Data collection and population
As part of data collection for the surveillance of chronic disease and nutrition among Chinese adults which was conducted across eight monitoring sites in Inner Mongolia, multi-stage stratified cluster sampling was used to ensure a representative cross-section of the population. This research included adult over 55-year-old including 820 residents.
Ethnics approval and consent to participate
This survey was approved by the Ethical Committee of the National Institute for Nutrition and Food Safety, Chinese Center for Disease Control and Prevention. In this survey, there were no treatments, interventions that could impact the health of participators. All participants provided written informed consent before the start of the investigation.
Questionnaire and Measures
The survey was administered by trained health facility staff members, and included items related to demographic characteristics, such as age, gender, ethnicity; health-related behaviors, such as smoking, and diseases status, including diabetes, dyslipidemia, and so on.
Information about consumption of condiments such as cooking oil, salt and aginomoto was collected using a weighing method. Condiments purchased and wasted were also recorded. In the 24-hour recalls, participants recalled and described all food and alcohol consumption for 3 consecutive days. The food consumption and frequency with past 12 months were collected by the standard food frequency questionnaire.
Participants’ height and weight were directly measured by trained and evaluated workers. Blood and urine samples were also collected. The laboratory director organized the quality control sample assessment at a field laboratory.
Variable Definitions
Sodium intake
The dietary sodium intake contained all food which collected by a weighing method and 24-hour recalls. According to the China Food Ingredients Table (version Ⅱ) [16], sodium intake in each type of food was calculated. Then the sodium intake was categorized into two levels according to the intake recommended by the Chinese Nutrition Society, sodium intake ≤ 2200 mg was defined as moderate, and sodium intake > 2200 mg was defined as excessive[16].
Alcohol Consumption
Drinking frequency, type (liquor with high content alcohol, liquor with low content alcohol, beer, yellow rice wine, rice wine, wine) and average drinking amount were measured. The average alcohol consumption per day was calculated according to the Manual of Chinese Chronic Disease and Nutrition Surveillance Survey. One standard drinking unit equals 10 g of alcohol. Participants’ average daily drinking amount was divided into three levels according to the Dietary Guidelines for Chinese Residents 2016: never (0 g/d), moderate (Male ≤25 g/d, Female ≤15g/d), and excessive (Male >25 g/d, Female >15 g/d) [17].
Definition of Hypertension
The main outcome indicator was hypertension. Meeting one of the following conditions was considered to indicate hypertension. The first condition was self-reported hypertension; that is, having a diagnosis of hypertension and currently receiving hypertension treatment[13]. The second condition was field-measured hypertension, assessed as the average of three blood pressure measurements carried out by trained investigators and defined as average systolic blood pressure ≥ 140 mmHg and/or average diastolic blood pressure ≥ 90 mmHg.
Definition of other variables
Ethnicity were categorized as Han, Mongolian or other minorities. Marital status was categorized as single, married, or others. Education level was categorized as primary school, junior high school or high school and above. Smoking status was categorized as nonsmoking (never having smoked previously), former smoking (previously smoked but has quit) or current smoking(has smoked at least 1 cigarette/d for more than 1 year and smokes now). Physical activity was assessed by the questionnaire, and defined as low, medium and high. Body mass index ( BMI ) was categorized as BMI < 24 kg/m2, BMI = 24 – 28 kg/m2) or BMI ≥ 28·0 kg/m2.
Statistical Analyses
In univariate analysis, we compared residents with hypertension and without hypertension by social-characteristics, which used chi-squared tests. Furthermore, we categorized the participants into 6 subgroups according to the sodium intake status and drinking levels, and analyzed the prevalence of hypertension and sodium intake with drinking. We then used logistic regression to assess the risk of both demographic predictors, behavior, and disease status of hypertension ( No hypertension=0, Hypertension=1). The interaction between sodium intake and drinking on hypertension was also analyzed; the multivariate models were adjusted by educational level, BMI, family history of hypertension, physical activity, diabetes and dyslipidemia. Finally, we compared the single effect of sodium intake and drinking on hypertension. Forward LR was used to select variables in logistic regression. Statistical significance was determined by a<0.05. All statistical analyses were performed with SPSS software version 19.0 ( IBM Corp, Armonk, NY, USA ).