When Kim Sung-Il died in 1994 and was replaced by Kim Jong-Il, there was a period of paralysis in government, poor harvests, terrible technology, highly inefficient and completely state-run agriculture and industry. It was a perfect storm that people say caused the deaths of 1-1.5m people.
Since 1998, people have been fed but the diet is very poor - low in meat, poor quality grain, no fruit and sporadic famine. So their calorie intake must be very low and it's no surprise they have stunted growth. You don't see a fat North Korean except their leader.
There has been no industrialisation so there are nearly medieval agricultural conditions, very low in fertiliser and very low productivity because people are so weak. It's a vicious circle and no trade with the outside world to bring food in.
In the 1990s North Korea suffered a terrible famine. Today, according to the World Food Programme, "one in every three children remains chronically malnourished or 'stunted', meaning they are too short for their age".
South Korea, in contrast, has experienced rapid economic growth. Bloem says "economic growth is one of the main determinants of height improvement".
So while North Koreans have been getting shorter, South Koreans have been getting taller.
Farm in North Korea
"If you look at older Koreans," says Schwekendiek, "we now see a situation where the average South Korean woman is approaching the height of the average North Korean man.
"This is to my knowledge a unique situation, where women become taller than men."
The secretive nature of North Korea makes it difficult to find reliable data for analysis.
Schwekendiek has studied refugees, but he rejects the notion that people driven to cross the border to South Korea are the most disadvantaged and therefore most likely to be stunted.
The refugees, he says, "come from all social strata and from all regions".
He has also studied data collected by the North Korean government and by international organisations working in North Korea, which he says support his findings.
It seems that this height statistic reveals a tragic fact - that as South Koreans have got richer and taller, North Korean children are being stunted by malnourishment.