Study population
A total of 39,259 subjects aged 18-79 years were recruited from Henan Rural Cohort Study, which was a prospective study focused on chronic non-communicable diseases. Detailed description of this cohort study design, methods, and participants recruitment have been previously published [19], and the cohort was registered in Chinese Clinical Trial Register (Registration number: ChiCTR-OOC-15006699). In short, the study was conducted in Yuzhou, Xinxiang, Tongxu, Yima and Suiping county of Henan Province, with the baseline survey has been completed from July 2015 to October 2017. For the current analysis, after excluding participants who were missing data on SUA level (n=54), had malignant tumor and serious renal disease (n=350), and those with incomplete information about sleep data (n=9212), 29,643 adults (12,128 men and 17,515 women) were included in final. The protocol of this study was approved by the Zhengzhou University Life Science Ethics Committee. Informed consent was obtained from all participants.
Assessment of potential covariates
The potential covariates including demographic covariates, lifestyle factors and the family history of disease were collected by well-trained staffs using a standardized questionnaire. Demographic covariates included age, gender (male or female), education level (“primary school or below” or “middle school or above”), marital status (“married/cohabitating” or “unmarried/divorced/widowed”) and per capita monthly income (“<500 RMB”, “500-1000 RMB” or “≥1000 RMB”). Lifestyle factors included smoking status, drinking status, physical activity and dietary pattern. Smoking status was classified into never, current, and former groups. Drinking status also was classified into never, current, and former groups. Physical activity was divided into three levels (low, moderate and high) based on the International Physical Activity Questionnaire (IPAQ) [20]. Dietary pattern was categorized four types as previously by using a standard principal component analysis method [21], dietary pattern I with a high intake of red meat, white meat and fish; pattern II with a high intake of vegetables, staple food, and fruits; pattern III with a high intake of grains, nuts, beans, pickles and animal oils; and pattern Ⅳ with milk and eggs. In addition, obesity (yes/no), hypertension (yes/no), T2DM (yes/no) and dyslipidemia status (yes/no) were assessed as previous definitions [16], family history of gout (yes/no) also was obtained.
Assessment of sleep variables
Sleep quality and related sleep variables were assessed using the Pittsburgh Sleep Quality Index (PSQI), which is a validated self-report questionnaire consisting of 19 elements to assess sleep quality and disturbances [22]. The Chinese version PSQI used by us has been widely used to assess sleep quality with good overall reliability (r=0.82-0.83) and test-retest reliability (r=0.77-0.85) [23]. For the snoring frequency, participants were asked two questions (1) Do you know, or have you ever heard that you snore? (yes or no) and (2) How often do you snore during the past month? (never, rarely snore<1 day per week, occasionally for 1–2 days per week, habitually≥3 days per week) [24]. Daytime napping was assessed by asking participants “Did you take a nap usually over the past year?” Those who answered yes were further asked to report the average daytime napping duration. Napping duration was reclassified into 0 min (reference), 1-30 min, 31-60 min, 61-90 min and ≥91 min [18]; in addition, self-reported night sleep duration also was determined based on answers to the questions: “On average how many hours actual sleep duration did you get at night during the past month?” Night Sleep duration was grouped as <5, 5-6, 6-7, 7-8 (reference), 8-9, 9-10, and ≥10 hours [25].
Definition of HUA
Blood samples were collected from individual antecubital vein after at least 8h of overnight fasting to measure multiple biochemical indicators. SUA level was measured by ROCHE Cobas C501 automatic biochemical analyzer with enzymatic colorimetric method. Definition of HUA was determined as SUA level >417μmol/L (7.0 mg/dL) and >357μmol/L (6.0 mg/dL) for men and women, respectively [15].
Statistical analysis
All analyses were conducted using IBM SPSS V.19.0 and R 3.5.0. Descriptive statistics included one-way analyses of variance and chi-squared tests were conducted to compare the differences of baseline characteristics according to the HUA status of participants, including demographic and socio-economic characteristics, lifestyle risk factors, and sleeping variables. Multivariable logistic regression models were performed to explore the associations between sleep variables (snoring frequency, daytime napping and night sleep duration) and prevalence of HUA. Interactions were tested by adding interaction terms of these sleep variables by pairwise combination, respectively. Moreover, multivariable linear regression analyses were conducted to evaluate the relationship of these sleep variables with SUA level. Three models were constructed: model 1, age-, sex-adjusted model; model 2, adjusted for age, gender, education level, marital status, average monthly income, smoking status, drinking status, physical activity and dietary pattern; model 3, model 2 plus adjustment for snoring, daytime napping and night sleep duration where applicable.
Based on the results of logistic regression analyses, the subgroup analyses were further conducted to examine whether the significant associations between snoring or daytime napping (each 30min increment) and prevalence of HUA were modified by age, gender, obesity, hypertension, T2DM and dyslipidemia status. To test the robustness of the results, sensitivity analyses also were performed to repeat the regression analyses by gender or additionally adjusting for family history of gout, obesity, T2DM, hypertension and dyslipidemia conditions. A P-value < 0.05 was considered to be statistically significant.
Furthermore, snoring frequency, daytime napping and night sleep duration also were recoded as never, rarely (<1 day/week), occasionally (1–2 days/week), and habitually (≥3 days/week) and 0 min, 1-30 min, 31-60 min, and ≥61 min and <7, 7-8, 8-9 and ≥9 hours for combined effects, where the combined never snoring and no napping group, never snoring and night sleep duration (7-8 hours), and no napping and night sleep duration (7-8 hours), served as the reference categories, respectively.