The main aim of this study is to measure HL in the adult population residing in the municipality of Leiria over the next 10 years. As secondary objectives, it is intended to characterize anxiety and depression, metabolic risk, alcoholism, and smoking in the in the same population sample and over the same period. The research design follows a longitudinal, prospective closed cohort study of Leiria's residents during ten years. Strengthening the report of observational studies in epidemiology (STROBE) guidelines were applied in alignment of the research objectives. The frequency of data assessment is set to two years, so participants will be contacted five times during the study. The sample will consist of residents of the municipality of Leiria aged 18 years or over, having been determined a sample size of 4003 (2001 men and 2002 women).

The team that conducted the 1st wave survey will be composed by 32 interviewers, who will be recruited by the Center for Innovative Care and Health Technology (ciTechCare) coordination board through a selection process composed of 2 stages: interview selection plus a theoretical and practical training session. The follow-ups of the cohort were decided to be conducted every two years by call. In the 1st wave a face-to-face interview will be conducted with the Computer Assisted Personal Interview (CAPI) system: all interviewers have a tablet with the software (LimeSurvey) which provided the questionnaire, designed by ciTechCare research team, applied to all subjects. Surveys will be administered online via the LimeSurvey platform at baseline and at 2 years, 4 years, 6 years, and 8 years post baseline (5 waves). The baseline and follow-up surveys will comprise the same battery of validated questionnaires and instruments designed to collect information on sociodemographic, lifestyle aspects (tobacco and physical activity), anthropometric variables, auto-report chronic diseases, metabolic risk, anxiety and depression and HL. It will take approximately 30 minutes to complete the survey.

Metabolic risk is assessed by the Finnish Diabetes Risk Score (FINDRISC), to evaluate symptoms of anxiety and depression we applied the Hospital Anxiety and Depression Scale (HADS) Portuguese validated version and HL will be measured by European Health Literacy Survey Questionnaire (HLS-EU-Q47).

Descriptive statistics (mean, standard deviation, median, minimum, maximum, interquartile range, absolute and relative frequencies) will be computed to describe the cohorts' sociodemographic characteristics. At baseline comparisons between groups (eg with and without anxiety) will be undertaken using t-tests for continuous normally distributed variables or Wilcoxon for continuous non-normally distributed variables. Chi-squared tests will be used for categorical variables, and Fisher's Exact test will be used for categorical variables within smaller sample sizes. Comparison between more than two groups will be performed through one-way analysis of variance (ANOVA) for continuous variables and chi-squared test for categorical variables. Factors significantly associated with any disease group will be included in a logistic regression model for further analysis. The effect of specific conditions on HL will be assessed by linear regression, univariable and then multivariable, controlling for potential confounders and also analyzing potential effect modification. Taking into consideration follow-up, the changes in HL, anxiety and depression will be each evaluated by means of variance analysis with measurement repetition. After checking the statistical model pre-requisites, sociodemographic characteristics will be added by means of linear regression analysis in the final model.