Data from EpiReumaPt project, which is a national, cross-sectional, and population-based study, were used (12). This study population comprised adults (≥18 years old) living in the community, in the Portugal mainland and islands (Azores and Madeira). Exclusion criteria were resident of an institution, and inability to speak Portuguese or to complete the assessment protocol. Participants were selected through a process of multistage random sampling. The sample was stratified by region and population size.

EpiReumaPt involved a three-stage approach. The first stage included the selection of potential participant household/families using a random selection process. In each household, the adult with the most recent birthday was recruited and completed a structured interview (sociodemographic, socioeconomic, anxiety and depression symptoms, lifestyle habits, chronic non-communicable diseases, health resources utilization data), and a screening for rheumatic diseases. In the second stage, all participants who screened positive for at least one rheumatic disease plus 20% of participants with no rheumatic symptoms were invited to be assessed by a rheumatologist. In the last phase, a team of three experienced rheumatologists revised all the clinical, laboratory, and imaging data and confirmed the diagnoses using validated criteria (12). Details of the EpiReumaPt methodology have been published previously (12–14).

In this study, the sample consisted of adults 50+ years old who participated in the second phase of EpiReumaPt study and were evaluated by a rheumatologist to confirm the presence or absence of OA (knee OA and/or hip OA and/or hand OA). OA was defined by rheumatologists according to expert opinion combined with the fulfillment of the American College of Rheumatology classification criteria for knee OA, hip OA, and hand OA, as described earlier (15–17).

Sociodemographic data, physical function, anxiety and depression symptoms, lifestyle (e.g., physical activity), and chronic non-communicable diseases were collected during the first stage of the EpiReumaPt project.

Sociodemographic data included age, gender, marital status, education, and work status. Marital status was categorized in three categories: without partner (single and divorced people), married, and widower. Work status was categorized as employed full time, part-time, not currently employed (domestic employed, unemployed, and students), and retired.

Number of current chronic non-communicable diseases was assessed using a comprehensive list which included the following 14 diseases: high blood pressure, high cholesterol, heart disease, diabetes mellitus, chronic lung disease, problems in the digestive tract, renal colic, neurological disease, allergies, mental or psychiatric illness, cancer, thyroid and parathyroid problems, hypogonadism, hyperuricemia, and other rheumatic diseases (OA was excluded from this list).

The Health Assessment Questionnaire Disability Index [HAQ-DI; (18)] was used to assess level of functional ability. HAQ-DI measures difficulties with the performance of 20 daily activities retrospectively over the preceding week with four possible responses: no difficulty (0 points), some difficulty (1 point), much difficulty (2 points), and unable to do (3 points). The 20 activities are classified into 8 categories with 2 or 3 activities each: dressing and grooming, arising eating, walking, personal hygiene, reaching, gripping, and usual activities (i.e., shopping, doing chores, getting in and out of a car) (18, 19). The score for each category is the single response within the category with the highest score (greater difficulty). The total score is computed as the mean of the eight category scores. As in previous studies, we did not correct HAQ-DI scores for use of assistive devices (19, 20).

To assess physical activity, participants were asked about the amount of time (minutes) per week they dedicated to physical activity. Answers were categorized as <150 or ≥150 min, based on the physical activity recommendations of the WHO (21) for older adults.

Depression and anxiety were assessed by Hospital Anxiety and Depression Scale [HADS; (22, 23)]. The HADS is a short instrument with two subscales that both have seven items that assess presence of clinical anxiety and depression. The scale has a maximum score of 21 for both anxiety and depression subscales. People with scores between 0 and 7 are considered normal, scores between 8 and 10 are borderline, and a score ≥11 indicates a mood disorder. In data analysis, anxiety and depression were considered as dichotomous variables (i.e., a participant with a score ≥11 on either subscale was considered depressed or anxious).

EpiReumaPt was approved by the National Committee for Data Protection and by NOVA Medical School Ethics Committee. All participants provided informed consent, and the study was performed according to the principles established by the Declaration of Helsinki.

Participants (N = 1,645) were divided in two groups: group 1 (n = 1,059) consisted of participants meeting the OA diagnostic criteria; and group 2 (n = 586) consisted of participants without OA diagnosis or others rheumatic diseases. There were no missing data except for physical activity (n = 485).

Descriptive analysis was used to describe the main characteristics of the sample, using frequencies (absolute and relative) or means and SDs, depending on the type of the variable. The comparison of groups defined by the presence/absence of OA (group 1: with OA and group 2: without OA) was performed using independent samples t-test for continuous variables and Chi-square test for categorical variables. Univariate logistic regression models, with presence of OA as the outcome, were performed to identify a set of factors that could predict OA presence, including sociodemographic characteristics, comorbidities, functional status, physical activity, depression, and anxiety. The final multivariable model with backward elimination included variables with p-values <0.05. Odds ratios (ORs) and 95% confidence intervals were used to assess the results. All statistical analyses were performed using Statistical Package for the Social Sciences (SPSS, version 24, IBM), and α = 0.05 was used to determine significance level.

The sample comprised 1,645 participants. The mean age of the sample was 65.3 years (SD = 9.3) and 63.2% (n = 1,040) were women. Most of the participants were married (n = 1097, 66.7%) and had 4 years of education (n = 847, 54.5%). Regarding work status, the majority were retired (n = 1050, 63.8%). With respect to number of self-reported chronic non-communicable diseases, most participants reported 0–2 (n = 720, 43.8%) and 3–4 (n = 540, 32.8%) chronic diseases. Hypertension (n = 857, 52.1%) and high cholesterol (n = 805, 48.9%) were the most frequently reported diseases. Among rheumatic diseases, osteoporosis was the most frequently self-reported disease (n = 190, 11.6%). With respect to functional status, the mean score of HAQ-DI for the total sample was 0.55 (SD = 0.65) out of 3, indicating low levels of limitations. The majority of the sample met the ≥150 min of physical exercises per week (n = 306; 63.1%). Depressive symptoms were found in 10.6% (n = 174) and anxiety was found in 13.8% (n = 227) of the total sample.

Sample consisted of 1,059 adults with OA diagnosis (64.4%) and 586 without OA diagnosis (35.6%). Among people with OA, 12.5% (n = 132) were classified as having hip OA, 44.7% (n = 473) hand OA, and 68.6% knee OA (n = 726). Among persons with an OA diagnosis, 36.6% (n = 388) reported the presence of other rheumatic diseases. In this sample, the additional rheumatic diseases most commonly reported were osteoporosis (n = 190, 11.6%) and rheumatoid arthritis (n = 91, 5.5%).

Statistically significant differences were found between groups (with and without OA) in all sociodemographic variables (i.e., age, gender, marital status, education, and work status), non-communicable diseases, functional status, physical activity, depression, and anxiety (Table 1). Participants with OA were older (mean = 67.1, SD = 9.1) than participants without OA (mean = 62.1, SD = 8.9). The proportion of women with OA (n = 774, 73.1%) was higher than among persons without OA (n = 266; 45.4%). More participants with OA were married (n = 666, 63.5%), in comparison to persons without OA (n = 425, 72.5%). Widowers were the second most common category represented, 263 (24.8%) in participants with OA compared to 71 (12.1%) in those without OA. Regarding work status, the majority of participants in both groups were retired (persons with OA: n = 749, 70.7%; persons without OA: n = 301, 51.4%). Among participants with OA, the second most frequent category was “without labor activity” (n = 158, 14.9%), whereas for persons without OA, the second most common category was “full time employed” (n = 176, 30.0%). Most persons with OA reported presence 3–4 non-communicable diseases (n = 367, 34.7%), compared to 0–2 non-communicable diseases (n = 365, 62.3%) among persons without OA. Individuals with OA were significantly less active (56.8% met the recommendation of ≥150 min of physical activity per week) than those without OA (70.8% met the recommendation of ≥150 min of physical activity per week). With respect to functional status, participants with OA showed significantly higher levels of functional limitations (mean = 0.70, SD = 0.67) than persons without OA (mean = 0.28, SD = 0.58). Percentage of depressive symptoms was also higher among individuals with OA (n = 143, 13.5%) compared to participants without OA (n = 93; 8.7%). Similar results were found for anxiety, persons with OA showed a higher percentage of anxiety symptoms (n = 172, 13.8%) than people without OA (n = 55, 9.4%).

Using OA as the outcome, unadjusted logistic regression models found that all of the variables shown in Table 1 were associated with presence of this chronic disease (Table 2). The final adjusted model contains only significant variables, and the non-significant variables were excluded, one by one, from the model. The variables were removed in the following sequence: marital status (p = 0.387), work status (p = 0.216), depression (p = 0.512), and anxiety (p = 0.066). In the final adjusted model, age, gender, number of comorbidities, physical disability, and physical activity remained statistically significant and the model explained 32% of the variance. People who were older (OR = 1.048, p < 0.001) and female (OR = 3.192, p < 0.001) were more likely to have OA. People with more than five comorbidities were more likely to report OA than people with 0–2 comorbidities (OR = 4.484, p < 0.001). Functional disability was also associated with OA. Specifically, persons with higher levels functional disability were more likely to report OA than those with lower levels of disability (OR = 1.926, p < 0.001). Physical activity was also associated with OA persons; people with lower levels of physical activity were more likely to report OA than those with higher levels of physical activity (OR = 1.630, p = 0.027).