1 Study Design
The data were derived from the Psychology and Behavior Investigation of Chinese Residents (PBICR) project. PBICR spanned from June 20, 2022, to August 31, 2022, encompassing 31 provinces (including autonomous regions and municipalities directly under the central government) of China. This study employed a robust multistage sampling method across 148 cities, 202 districts and counties, 390 townships/towns/streets, and 780 communities/villages. Using China's population pyramid as a reference, quota sampling was meticulously performed on selected residents in ten cities. This process encompassed attributes such as gender, age, and urban/rural distribution to ensure that the resulting samples mirrored the demographic characteristics of the overall population.
The survey was carried out through the Wenjuanxing network platform, the most popular survey software in China (https://www.wjx.cn/). Participants accessed a dedicated link to complete the questionnaire. In cases where respondents possessed cognitive abilities but lacked the ability to complete the questionnaire, the researcher conducted individual interviews and subsequently addressed the questions on their behalf. This study was approved by the Institutional Review Committee of Ji’nan University, Guangzhou, China (JNUKY-2021-018). All the participants fully understood the study and voluntarily signed informed consent forms.
2 Participants
The inclusion criteria were as follows: ① age ≥ 12 years; ②nationality of the People's Republic of China; ③ permanent resident in China (with an annual absence from home ≤ 1 month); ④ voluntary enrollment in the study and successful completion of the informed consent form; ⑤completion of the online questionnaire either on their own or with the help of the investigator; and ⑥understanding the meaning of each entry in the questionnaire.
The exclusion criteria were as follows: ① experiencing delirium or mental abnormalities; ② experiencing cognitive dysfunction; and ③ currently involved in other similar research projects. ; ④ Individuals expressing unwillingness to cooperate.
A total sample size of 21,916 individuals was included, and the research scope of this study included residents aged 18–60 years. Invalid data, such as age nonconformity, logical errors, and abnormal levels of physical activity, were excluded, resulting in the completion of the survey by 14,358 people (Fig. 1).
3 Assessment of Dietary Behaviors and Physical Activity Intensity
3.1 Dietary Behaviors
Poor dietary behaviors were defined as follows[21]: ①Preference for sugar beverages: characterized by an average consumption exceeding four bottles (1,200 ml) per week in the past year; ②Drink: indicated by a habitual intake of alcoholic beverages (including beer, yellow wine, white wine, red wine, etc.); ③Skipping breakfast: defined as eating breakfast no more than twice in the past 7 days; ④Preference for takeaway: characterized by consuming takeaway meals/eating out (excluding cafeteria) more than three times in the past 7 days; and ⑤On diet: indicated by engaging in intermittent fasting/lightfasting behaviors during the past year.
3.2 Physical activity intensity
The PBICR follow-up interview questionnaire collected data on the quantity and duration of highly physically demanding activities (such as lifting heavy objects, plowing, aerobic exercise, etc.), moderately vigorous physical activities (such as lifting light objects, tai chi, sprinting, etc.), and light physical activities (such as walking) carried out by the respondents during the previous week. First, using the metabolic equivalent (MET) assignment of each physical activity in the short version of the IPAQ (International Physical Activity Questionnaire), we estimated the respondents’ energy expenditure regarding physical activity over one week. The METs for light-intensity, moderate-intensity, and high-intensity physical activity were 3.3, 4.0, and 8.0, respectively. The intensity level of physical activity is determined by multiplying the MET value assigned to the particular activity type by the frequency per week (d/w) and amount of time per day (min/d). The sum of these three intensity levels represents the total physical activity level. Physical activity was classified into three categories based on the IPAQ rubric: low-intensity physical activity (< 600 METs/min per week), moderate-intensity physical activity (600–3000 METs/min per week), and high-intensity physical activity (> 3000 METs/min per week). To enable comparative analyses with international studies on physical activity levels, two categories of physical activity levels were established: low intensity and moderate-to-high intensity[22].
4 Anxiety and Depression
As a widely used self-report anxiety questionnaire, the 7-item Generalized Anxiety Disorder Scale (GAD-7) has demonstrated robust reliability and validity in general population studies[23]. In the context of this research, the GAD-7 served as a concise screeing tool to identify anxiety levels, employing seven items rated on a 4-point Likert scale ranging from “not at all” to “nearly every day”. The total score, ranging from 0 to 21, reflects the severity of anxiety symptoms, with higher scores indicating greater severity. Specifically, scores of 0–4 denote no symptoms, 5–9 indicate mild symptoms, 10–14 indicate moderate symptoms, and 15–21 signify severe symptoms. In this study, we considered a score greater than 5 to be the criterion for determining the presence of anxiety symptoms. In addition, the Cronbach’s α was 0.954 in this study[24].
The Patient Health Questionnaire-9 (PHQ-9), designed to screen for depression in accordance with the criteria of the Diagnostic and Statistical Manual of Mental Disorders, has been identified as a highly reliable screening tool[25, 26]. Each of the nine questionnaire items is rated based on frequency, ranging from 'not at all' to 'nearly every day.' The total score ranges from 0 to 27, with higher scores indicating more severe depression. Specifically, scores between 0 and 4 indicate no symptoms, 5–9 indicate mild symptoms, 10–14 denote moderate symptoms, and 15–27 signify severe symptoms. We also set 5 as the cutoff score in this study. The Cronbach’s α of the PHQ-9 was 0.939.
5 Covariates
This study included demographic covariates, including a range of sociodemographic factors: age, sex, urban‒rural status, educational status (illiterate, primary, junior high, high school, university and above), occupation (student, employed, unemployed/retired), region (east, central, west), marital status (unmarried/divorced/widowed, married), living alone or not, mode of healthcare (no healthcare, with healthcare), and per capita monthly income (less than 3,000, between 3,000 and 6,000, 6,000 and over).
6 Statistical analysis
The quantity and percentage of categorical variables, as well as the mean and standard deviation of continuous variables, were calculated using descriptive statistics. We applied the chi-square test to compare anxiety and depression symptoms among dietary behaviors and physical activity intensity. Ordered logistic regression was used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for depressive and anxiety symptoms, dietary behaviors and physical activity intensity. Covariates were adjusted in Model I and Model II: age, sex, marital status, urban or rural status, education, career status, residential status, insurance status, and per capita monthly household income. Model I included the variables number of poor dietary behaviors and physical activity intensity, and Model II included the variables type of poor dietary behaviors and physical activity intensity. Furthermore, a restricted cubic spline was performed to explore the dose–response relationship between anxiety and depression rates and the number of dementia behaviors. All tests in this study were two-sided with a significance level of P < 0.05. Participants were categorized by sex and age for subgroup analysis. SAS 9.4 (Inc.) and R 4.2.2 (drc package) statistical software were used to perform all the statistical analyses.