Iodine deficiency and schooling attainment in Tanzania

An estimated one billion people globally are at risk of iodine deficiency disorder (IDD), the only micronutrient deficiency known to have significant, non-reversible effects on cognitive development. This research evaluates the impact of reductions in fetal IDD on child schooling attainment in Tanzania that resulted from an intensive distribution of iodized oil capsules (IOC) in several districts of the country between 1986 and 1994. We look for evidence of improvements in cognitive ability attributable to the intervention by assessing whether children who benefited from iodine supplements in utero exhibit higher rates of grade progression at ages 10 to 13. Our findings suggest that reducing fetal IDD has significant benefits for child cognition: Children who receive iodine in utero attain an average of 0.36 years of education above siblings and older and younger children in their district. Furthermore, the effects appear to be substantially larger for girls, consistent with new evidence from laboratory studies in animals indicating greater cognitive sensitivity of the female fetus to in utero iodine deprivation, including sex-specific responses to maternal thyroid hormone restriction on genetic expression of neural thyroid hormone receptors. The results are consistent across household and district fixed effects models and patterns of variation in estimated effects are consistent with predictions regarding the relative vulnerability of specific subpopulations to fetal IDD. Cross-country regression estimates indicate a strong negative influence of total goiter rate and strong positive influence of salt iodization on female school participation. These findings provide micro-level evidence of the direct influence of ecological conditions on economic development, in addition to suggesting a potentially important role of IDD in explaining global patterns of gender differences in schooling. † We thank Lisa Vura-Weis and Sonali Murarka for excellent research assistance. We are also grateful for feedback and discussion from seminar participants at Harvard, Princeton and the University of Michigan, and 2006 SITE conference participants. Please direct correspondence to [email protected].