Data collection was based on the Portuguese National Asthma Survey - Inquérito Nacional sobre Asma (INAsma), a nationwide population-based cross-sectional telephone interview survey that included two phases.
Sample size calculation, based on an asthma prevalence of 6% in the general population
] and considering attrition rates of 20-40% and unstable variables (e.g. non-response), revealed that 665–776 asthmatics needed to be identified and 7,387-12,927 households to be interviewed.
The first phase of the INAsma aimed to estimate the prevalence of asthma symptoms in the Portuguese population. The study design was described in detail elsewhere
]. Briefly, to obtain a representative sample of the general population, a stratified cluster sampling was used. We selected a random sample of households within each municipality (stratum), using a list of landline phone numbers. Within each selected household, the last household resident to have his/her birthday was selected. If this individual was younger than 15 years we interviewed the caregiver. Individuals unable to understand spoken Portuguese or with cognitive or physical conditions hampering the interview were excluded. The phone interview was based on the GA2
]. The simple response rate was 40%; the corrected response rate 50%.
The second phase mainly aimed at estimating the proportion of asthma patients with controlled disease in Portugal. Asthmatic and healthy respondents from the first phase were contacted again, as well as asthmatic household members from first phase respondents. PA was measured with the short telephone version of the International Physical Activity Questionnaire (IPAQ), using last week recall. Asthma control was assessed by CARAT, the control of allergic rhinitis and asthma test
Current asthma was defined as self-reported asthma and at least one of these criteria: one or more symptoms (wheezing, waking up with breathlessness or having an asthma attack) in the last twelve months, currently taking asthma medication or an asthma medical appointment in the previous twelve months.
was defined as a CARAT global score > 24 or a CARAT second factor score ≥ 16
Healthy subjects were defined as individuals without atopy, heart disease or any respiratory symptom related to asthma, bronchitis, rhinitis or sinusitis.
Walking, moderate and vigorous PA,
as well as total PA
, were expressed as MET-min/week (metabolic equivalent)
]. For each PA level and daily sitting time
, respondents were classified according to their gender-specific median value (≤ median and > median)
], as well as according to the ACSM/AHA 2007 PA guidelines
]. Overall PA
level was classified in the health-enhancing, moderate or low level PA category
● Health-enhancing PA level (HEPA) was defined as a) vigorous activity on ≥ 3 days achieving ≥ 1500 MET-min/week, or b) ≥ 5 days of walking, moderate and/or vigorous activities achieving ≥ 3000 MET-min/week.
● Moderate PA level was defined as a) ≥ 3 days with ≥ 20 minutes of vigorous activity, b) ≥ 5 days with ≥ 30 minutes of moderate activity and/or walking or c) ≥ 5 days of walking, moderate and/or vigorous activities achieving ≥ 600 MET-min/week.
● Low PA level was defined as any activity level not meeting the criteria for moderate or health-enhancing PA.
● Body mass index (BMI) was calculated from self-reported weight and height (kg/m2). Socioeconomic status (SES) was categorized as high (A social class), medium (B and C social classes) and low (D social class), based on the occupation and education of the person who financially contributed most for the household. Smokers were defined as respondents having smoked at least one cigarette per day or one cigar per week during one year. Current smokers smoked in the last month, ex-smokers reported having quit smoking at least one month preceding the survey.
Data entry was done automatically by Computer Assisted Telephone Interviews (CATI). Only individuals who met the age criterion (18–69 years) and with valid IPAQ and CARAT answers were considered for analysis (Figure
). Truncation rules were applied. Data were analyzed separately for men and women. Categorical variables are presented as frequencies and percentages, continuous variables as median and interquartile range (IQR). χ2 tests and Mann–Whitney/Kruskall-Wallis tests were used to compare groups. Crude and adjusted logistic regression analyses were performed to assess associations between asthma and PA. P-values < 0.05 were considered statistically significant. Adjustments were made for variables significantly associated with both asthma status and any PA level: age and BMI for men and age for women (data not shown). For the multinomial logistic regression, a main effects model was used. Results are presented as odds ratios (ORs) with the respective 95% confidence intervals (95%CI). Data were analyzed by using SPSS Statistics 17.0.
Participants flowchart. From the 17 698 households contacts, 6 003 participants were included in the 1st phase and 1584 in the 2nd phase of INAsma survey. A total of 606 healthy and 133 asthmatics were considered for physical activity analysis.
The study was approved by a Hospital Ethics Committee (Comissão de Ética do Hospital de São João, Porto). All participants gave oral informed consent and were informed that they could abandon the study whenever they pleased. Data confidentiality was guaranteed by storing personal information separately from the study data.