How did schooling laws improve long-term health and lower mortality?

"Although it is well known that there is a strong association between education and health much less is known about how these factors are connected, and whether the relationship is causal. Lleras-Muney (2005) provides perhaps the strongest evidence that education has a causal effect on health. Using state compulsory school laws as instruments, Lleras-Muney finds large effects of education on mortality. We revisit these results, noting they are not robust to state time trends, even when the sample is vastly expanded and a coding error rectified. We employ a dataset containing a broad array of health outcomes and find that when using the same instruments, the pattern of effects for specific health conditions appears to depart markedly from prominent theories of how education should affect health. We also find suggestive evidence that vaccination against smallpox for school age children may account for some of the improvement in health and its association with education. This raises concerns about using compulsory schooling laws to identify the causal effects of education on health"--Federal Reserve Bank of Chicago web site.