AMONG the many things for which North Korea is remarkable, it must have the densest concentration of slogans in the world.

“Destroy the aggressors with merciless annihilating blows,” counsels one, emblazoned above a Pyongyang highway. “Each Korean must perform selfless feats to glorify the heroic deeds of leader Kim Jong Il,” advises a second.

In recent years visitors — and defectors to Seoul, the South Korean capital — have described the strangest of all. It is seen in schools, gymnasiums and other places where children gather.

Compared with the usual tone of socialist ferocity, it is direct and almost pleading: “Try to grow taller.”

It is the closest thing to an official acknowledgement of one of the hidden catastrophes of North Korea: after a decade of food shortages, and four years of outright famine, a generation of its children has stunted growth.

Those few foreigners allowed to visit or live in the country report the same experience: encountering a group of children several years older than they appear. Teenagers look like pre-pubescent children. Young soldiers doing their military service look like 14-year-olds.

Professor Pak Sun Young, a South Korean anthropologist, has conducted studies on North Korean defectors in Seoul, and on refugee children living clandestinely in the bordering regions of China. They had escaped the worst privations of a homeland where between a few hundred thousand and a few million people died of hunger in the late 1990s. She found that 70 per cent of the survivors of that catastrophe were stunted, and 25 per cent underweight.

The average 14-year-old boy was 10in (25.4 cm) shorter than his average South Korean peer and 42lb (19kg) lighter. The average 17-year-old was 5ft tall, compared with 5ft 8in in the South.

Even with improved access to food and medical care, many will never catch up.

The situation has consequences for North Korea’s national defence, its economy and for any future reunification with South Korea. Young North Korean defectors in South Korea are taunted and discriminated against already because of their short stature.

“It’s not that being short is bad in itself. The problem is the idea of body image in South Korean society,” Professor Pak said. “Tall people are respected, and North Koreans feel very uncomfortable about being shorter.”

Kim Jong Il, North Korea’s hereditary leader, is reputed to wear platform boots to boost his 5ft 3in.

Getting accurate information from the most closed country in the world is almost impossible, but the few available statistics indicate the scale of the problem. Despite great improvements in food distribution since the famine of 1995-99, malnutrition has left 42 per cent of North Koreans stunted, according to the United Nations World Food Programme.

North Korean children are being encouraged to play basketball, which is believed to promote growth. In this, they can point to a great success: in a bitter irony, Lee Myong Hun, the world’s tallest player at 7ft 9in, is North Korean.

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