The influence of iodine deficiency on the cognitive performance of school children in Saki, South-West Nigeria

Abstract

The influence of inadequate iodine intake on the thyroid status and cognitive performance of school children in Saki, a town within the goitre belt of South-western Nigeria with known environmental iodine deficiency, was assessed. One hundred and ninety-seven (197) study subjects from Saki and seventy (70) appropriately matched control subjects from Moniya, near Ibadan, the Oyo State capital were recruited into the study. The subjects were apparently healthy primary school pupils between the ages of 10 and 14 years and had been resident in the respective locality for at least two (2) years. After establishing the presence of goitre, blood was collected for thyroid function tests by venepuncture from each pupil. The cognitive function tests, Draw-A-Person (DAP) test and the Standard Progressive Matrices (SPM) were administered simultaneously to all the pupils in the class. Urine samples were collected for urinary iodine estimation The mean urinary iodine concentration was significantly lower in Saki than in Moniya (134.81 ± 69.86 vs 220.00 ± 69.00 ug/L, P < 0.01). The total goitre rates (TGR) and the visible goitre rates (VGR) were 15.2% and 1.5% for Saki, and 8.6% and 4.3% for Moniya, respectively. The mean plasma total T4 was significantly lower in Saki pupils (97.55 ± 26.64 nmol/L vs 122.52 ± 26.51 nmol/L P < 0.05). The TSH level was higher in Saki pupils than in Moniya pupils (4.72 ± 1.38 mU/L vs 4.26 ± 1.28 mU/L), but the difference was not statistically significant. Scores on intelligence function tests (DAI5 and SPM) were lower for Saki pupils when compared with Moniya pupils, though the differences were not statistically significant. These results show that there is a mild but significant iodine deficiency disorder problem in Saki. However, the children in Saki still maintained euthyroidism and the mild degree of iodine deficiency did not seem to have adversely affected their cognitive performance.