The data from Africa very strongly suggests height did not improve over past 50 years. There are a number of sources. Here is a good NYTimes summary.
The average height of European males increased by an unprecedented 11 cm between the mid-nineteenth century and 1980, according to a new paper published online today in the journal Oxford Economic Papers. Contrary to expectations, the study also reveals that average height actually accelerated in the period spanning the two World Wars and the Great Depression.