Studies have shown that individuals deficient in micronutrients have significant difficulty developing cognitive ability, and this correlates to lower scores on IQ tests. For example, one study showed that individuals who were deficient in iodine scored on average 12 points less on IQ tests. (2) Considering the average IQ test score is 100, a 12 point drop is quite substantial, and shows that just one micronutrient deficiency can cause a significant decrease in test scores.