https://www.bbc.co.uk/news/magazine-17774210

Professor Daniel Schwekendiek from Sungkyunkwan University in Seoul has studied the heights of North Korean refugees measured when they crossed the border into South Korea.

He says North Korean men are, on average, between 3 - 8cm (1.2 - 3.1in) shorter than their South Korean counterparts.

A difference is also obvious between North and South Korean children.

"The height gap is approximately 4cm (1.6in) among pre-school boys and 3cm (1.2in) among pre-school girls, and again the South Koreans would be taller."

Schwekendiek points out that the height difference cannot be attributed to genetics, because the two populations are the same.

"We're dealing with the Korean people," he says, "and Korea is interesting because it basically hasn't experienced any immigration for many centuries."

Martin Bloem is head of nutrition at the World Food Programme, which has been providing food aid to North Korea since 1995. He says poor diet in the early years of life leads to stunted growth.

"Food and what happens in the first two years of life is actually critical for people's height later," he says.