The Nutrition and Health in Southwest China (NHSC) study: design, implementation, and major findings

Study design and overview

The NSHC is a prospective cohort study initiated in winter 2013. Using a sampling design stratified by urban and rural locations, a representative sample of Chinese adults was drawn from the general population in Southwest China (0.49 million sq.km, 144.1 million residents [6], Fig. 1). In total, 54 study sites (23 communities and 31 villages) were included as of December 2018. At each site, a two-stage (household-person) sampling method was used. Of the households listed within each site by the resident offices, 150 were randomly selected. Eligible participants were adults aged 18–70 years to facilitate follow-up, only persons who had lived in their current residence for at least 1 year were eligible to participate. When a member of the household refused participation or was unavailable, a replacement household was selected using a simple random sampling method from all households of similar composition in the same site, excluding the already selected households. The replacement households were recruited to ensure an adequate sample size within each selected site; they also helped to maximize the representativeness of the surveyed communities with regard to the prevalence of major chronic diseases as well as the distributions of age, gender, educational, and individual economic status. The study was approved by the Ethics Committee of Sichuan University. All participants provided written informed consent for the examinations.

Fig. 1: Location of the Nutrition and Health in Southwest China (NHSC) study.
figure1

Including Sichuan, Guizhou and Yunnan provinces.

The baseline data collection was completed in December 2018 and follow-ups are conducted every 2 years. Figure 2 displays an overview of the study protocol and examination timeline. Up to now, at least one follow-up assessment has been completed for participants recruited in 2013, 2014, 2015, and 2016, with two follow-ups completed for participants recruited in 2013 and 2014.

Fig. 2: Examination timeline of the Nutrition and Health in Southwest China study.
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The baseline data collection was from 2013 to 2018 and follow-ups are conducted every 2 years.

Data assessment

All assessments of participants in the NHSC Study have included (and continue to include) questionnaires, anthropometric measurements, medical examinations and biochemical measurements. Table 1 shows a list of exposure and outcome variables available from the NHSC study instruments.

Table 1 Design and major components of the Nutrition and Health in Southwest China study.

Nutrition assessment

Dietary intake data are collected via three 24-h recalls and a food frequency questionnaire (FFQ). The 24-h recalls were obtained by trained investigators in face-to-face interviews first on the day of registration and subsequently on two other days (selected by the participants) within a 10-day period from the registration day. For 24-h recalls, details on recipes as well as the types and brands of all food items reported were obtained. Dietary intake data from the 24-h recalls were converted into nutrient intake data using the continuously updated in-house nutrient database, which was based on the China Food Composition [7].

Participants’ consumption of foods and food groups over the last year was collected via a 66-item interviewer-administered FFQ [8]. The frequency values of FFQ range from never consumed to consumed more than five times per day using the standard serving size for food groups. Nutrient intakes were then calculated by multiplying the frequency of consumption of each food or beverage by the nutrient content of the portion and summing the intake of each nutrient for all items.

Eating behaviors

Eating behaviors relevant to diet quality of the participants were obtained by questionnaire. Participants were interviewed about the number of times per week they ate breakfast, time and place they ate breakfast, and foods commonly eaten for breakfast. Similar details (time, location, commonly eaten foods) were obtained for lunch and dinner. In addition, participants were interviewed concerning the frequency of having dinner with family, the frequency of snacking and food type of snacks, and the frequency of eating outside the home. Moreover, the local diet specialties were considered.

Physical activity

Level of physical activity was assessed by a physical activity questionnaire with 38 items validated for Chinese adults [9]. Participants were asked the usual type, frequency and duration of activities over the past 12 months. Participants are also asked “What kind of transportation do you usually use when you go to work?”. The frequency and duration of sedentary behaviors were also obtained, including watching television, using computers, using smart phone, reading, and playing cards or mahjong.

Lifestyle-related information

Participants were asked to report their smoking habits. For the ex-smokers and current smokers, number of cigarettes smoked per day and duration of cigarette smoking in years were also collected.

The sleep duration and sleep quality of the participants were assessed using the Pittsburgh sleep quality index scale, in which 19 individual items generate 7 component scores [10]. In addition, the frequency and duration of napping were obtained.

The assessments of work and life stress were based on the participants’ subjective rating of work and life stress. Participants are asked “how often do you feel stressed at work/in daily life?” and the level of stress they felt. The response options for the participant’s level of stress included not at all stressful, not very stressful, a bit stressful, quite a bit stressful, and extremely stressful.

Depression and mental disorders

Since 2015, the depression status of the participants has been assessed by trained investigators, using the 17-item Hamilton Rating Scale for Depression (HDRS-17) [11]. The Chinese version of HDRS-17 has been shown to have acceptable validity and reliability [12]. In addition, information on mental health status has been collected since 2017, using the Mini-Mental State Examination [13].

Anthropometric measurements

All anthropometric measurements were performed by trained investigators with the participants dressed lightly and barefoot. Height and weight were measured to the nearest 0.1 cm and 0.1 kg, respectively, using an Ultrasonic Weight and Height Instrument (DHM-30, Dingheng Ltd, Zhengzhou, China). Waist circumference was measured at a point midway between the lowest rib margin and the iliac crest in a horizontal plane using a nonelastic tape. Hip circumference was measured to the nearest 0.1 cm at the maximal gluteal protrusion. Skinfold thicknesses were measured on the right side of the body to the nearest 0.1 mm using a Holtain caliper (Holtain Ltd., Crosswell, United Kingdom). All anthropometric measurements were performed twice for each participant.

Blood pressure

After a 5–10 min rest in a quiet environment, blood pressure was measured twice using a mercury sphygmomanometer on the right upper arm of participants. Systolic and diastolic blood pressures were recorded for each participant.

Biochemical measurements

Blood samples were drawn after an overnight fast of at least 10 h for all participants at every visit. Venous blood specimens were collected using vacuum blood collection tubes containing anticoagulant sodium fluoride or ethylenediaminetetraacetic acid. Blood samples were centrifuged and stored at 4 °C for subsequent analysis. The biochemical assessments are shown in Table 1.

Genomics

Genomic DNA was extracted from peripheral blood lymphocytes using standard methods. The stock samples were split into five tubes and stored at different locations at −80 °C. DNA samples were genotyped using the Infinium II technology from Illumina (Human HAP300 panel).

Additional information

The sociodemographic characteristics were obtained via a questionnaire: including age, place of residence, marital status, family size, personal income per month, family income per year, years of education, and employment status. Family history of chronic diseases as well as the timing of menarche and menopause was also collected.

Quality assurance procedures

Prior to study implementation, a 3-day training was conducted at the study offices of each site. An operation manual was developed detailing all standardized procedures. To improve the accuracy of the estimated portion sizes during dietary assessment, standard serving bowls, plates and glasses, and a photo book containing photos of snacks and beverages were displayed to the participants. Finally, to encourage participants to complete the examination, each of them was given the results of their clinical examination at no charge within a week after the visit.

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