Iodized salt and child growth: Isolating causality and implications for government policy in India

Background: Iodine deficiency disorders (IDD) are one of the most common causes of preventable mental and physical retardation. In India, despite efforts to combat IDD through the Universal Salt Iodization program, the use of iodized salt nationwide was still only 51% in 2005. Moving forward, it is important to establish a causal link between access to iodized salt and child health, in order to assess the effectiveness of current government policy and make recommendations for the future. Methods: This paper examines household salt iodine concentration and anthropometric outcomes of over 18,000 children from the 1998 India National Family Health Survey. To determine causality, the analysis utilizes two-stage least squares (TSLS) regressions with state-fixed-effects. The instruments, collected from the Geographic Information Systems, include precipitation, elevation, distance to coast, and distance to salt-transporting railroads. Results: On average children in India ages 0-5 years old were borderline stunted at 1.91 standard deviations below the 1997 U.S. National Center for Health Statistics (NCHS) standard. The TSLS estimate revealed that having salt with an iodine content of 30ppm (as opposed to 0, 7 or 15ppm) led to a 2.55 standard deviation increase in height-for-age outcome (p<0.05). This outcome was more pronounced in girls and in rural settings. Conclusions: By establishing causality between access to iodized salt and childhood physical growth, this paper shows that the government's efforts to eliminate iodine deficiency through a salt iodization program are worthwhile. However, targeting certain populations increasing the recommended intake from 15ppm to 30ppm may strengthen its impact.