International food aid has been provided since the United Nations Food Shortage Report on NK was published in mid-19990s, and several surveys have assessed maternal and child health to verify the effectiveness of the food aid (Table 1) [4-10]. The birth rates of low birth weight infants were 6.4% in 2000 and 6.7% in 2002 but gradually decreased to 3.1% in 2017. Among children under 6 months of age, the exclusively breastfed rate increased from 69.6% in 2002 to 88.6% in 2009 and then gradually decreased to 71.4% in 2017. The vitamin A supplementation coverage rate in children aged 6–59 months was 80.2% in 2000 and gradually increased to 97.8% in 2012. The percentage of children receiving oral rehydration solutions during an episode of diarrhea was 90.9% in 2000 versus 74.1% in 2017.

The proportion of more than 4 antenatal care visits was 95% in 2004 versus 93.7% in 2017. The proportion of skilled birth attendants was 96.7% in 2000 versus 99.5% in 2017. The proportion of childbirths that occurred at the health facility was 94.7% in 2009 versus 92.2% in 2017.

Among children under the age of 5 years, the underweight rate was 60.6% in 1998 and then gradually decreased to 18.8% in 2009 and 9.3% in 2017. Similarly, the rates of wasting and stunting decreased from 15.6% and 62.3% in 1998 to 2.5% and 19.1% in 2017, respectively.

Fig. 1 shows the immunization rates of NK children from 1998 to 2019 [11]. The Bacillus Calmette-Guérin vaccine immunization coverage rate was 69% in 1998 versus 96% in 2002. It decreased to 88% in 2003 and then continued to fluctuate gradually, reaching 96% in 2019. The DTP3 (third dose of diphtheria and tetanus toxoids and pertussis-containing vaccine) immunization coverage rate was as low as 43% in 1998 but has continued to increase since then, reaching 97% in 2019. The Pol3 (third dose of polio vaccine) immunization coverage rate was 82% in 1998, increased to 99% in 2002, and was 98% in 2019.

The MCV1 (first dose of measles-containing vaccine) immunization coverage rate was 49% in 1998 and increased rapidly to 98% in 2002, and then gradually fluctuated, reaching 98% in 2019. The coverage rate of the HepB3 (three-dose hepatitis B vaccine) was very low at 27% in 2003, increased sharply to 98% in 2004, and remained at 97% in 2019.

The changes in the leading cause of death in children with NK between 2000 and 2019 using data from the Institute for Health Metrics and Evaluation [12] are shown in Fig. 2. Among children under 5 years of age, protein-energy malnutrition was the most common cause of death in 2000 but sharply decreased in 2019, while the rates of measles and whooping cough decreased similarly in 2019. However, the rates of lower respiratory infections and diarrheal diseases were higher in 2019. In addition, the rates of injuries, such as drowning, foreign bodies, and road injuries, increased in 2019 compared to 2000.

In children aged 5–14 years, the most common cause of death in 2000 was protein-energy malnutrition, which decreased sharply in 2019, similar to what was noted in children under 5 years of age. The same infectious diseases, measles and meningitis, also declined in 2019, whereas lower respiratory infections maintained a similar ranking in 2019. The rates of injuries (drowning, road injury, interpersonal violence, and falls) and noncommunicable diseases (leukemia, congenital defects, brain cancer, and other malignant neoplasms) increased in 2019.

The backgrounds of NKR children can be divided into several categories [13]: those who were born in NK but have moved to SK; those who were born in a third country such as China after one of their parents left NK and subsequently entered SK; and those who were born in SK after a parent settled in SK. The Ministry of Unification data includes only children born in NK. In fact, it is estimated that there are more NKR children living in South Korea than reported. These children are highly likely to have poor nutritional status at birth and have a low socioeconomic status (SES), even after settling in SK [14]; therefore, their nutritional status must be regularly monitored.

After the NK famine of the mid-1990s, researchers have aimed to determine the growth and nutritional status of NK children using UN survey data (Table 2). In a study comparing the height and weight, NK children were 6–7 cm shorter and about 3 kg lighter than SK children [15]. In another study, NK children were up to 13 cm shorter and up to 7 kg lighter than SK children (Table 3) [16].

As the food shortage persisted and many NK citizens began escaping the country, investigators became concerned about the growth and nutritional status of NKR children (Table 4). NKRs generally stay in third countries (mainly China) for months to years before entering SK. One study assessed the growth status of NKR children residing in China [17]. The heights and weights of 436 NKRs aged 4–19 years old were measured, and their growth statuses were only 70%–90% of those of SK children.

Immediately after entering SK, NKRs undergo a medical examination at Hanawon. Some studies have evaluated the growth status of NKR children using Hanawon health data (Table 4). Of them, 30.2% were shorter than the 3rd percentile of the SK standard, while 27.9% weighed less than the 3rd percentile of the SK standard [18]. Similarly, another study using the Hanawon data of NKRs aged 6–20 years who entered SK in 1999–2007 reported that they were up to 16.3 cm shorter and up to 15.3 kg lighter than SK children [19]. Several other studies evaluated nutritional status using Hanawon health data. Among 283 NKRs younger than 18 years, the prevalence of stunting was 29.4%, that of underweight was 10.4%, and that of wasting was 0% [20]. Another similar study reported that, among 109 NKRs aged 7–14 years, 18.6% were stunted and 14.7% were underweight [21].

Once NKRs settled in SK, researchers investigated whether the nutritional status of the children had improved (Table 5). In one study, the researchers investigated 70 NKR children who had settled in SK [22]. They reported that the children’s nutritional status improved from 11.4% to 5.7% for stunting and 14.3% to 1.4% for underweight by approximately 2 years after settling in SK. However, compared with sex- and age-matched SK individuals, NKR children were still significantly shorter and leaner than SK subjects [23]. In a study of 301 NKR children, the authors reported that the prevalence of stunting, underweight, and wasting was 7.6%, 5.6%, and 5.0%, respectively [24]. Another study of 526 NKRs under 18 years who had lived in SK for approximately 4 years showed improved nutritional status, with the prevalence of stunting, underweight, and wasting of 7.0%, 6.8%, and 5.3%, respectively [25]. The authors demonstrated that, despite this improvement, the nutritional status of NKR children remained serious, given that the subjects included children born in SK as well as children born in NK or third countries. In addition, comparison of the nutritional status of children born in the mid- to late 1990s and children born after 2000 revealed that the prevalence of stunting, underweight, and wasting among individuals born in the mid- to the late 1990s was higher than those born in NK after 2000. In the mid- to late 1990s, the food situation in North Korea was at its worst, and people born during this period are now entering adulthood, so their health status in adulthood should be carefully monitored. It is important to verify the thrifty phenotype hypothesis, which is the associations between poor nutrition in early life and the subsequent development of type 2 diabetes and the metabolic syndrome, by monitoring the incidence of chronic diseases in this population.

Shortly after NKRs enter SK, malnutrition remains a major health problem [21]. However, the prevalence of obesity increases in this population over time (Table 6). NKR children now face the “double burden” of both under- and overnutrition [25]. In a study using Hanawon data for NKRs, none of the children had a weight higher than the 97th percentile [21]. Moreover, using Hanawon data, another study reported that the prevalence of obesity was 1.4% at the time of SK entry but increased to 5.7% after approximately 2 years [22]. Approximately 4.2 years after NK children settled in SK, the prevalence of obesity had increased to 9.1% [25].

The association between SES and the health and nutritional status of children is well known [26]. Researchers recently evaluated whether this relationship is consistent with NKRs. In a study of 139 NKRs and 1,029 SK children aged 8–13, when SK children were classified into 4 SES groups (highest, moderate-high, moderate-low, and lowest) according to monthly household income, the prevalence of stunting and underweight of NKR children was significantly higher than that of SK children with the lowest SES [27]. Similarly, in a study of 112 NKR and 224 sex- and age-matched SK preschool children, the prevalence of stunting and obesity in NKR children was significantly higher than that of SK children with a low SES [28].