I'll see if I can still find it on my computer, but I recall reading, some years ago, an article about the comparative heights of Americans and Europeans from the American Revolutionary War to today. Essentially, the Americans had a head start over their European counterparts (a fact remarked upon by German officers at Saratoga and elsewhere), which increased slightly during the Industrial Revolution, as Europeans became more urbanised and their diet deteriorated, but then completely disappeared in the later 20th Century (to the point where it has now been reversed), when free healthcare became the norm in Europe, and the urban poor became more numerous in the US.