The NORNS study was composed of an initial survey and a follow-up survey 3.5 years apart. Participants were recruited voluntarily among those aged 30 or more living in Seoul. The survey consists of a health questionnaire and medical examination. The health questionnaire comprises the following six domains: 1) demographic and migration information 2) disease history, 3) mental health, 4) health-related lifestyle, 5) female reproductive health, and 6) sociocultural adaptation. The medical examination comprises anthropometric measurements, blood pressure and atherosclerosis, and various biochemical measurements. Prevalence of several diseases able to be diagnosed from the medical examination, the changes between the two surveys, and the association between the outcome and other measurements, such as length of stay and extent of adaptation in South Korea will be investigated. Furthermore, the outcome will be compared to a South Korean counterpart cohort to evaluate the relative health status of NKRs.

Participant eligibility was limited to NKRs aged 30 or more years living in Seoul. The greatest proportion of total NKRs in South Korea, 31.2%, resides in Seoul [2]. We placed notices on the Internet and by telephone once a month with the help of the Hana Center, a representative welfare center supported by the government for assisting NKRs who have settled in South Korea, that a health questionnaire survey and medical examinations would be conducted every month for NKRs above 30 years old living in Seoul; and applicants applied to participate voluntarily. In this way, a total of 550 subjects have been recruited from October 2008 until December 2011

General socio-demographic indicators, such as occupation, level of income and education, marriage status in both North and South Korea, and age and sex were obtained. For assessing migration indices of the subjects, the time of escape from North Korea and arrival in South Korea were obtained so that the length of stay in South Korea and in third countries can be calculated. Information on the subjects' residential areas in North Korea and countries of transit and temporary asylum after defection were also included.

Past disease history and current status of 32 typical diseases in the cardiovascular system, musculoskeletal system, gastroenterological system, respiratory system, communicable diseases, and cancers diagnosed by doctors in South and North Korea were obtained.

For the systematic assessment of the NKRs' mental health, which was found to be very poor by previous studies, the following instruments were used. For identifying depression, the Korean edition of the Center for Epidemiological Studies Depression Scale, a 20-item instrument which frequently serves as a depression screening tool in epidemiological research, was used [17,18]. For identifying psychosocial stress, an 18-item psychosocial well-being index-short form composed of a 4-point scale, which has been developed and validated in South Korea, was used [19]. Information on suicide ideation and suicide attempts during the preceding 1 year was also obtained.

Health-related lifestyles, such as smoking, alcohol consumption, and exercise, were measured. Detailed smoking histories, including age at first cigarette, packs per day, and number of smoking and smoke-free years, were obtained. Alcohol consumption habits like intake amount and frequency during the preceding 12 months were assessed. We also determined whether or not subjects participated in regular exercise, in addition to the duration of such exercise.

We tried to examine the reproductive state and history of female subjects, since female NKRs accounted for three-quarters of total NKRs in South Korea, and their gynecological and obstetric health has been reported as very poor. The questionnaire has items on histories of menstrual state, pregnancy, and birth that are identical to those of KNHANES.

Searl and Ward [20] developed a scale to evaluate psychological and sociocultural forms of adjustment during the process of cross-cultural transitions. The scale was transformed into a new 29-item scale adjusted to situations NKRs have faced, and items such as 'making friends,' 'using the transport system,' and 'talking about yourself with others' are included in the new adaptation scale.

The basic medical examination, which was conducted for all subjects, consists of anthropometric measurement, blood pressure and atherosclerosis examination, biochemical measurement, thyroid sonogram, and bone densitometry (Table ​(Table11).

Height, weight, and body mass index were recorded. Body fat mass and body fat percentage (BFP) were measured by bioelectrical impedance analysis (Inbody 720; Biospace, Seoul, Korea). The BFP measurement that is derived from a bioelectrical impedance analysis is less accurate than measurements obtained by dual-energy X-ray absorptiometry. However, this method of estimating body composition has become increasingly popular because it is easy to use, non-invasive, relatively inexpensive, provides an accurate method for the assessment of body composition, and can be performed across a wide range of subjects with regard to age and body shape [21]. Waist circumference, measured in triplicate at the midpoint between the lower rib and the iliac crest, and hip circumference, measured in triplicate at the point yielding the maximum circumference over the buttocks, were also included.

Systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured by an automatic blood pressure monitor (TM-2655P; Biospace, Japan) on the arm of a seated subject who had rested in a sitting position for 10 minutes before the measurement. The TM-2655 device achieved British Hypertension Society grade A/A and therefore can be recommended for blood pressure measurement in an adult population [22]. The mean of the two SBP and DBP measurements at least 5 minutes apart were used for the analysis. After a subject had rested in a supine position for 5 minutes, brachial-ankle pulse wave velocity (baPWV) and ankle-brachial index were measured using a volume-plethymographic apparatus (model VP 1000; Colin, Komaki, Japan). This instrument simultaneously records baPWV and the brachial and ankle blood pressures on the left and right sides. baPWV is considered a risk marker [23] and prognostic predictor of atherosclerosis [24]. baPWV is a newly developed device using a volume-rendering method. Due to its technical simplicity and short sampling time, baPWV is more appropriate for screening a large population than previous methods. The validity and reliability of the automated device for measuring baPWV have been established previously [25].

Blood samples were drawn after an overnight fast. Serum total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, uric acid, and liver enzyme levels were determined by enzymatic methods with a chemistry analyzer (TBA 200-FR; Toshiba, Japan). Plasma glucose was measured by the glucose oxidase method. High-sensitivity C-reactive protein was determined by latex turbidimetry (TBA 200-FR; Toshiba). Serum insulin was measured with an insulin radioimmunoassay kit (Diasource, Nivelles, Belgium), which had a reactivity of less than 0.2% to human proinsulin. Insulin resistance was estimated using the homeostasis model of assessment, calculated as fasting glucose (mmol/L) × fasting insulin (mU/L)/22.5. Microproteinuria was measured with turbidimetry (TBA 40-FR; Toshiba). Various adiopocytokine levels and thyroid functions were also measured.

We employed a defected North Korean doctor who has the same background and experience as general NKRs. We had him have one-to-one interviews with all subjects and verify the important items of the questionnaire with his cultural and linguistic knowledge, whereby we tried to enhance the validity and completeness of the subjects' reports.

The phase 2 follow-up survey started April 2012, which is 3.5 years after the first subject group was examined with the phase 1 survey. Subject recruitment for the phase 2 survey also will be aided by the Hana Center which has the contact information of the subjects, and only for voluntarily applied ones. Survey process and measurements are almost identical to the phase 1 survey methods, but additional examination will be provided.