After the armistice agreement of the Korean War, North and South Korea were divided into two different governments and have different socio-economic environments. Especially from the 1980s, a significant gap in the economy gradually developed, and North Korea has suffered from absolute poverty and famine because of natural disaster and the economic failure of communism [1]. From 1998, a robust exodus began and has increased ever since. North Korean refugees (NKRs) enter into China, and many of them wish to settle in South Korea permanently. Indeed, the number of NKRs that have entered into South Korea has gradually increased from 1,400 in 2000 to 23,000 in 2012 [2], and their settlement has brought about important issues in South Korean society from many different aspects including the medical field.

Currently, many studies have been conducted focusing on the mental health of NKRs. In association with the stressful conditions during the defection and resettlement, NKRs are susceptible to depression, post-traumatic stress disorder or other psychological disorders [3,4,5,6,7,8]. In addition, NKRs generally have small and thin physiques because of nutritional deficiency during adolescence and are vulnerable to infectious diseases such as helminthic [9] or tuberculosis infections [10]. However, there are still issues not resolved such as the general health of NKRs and how their health changes after settling in South Korea. The aim of this study was to investigate these issues.

In the present study, height, weight, and body surface area were significantly smaller in all NKRs than that of the South Korean controls, except for females aged over 50 years. In females, young NKR participants with more than a 4-year stay in South Korea had higher weight and fat mass than those with a shorter duration in South Korea (less than 4 years). All NKRs had a weaker grip strength than that of the South Korean controls. Taken together, the NKRs had relatively lean body compositions and weak muscle strength than that of the South Korean controls.

Consistent with other studies [14,15,16], the NKRs showed small physiques than that of the South Korean controls. The mean body height, weight, body surface area, and waist hip ratio were smaller in NKRs than that of South Korean controls in both male and female. The discriminative factors of body composition were different between their genders: NKR men had smaller muscle mass while women had smaller fat mass than that of the South Korean controls.

More interestingly, young female NKRs showed differences body compositions according to their durations of South Korean stay. Body weight and fat mass were significantly higher in NKR ≥4 group than that of the NKR <4 group, which were comparable to that of the South Korean women. Additionally, young female NKRs showed positive correlations between body weight and their duration of stay in South Korea, while NKR over 50 years of age showed no correlation. One of the possible explanations is that young NKRs have been suffering from extreme starvation in their childhood because of the natural disaster and economic collapse of North Korea since the 1970s. These might resulted in the bigger differences of body compositions between young and elders female NKRs, especially who has a shorter duration of the South Korea stay. Interestingly, the difference in body composition was much less in young female NKRs who stayed in South Korea more than 4 years. The present study is hard to clarify the impacts of the duration of South Korean stay on body composition, because of the limitations of a cross-sectional design. Further study is need to verify whether younger NKRs were more susceptible to environmental changes or not.

Although our data have the limitations of a small-sized, cross-sectional observation study, we were able to gain some insights. Because NKRs, especially those underwent absolute malnutrition in their early lives, have frail physiques, an increase in body fat and muscle mass after re-settlement in South Korea might be beneficial to their general health. Still, there are also some concerns about it. According to the thrifty phenotype hypothesis, the experience of nutritional insufficiency drives the whole body metabolism to energy storage phenotypes [17]. In later life with sufficient nutrition, these subjects have increased susceptibility to altered metabolism, such as diabetes, hypertension, stroke, or coronary heart disease [18]. Similarly, sudden exposure to excess foods could cause serious metabolic alterations especially in younger NKRs who underwent extreme severe malnutrition in their childhood or infancy. Thus, especially for younger NKRs, a well-designed nutritional program might be needed to improve their health conditions.

Another interesting finding in this study was that the weak muscle strength of NKRs was quantified with the grip strength measurement. NKRs had a weaker grip strength for both genders, and the mean grip strength of women was close to meeting the criteria of sarcopenia [19]. Different from other body compositions, there was no difference in grip strength between the different groups for the duration of stays in South Korea. Sarcopenia and sarcopenic obesity, which have increased in South Korean elderly, are currently well-established risk factors for cardiometabolic diseases including diabetes and coronary heart disease [20,21,22]. Related to the findings that younger female NKRs with longer South Korean stay and elder female NKRs had a similar body weight and fat mass to that of South Koreans, weaker muscle strength could cause serious alterations in whole body metabolisms including glucose intolerance or metabolic syndrome. There is on-going cohort study, named North Korean refugee health in South Korea [23]. A total of 440 NKRs were initially recruited and medical examination, including anthropometric measurements and biochemical analyses, will be followed after 3.5 years from initial recruitment. Up-coming data form this cohort would provide valuable information to unsolved questions in the present study.

In this study, body composition analyses has been performed using bioelectrical impedance analysis method, which calculates total body water, body fat, body weight, and fat-free body mass by measuring electrical impedance through whole body tissues [24]. Although it is simple and easy to access in clinics, the results is not as accurate as dual X-ray absorptiometry, since it estimated body composition indirectly [25]. Further validation study using more accurate method such as dual X-ray absorptiometry or computed tomography is needed.

In conclusion, body composition analyses showed that NKRs have a relatively poor health status. Environmental changes after resettlement in South Korea might have bidirectional impacts on the health conditions of NKRs, both beneficial and harmful. A specific health support program is need based on their age and gender.