Prevalence, treatment, control of type 2 diabetes and the risk factors among elderly people in Shenzhen: results from the urban Chinese population

We recruited people 65 years old and above from the lists of all residents registered at local community health service centers from January 2018 through December 2018 in Shenzhen by convenience sampling. One hundred forty-one thousand six hundred eighty-four people were recruited into the study, which accounted for 36.9% (141,684/383,700) of the resident population of elderly adults in Shenzhen based on data from the 2015 population census. A questionnaire, blood sample test, and physical examinations were provided during the study. We collected data from local community health service centers. After excluding individuals with incomplete data, 124,007 subjects (87.5%) completed the entire study. All participants signed the written informed consent before entering the study. If the participants were not able to write or read, we contacted their relatives to inform them and signed on their behalf. The study protocol was approved by the ethics committee of Shenzhen Center for Chronic Disease Control (SZCCC-201802).

After blood collection, all participants were interviewed face to face. A standardized questionnaire was administered by trained staff to obtain information on sociodemographic information (e.g., date of birth, gender, educational level, etc.), previous history (e.g., history of previous disease, operation history, history of trauma, etc.), family history (e.g., hypertension, diabetes, coronary heart disease, chronic obstructive pulmonary disease, malignant tumor, stroke, etc.), lifestyle (exercise frequency, smoking status, drinking habit, etc.), and medication use under the supervision of trained general practitioners and nurses (Additional File 1). Weight, height, waist circumference (WC), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were measured with the use of standard methods.

We defined the educational level as illiterate, primary education, junior school education and above. And marital status was classified as married or cohabiting, widowed, divorced and single. The definition of the answer “yes” in physical exercise was participants who take exercise that causes sweating and shortness of breath for more than once a week [17]. Participants’ drinking habit (habitual drinker, non-habitual drinker and non-drinker) and smoking status (current smoker, ex-smoker and never-smoker) were categorized as described elsewhere [18, 19].

The research staff members had completed the training course about the entire study and received a written project operation manual, which included detailed instructions on the questionnaire surveys, physical examination index measurement, and blood sampling.

After overnight fasting, anthropometric examinations were performed in the morning. Physical examination measurements were taken according to standard procedures [20]. Height and weight were measured with the participants wearing light clothing without shoes. WC was measured horizontally at the midpoint of the midaxillary line between the twelfth rib head and the superior anterior spine, at the end of a normal exhalation. Body mass index (BMI) was defined as the weight (kg) divided by squared height (m²). By using standard-certified sphygmomanometers, the participants’ right arm blood pressure at the heart level was measured three times. We take the average of the results in three measurements as the final blood pressure value. Participants were prohibited from drinking coffee, smoking, or exercising, within 30 min before the physical examination.

With more than 8 h of overnight fasting, participants’ vein blood samples were taken. The clinical laboratory at each grade 2 hospital (community health service center is directly affiliated to the hospital) analyzed the samples. All participating laboratories had completed a standardization and competency program. Fasting venous blood was drawn from subjects to measure the fasting plasma glucose (FPG) level by automatic biochemistry analyzer. Glucose oxidase measurements were used to determine the FPG level.

Participants were regarded as T2D if one of the following three conditions was met: (1) previously diagnosed by professional doctors, (2) FPG ≥ 7.0 mmol/L, (3) 2-h plasma glucose level ≥ 11.1 mmol/L. [21] Treatment was defined as the rate of people with diabetes who had taken diabetic medication. Control was defined as the percentage of diabetic patients with FPG < 7.0 mmol/L.

Hypertension was defined as SBP ≧140 mmHg and/or DBP≧ 90 mmHg and/or self-reported treatment with antihypertensive medication within 2 weeks [22]. We defined overweight as a BMI between 24.0 to 27.9, and obesity as a BMI ≥ 28.0. The definition of central obesity was WC equal or more than 85 cm in females and 90 cm in males according to the Healthy Adult Weight Determination in China (WS/T 428–2013) [23].

Characteristics of the study subjects were described as mean ± standard deviation for continuous variables and number (percentage) for classified variables. In our analysis, continuous variables in different groups were analyzed by t-test or variance analysis, and classified variables were analyzed by the chi-square test. To detect risk factors of older diabetic patients, multivariate logistic regression models were estimated. Model fittings were conducted using backward elimination with a threshold of 0.10 for variable inclusion in the model. Odds ratios were calculated with 95% CIs. Statistically significant was regarded as a level of two-sided P < 0.05. SAS version 9.4 software (SAS Institute, Cary, NC, USA) was used in the data cleaning and analyzing process.

The sociodemographic characteristics of elderly population in Shenzhen were shown in Table 1. One hundred twenty-four thousand seven participants were investigated in the study. The study population had an average age of 71.3 years old. There were 54,649 male subjects (44.1%) and 69,358 female subjects (55.9%). The socio-demographic characteristics of the study population were statistically different in the two gender subgroups. The BMI, SBP, WC, FBG were higher in females than that in the male group. While males were older, had higher DBP, and a lower rate of CVD history. Also, the education level, marital status, physical activity status, smoking habit, and drinking habit were all statistically different between both genders.

As shown in Table 2, 22.5% of elderly urban Chinese residents had diabetes. Among people with diabetes, 54.8% received medical treatment. Only 34.4% of those who were treated had their glycemic controlled. The prevalence and treatment rate for T2D increased with age and then decreased in participants more than 80 years old (25.5, 56.9%). While older people aged 80 years old or more had a higher control rate (37.5%). The prevalence and treatment rate had no difference in males and females. However, men have a significantly higher rate of control than women (35.2% vs 33.7%). Also, higher treatment rate was found in the group with higher education levels (57.5% vs 50.3%). Single older participants had lower prevalence and treatment rates when compared with participants who had companions. Higher prevalence, treatment, and control rates were found in people with regular physical activity. Ex-smokers had the highest prevalence, treatment and control rates in contrast to current smokers and non-smokers. Habitual drinkers had the highest treatment rate and the lowest diabetic prevalence. Participants with the previous history of CVD, obesity, central obesity, or hypertension had higher prevalence and control rates than those without.

By applying univariate and multivariate logistic regression analysis, risk factors on the prevalence, treatment, and control of diabetes were found. For the results see Table 3. Older age (aOR = 1.2, 95%CI: 1.2–1.3), drinking (aOR = 1.2, 95%CI: 1.1–1.2), history of CVD (aOR = 1.5, 95%CI: 1.4–1.6), high BMI (aOR = 1.2, 95%CI: 1.2–1.3), central obesity (aOR = 1.2, 95%CI: 1.2–1.3), and history of hypertension (aOR = 1.9, 95%CI: 1.8–1.9) were risk factors of the prevalence of diabetes while physical activity (aOR = 0.9, 95%CI: 0.9–1.0) was negatively related to the prevalence rate. For elders with T2D, a higher education level (aOR = 1.3, 95%CI: 1.2–1.5), physical activity (aOR = 1.2, 95%CI: 1.1–1.2), ex-smoker (aOR = 1.2, 95%CI: 1.1–1.3), central obesity (aOR = 1.2, 95%CI: 1.1–1.2), and hypertension (aOR = 1.2, 95%CI: 1.1–1.3) were positively related to the treatment rate of diabetes. In contrast, habitual drinker (aOR = 0.7, 95%CI: 0.6–0.8) and high BMI (aOR = 0.7, 95%CI: 0.7–0.8) were negatively related to the treatment rate. Physical activity (aOR = 1.1, 95%CI: 1.0–1.2), low BMI (aOR = 1.4, 95%CI: 1.1–1.6), history of CVD (aOR = 1.4, 95%CI: 1.3-1.6) and hypertension (aOR = 1.5, 95%CI: 1.5–1.6) were positively related to the glycemic control of diabetes, while primary education (aOR = 0.8, 95%CI: 0.8–0.9), current smoker (aOR = 0.9, 95%CI: 0.8–1.0), and central obesity (aOR = 0.9, 95%CI: 0.8–0.9) were negatively related to that.