urinary iodine, on the other. Serum T4, T3 and TSH concentrations were within normal ranges in all schoolchildren in 1999.

This study showed that euthyroidism induced by administration of iodised oil in iodine-deficient schoolchildren with hypothyroidism is sustained following the consumption of iodised salt.