Until 1998, iodine deficiency was a public health problem in the Philippines. A law entitled “An Act Promoting Salt Iodization Nationwide” (ASIN) has been passed and implemented by the government to eliminate iodine deficiency. The contribution of salt iodization, as well as dietary, health, and environmental factors, to improving the intellectual performance of Filipino schoolchildren remains to be determined.

The objectives of the study were to determine the relationship between iodine status and levels of psychomotor and cognitive performance in first-grade children aged 6 to 10 years, and to examine the extent to which dietary, biochemical, health, and environmental factors contribute to children's mental performance.

Two hundred ninety children in six classroom sections from a public school in Manila were examined by measurement of urinary iodine excretion (UIE) and thyroid palpation. The median UIE level for each section was determined. Sixty-five children classified as iodine deficient (UIE < 90 μg/L with grade 1 goiter, n = 34) and non-iodine deficient (UIE > 100 μg/L without goiter, n = 31) were given psychomotor and cognitive function tests (Bender–Gestalt and Raven's Colored Progressive Matrices). Scores from the two tests were used to determine each child's general ability percentile rank. Other variables examined were dietary intake (% RDA of nutrients ingested based on two nonconsecutive 24-hour recalls); deficiencies in iron, vitamin A, and selenium; parasitic infection; coliform contamination of drinking water; household use of iodized salt; illness in the past 2 weeks; and wasting and stunting.

Children whose general ability scores were at or above the 50th percentile had higher UIE levels, but the relationship was not significant. Children from sections with higher median UIE levels had higher percentile ranks for general ability (p =.002). Backward logistic regression showed that the variance in deficient and adequate mental performance was explained by dietary intakes that met ≥ 80% of the RDA for energy, protein, thiamin, and riboflavin; the use of iodized salt; child's iodine status; and stunting (R² =.520, p =.0016). Higher class median UIE was associated with better psychomotor and cognitive performance in children who were tested. Factors that contributed to better performance include higher intakes of energy, protein, thiamin, and riboflavin; household use of iodized salt; normal iodine status; and absence of stunting or chronic malnutrition.

Salt iodization, accompanied by adequate intakes of energy, protein, and foods rich in thiamin and riboflavin, can contribute to improved mental performance in Filipino schoolchildren. Longer-term factors that can contribute to improved performance are achievement of normal iodine status and elimination of protein–energy malnutrition.