Conclusion. We conjecture that the U.S. health-care system, as well as the relatively weak welfare safety net, might be why human growth in the United States has not performed as well in relative terms as one would expect on the basis of income alone. The comparative pattern bears some similarly to that of life expectancy insofar as the United States is also lagging behind in that respect.

Update: Added "Relative" to title

A few years ago I saw a study on the world's "tallest nations". The Dutch were the tallest on the list, and the reasons given included wealth, great health care, and a diet high in dairy.