A population-based diabetes survey was conducted in 2009 in three rural regions (Jimo, Huangdao, Jiaonan) in Qingdao, China. A stratified, random cluster sampling method was used to recruit a representative sample of the general rural population aged 35–74 years living in selected villages for at least 5 years. A total of 5556 individuals living in selected villages were invited and 3757 individuals participated in the survey, giving a response rate of 67.6%. From June 2012 to May 2013, a total of 3108 participants who did not have diabetes at baseline screening were invited for re-examination. Of these, 1782 individuals attended the second examination (follow-up rate 57.3%), with 1656 participants provided complete information for the current data analysis.
After an overnight fast, all the participants without previously diagnosed diabetes underwent a standard 75 g oral glucose tolerance test (OGTT) from 07:00 to 11:30 h at the local survey sites, and blood samples were collected from the antecubital vein into a vacuum tube containing sodium fluoride. Plasma glucose was determined by the glucose oxidase method. All participants received their glucose test results one or two months after the survey.
The surveys were approved by Qingdao Municipal Health Bureau and ethics committee of the Qingdao Municipal Center For Disease Control and Prevention. Written consent was obtained from all participants before the surveys.
In both examinations, all the participants were interviewed at the local survey sites by a trained survey team consisting of doctors and nurses. Family history of diabetes was defined as at least one first degree relative (parents, siblings or offspring) having diabetes. Education was classified as illiterate, elementary school (1–6 years), junior high school (7–9 years) and high school or above (≥9 years formal education). Personal monthly income was classified as income < ¥300/month, ¥300-¥999/month, ≥¥1000/month (1 euro ≈ 7.2 chinese yuan¥). Height and weight were measured with participants wearing only light clothes and without shoes. For surveys carried out in winter, 1 or 2 kilogram was subtracted from the measured weight of individuals depending on the woolens they wore. Body mass index (BMI) was calculated as weight in kilograms divided by height in meter squared (kg/m2). Waist circumference was measured at the mid-point between the rib cage and the iliac crest to the nearest 0.1 cm. All information was recorded on standard paper-based questionnaires during the interview both at baseline and follow-up. All the participants received health tips from the survey doctors or nurses during the interview and at the time when they were contacted again with their screening test results. No additional education sessions have been provided to the participants by the survey team.
We used an interview-based 15D instrument to measure the overall HRQoL at baseline and follow-up . The 15D questionnaire consists of 15 dimensions: mobility, vision, hearing, breathing, sleeping, eating, speech, excretion, usual activities, mental function, discomfort and symptoms, depression, distress, vitality and sexual activity. Each dimension is divided into five ordinal levels, by which more or less the attribute is distinguished. The single index score (15D score), representing the overall HRQoL on a 0–1 scale (1 = full health, 0 = being dead) are calculated from the health state descriptive system using a set of population-based preference or utility weights. The minimal clinically important change or difference in the 15D score is ±0.015 .
The 15D questionnaire usually takes 5–10 minutes to complete. A Chinese version of the 15D questionnaire was translated according to the established international guidelines and in consultation with the original 15D developer (Harri Sintonen) and validated in Chinese individuals with a range of glucose tolerance status before it was administrated to the survey participants and also used in other published study .
The changes in HRQoL in the pre-diabetes and normoglycaemia group was assessed for the entire group, as well as for a subgroup who did not develop diabetes at 3 years in order to exclude the potential influence of the diabetes status.
Depressive symptom measurement
The Zung self-rating depression scale (ZSDS) questionnaire was used to survey depressive symptoms . The scale consists of 20 items using a four-point-grading system, ranging from “none or a little of the time” to “most of or all the time”. The completed questionnaire score ranges from 20 to 80. Individuals were classified into four groups based on their ZSDS scores: 20–44 normal range, 45–59 mildly depressed, 60–69 moderately depressed, and ≥70 severely depressed.
To evaluate the individual physical activity (PA), daily walk steps were counted using a questionnaire recommend in Physical Activity Guideline for Chinese Adults  by Ministry of Health in China. The questionnaire investigated five major types of daily physical activity patterns of Chinese adults: walking, housework, leisure time PA, cycling, and occupational PA. Four types of daily physical activity patterns except for occupational PA were considered in the current study. Each type of PA includes specific activities such as walking, cooking, taking care of children or group dancing etc. that are most common among Chinese adults. Participants reported the minutes per day of PA and frequency per week of each specific activity during the past week. Each specific activity based on the total amount and intensity was then translated into walk steps. The calculation was based on the Compendium of Physical Activities , which is a coding scheme that classifies specific PA by rate of energy expenditure. The energy expenditure of 1000 walk steps was equal to walking at 4 km/hour (METs = 3) for 10 minutes (1000 steps = 1/2 MET-hr). During the data analysis, physical activity level was arbitrarily classified as low (<6000 steps per day), moderate (6000–9999 steps per day), and high (≥10 000 steps per day).
The consumption of fresh vegetable was evaluated by an interviewer-administered 54-item food quantitative frequency questionnaire  that incorporated 54 kinds of food, beverage and other items that are commonly consumed in China. Participants reported the intake frequency and amount of fresh vegetables during the past year on a daily, weekly, monthly or yearly basis. Participants were classified into three categories based on fresh vegetable consumption of <7 times, 7–13 times, and ≥14 times per week.
Differences in the ZSDS score, BMI, weight, waist circumference, frequency in physical activity and fresh vegetable consumption between baseline and follow-up were calculated for pre-diabetes and normoglycaemia categories classified according to the baseline screening glucose tolerance test results. The baseline HRQoL, ZSDS and lifestyle measures were recorded before the participants received their glucose test results.
Classifications of pre-diabetes and normoglycaemia
Individuals who were free of diabetes at baseline were further classified into pre-diabetes and normoglycaemia according to the World Health Organization/International Diabetes Federation 2006 criteria . Pre-diabetes was defined if a baseline fasting plasma glucose (FPG) fell between 6.1 and 6.9 mmol/l and/or 2 h plasma glucose (2hPG) between 7.8 and 11.0 mmol/l; normoglycaemia was defined if a FPG < 6.1 mmol/l and 2hPG < 7.8 mmol/l. Diabetes was defined as FPG ≥ 7.0 mmol/l and/or 2hPG ≥11.1 mmol/l. Individuals with diabetes at baseline including those with a prior history of diabetes were not included in the current data analysis.
Changes over time in the continuous variables (HRQoL, ZSDS, BMI, weight) within each group were analysed using the paired Student’s t test and in categorical variables (Physical activity, vegetable intake) using the McNemar’s test (binary) or Marginal homogeneity test (multinomial), respectively.
Differences of changes between the two groups were determined with analysis of co-variance (ANCOVA), adjusting for the corresponding baseline values of HRQoL, ZSDS, BMI and weight. The statistical analysis was performed using PASW statistics (Version 18.0.2, Chicago: SPSS Inc; April 2, 2010). Two-sided p-values <0.05 were considered statistically significant.