This cross-sectional observational study will be designed to explore the influence of movement behaviours on the association between air pollution and health outcomes of primary school-children. A collaboration with the Northern Regional Educational Board and with Physical Education (PE) teachers from the selected primary schools will be established to collect the primary data in the school context. We will use the logistic and material resources from the CIAFEL (Centro de Investigação em Actividade Física, Saúde e Lazer) and the EPIUnit (Unidade de Investigação em Epidemiologia) research centres to optimize financial and human resources for the project.
The project will follow scientific procedures to describe observational studies (STrengthening the Reporting of OBservational studies in Epidemiology- STROBE) [28].
Ethical issues and data protection:
This project will follow all the ethical aspects related to research with human beings and vulnerable populations, and was approved by the Ethics Committee of the Faculty of Sport University of Porto (CEFADE 32-2023). The study follows the EU General Data Protection Regulation under close supervision of the Data Protection Office of the Institute of Public Health from the University of Porto (ISPUP).
Participants and their legal guardians will be invited for voluntary participation. Given the participants' age, in addition to their assent, written consent will be asked of their guardians, approving the involvement in data collection, storage, and use of the information for research purposes. Risks caused by the cardiorespiratory fitness assessment are of minor impact and similar to those in Physical Education classes and school breaks (e.g., falls, sprains). We will minimize it by close interaction with the educators, and including only small groups (one class per session) for assessment. Although the integration of GPS technology in tracking children may raise ethical concerns related to children´s privacy, we will develop a robust consent mechanism involving parents, children, and the school, to ensure transparent communication on the purposes and security of the assessed information, as well as the empowering of families and schools with the right to choose how and when to use the device. We will use devices purchased specifically for this purpose and not mobile applications, so the data collected will be maintained offline and available only to the research team. All project-specific documents (except signed consent) will be stored securely in confidential conditions, and the participant will be referred by an anonymous identification code, not the name or other trackable information. A protected cloud-based platform will be designed and open to the research team, to centralize data into a common repository. Data will be made available just to members of the MOVE-AIR project. Once data analysis is complete, data will be kept for three years after the project is complete, and then will be destroyed following data destruction standard guidelines [29]. All the participants and legal guardians will receive individual reports, and the schools will receive a general anonymous report.
Setting and participants
The project will be conducted in Porto Metropolitan Area. Three primary schools in the urban parishes of Matosinhos municipality, and three primary schools in the suburban parishes of Valongo municipality will be conveniently invited to be part of the study. Schools in urban and suburban areas will be selected to ensure enough variability in the air quality parameters to be assessed. For instance, in urban areas, there are schools in the city centre, close to the beach and in the Porto airport zone, while in the suburban area, the schools are in agricultural areas. Currently, there is no study that assessed the associations under investigation and our primary outcomes in the target population. The minimum sample size required for this project was estimated using typical values for the health outcomes to be measured, considering an alpha error of 0.05, and 15% increase/decrease due to exposure, and an effect size of 0.36. Based on these criteria, the minimum sample size of 22 children (9-to-11 years-old) was estimated to be recruited. To account for anticipated refusals and drop-outs during the assessment period, an additional 20% was added, bringing the total number of children to be recruited to 27. Typical neurodeveloped children who agree to participate and whose legal guardians give consent will be eligible for the study.
Since schools have at least one class for each of the 3rd and 4th level of schooling (approximately 20–25 children per school), 6 schools (3 in each living context) will be invited to participate in the project to recruit the number of children that we need to assess, since this number is expected to be lower in suburban areas due to the lower number of inhabitants of the selected suburban context.
We will obtain all pedagogical and institutional approvals in each school. The pre-screened schools will be contacted by a research team member to ensure they meet our inclusion/exclusion criteria (i.e. agree in participating; provide a room for biological outcomes´ assessments; provide a PE class for cardiorespiratory fitness assessment). If a pre-screened school does not attend the eligible criteria, other school in the same area will be selected.
Assessments
All participating children will undergo assessments involving various exposure variables, outcome variables, movement behaviours, and additional covariates. Regarding exposure variables, indoor and outdoor air pollutants, specifically PM2.5, PM10 and carbon dioxide (CO2), will be measured. The settings (indoor vs. outdoor) and the time children spend in each environment throughout the day will be tracked using a global positioning system (GPS). Health outcomes will include the evaluation of salivary inflammatory biomarkers, such as Interleukin 6 (IL-6) and Tumor Necrosis Factor Alpha (TNF-α), as well as oxidative stress parameters like Total Antioxidant Status (TAS) and Total Oxidant Status (TOS). From these measurements, the Oxidative Stress Index (OSI) will be calculated. Additionally, cardiopulmonary fitness will be assessed through a cardiorespiratory field test. Movement behaviours, including PA, sedentary behaviour, and sleep duration, will be monitored using accelerometers. Information regarding children's sex, age, and parental socioeconomic status will be collected through parent-provided questionnaires. Below, we describe these assessments in more detail.
Biomarkers
Children will be directed individually to a private school´s room to assess biological health outcomes. They will receive Salivette® tubes (SARS51.1534, SARSTEDT, DE) to collect a saliva sample between 8.00–10.00 a.m., at least 60 minutes after liquid or solid food intake or tooth brushing. The collected material will be stored in ice-cold conditions and immediately transported to the Biochemistry laboratory of the Faculty of Sport. After swab centrifugation, saliva will be collected, aliquoted in microtubes, and stored at -80ºC for later assessment of pro-inflammatory markers and oxidative stress parameters. Salivary Total Antioxidant Status (TAS) is usually used to measure the overall antioxidant level, and Total Oxidant Status (TOS) is usually used to estimate the overall oxidant level. These parameters will be measured by commercially available kits (EBC-K801-M and E-BC-K802-M, respectively; Elabscience, USA). The ratio of TOS to TAS will be used to calculate the Oxidative Stress Index (OSI), an indicator of the degree of oxidative stress. Salivary pro-inflammatory biomarkers IL-6 and TNF-α will be quantified by commercially available ELISA kits, according to the company instructions (#43057 and #430207, respectively, BioLegendm, USA). Children with evident periodontal disease (e.g. periodontitis) or dental plaque will be excluded of the saliva collection process to avoid bias [30].
Cardiopulmonary fitness
Children´s cardiopulmonary fitness will be assessed using the reliable, valid, and feasible cardiorespiratory fitness test 20-mSRT [31], based on the prototype of Léger [32], to predict maximal aerobic power (i.e., the maximal oxygen uptake - \(\:\dot{V}{O}_{2max}\); ml·kg-1·min-1) from maximal running speed, defined as the maximal aerobic speed. This test will be performed by running continuously between two points at a distance of 20 m. The time of change from one point to another will be determined by audio feedback via a characteristic ‘beep’ sound. Children will run to an audible signal pace at an initial speed 8.5 km·h-1 and speed will be increased by 0.25 km·h-1 every minute. After each minute, a vibrating sound will indicate an increase in speed level (level change). This test terminates when the participant: i) is unable to continue the test because of fatigue or other symptoms (voluntary withdrawal), or ii) fails to reach the marker on time for 3 times.
Movement behaviours: Physical activity, sedentary behaviour, and sleep
Participants will wear tri-axial accelerometers ActiGraph wGT3X on their left hip for 24-hours per day, over 7 consecutive days. The devices will be initialized to record at 90 Hz and the subsequent data will be downloaded using ActiLife (versions 6.13.4). The raw data files (gt3x format) will be processed in R using package GGIR version 2.8-2. The raw triaxial accelerometer signals will be converted to one omnidirectional measure of body acceleration (Euclidean Norm Minus-One; ENMO) expressed in milligravitational units (mg) [33]. For this, the vector magnitude (VM) will be taken from the three axes and then subtracted by the value of gravity (g) as in (x2 + y2 + z2) ½– 1, after which, negative values will be rounded up to zero, referred to ENMO. Data will be further reduced by calculating the average values per 1-s epoch. Then, we will calculate the average of these 1-s epoch values over the 7 monitored days to represent the average acceleration to be included in the statistical analyses. Signal processing will be done offline in R (http://cran.r-project.org/). The resulting values will be expressed in gravity-based acceleration units (g), where g = 9.81 m·s− 2. Children´s specific hip ENMO cut-points of 48 mg [34], 201 mg, and 707 mg [35] will define the estimated upper threshold of sedentary time and lower threshold of light, moderate, and vigorous physical activity, respectively. Sleep duration will be estimated using a polysomnography-validated accelerometer algorithm [36] valid for children´s use in the hip, based on the distribution of change in the z-angle (i.e., corresponding to the axis positioned perpendicular to the skin surface). All the children will receive the accelerometer diary with instructions, which will be completed by their parents. Parents will receive a daily message via mobile to remember about the use of the device and the completion of the diary.
Air pollutants and global position system
Children will use optical sensors to continuously assess PM10 and PM2.5. CO2 will be measured by nondispersive infrared sensors, following national regulations for resolution and maximum admissible errors. The settings (indoor/outdoor) where children spend their daily time will be tracked using a global position system (GPS). Ambient temperature and relative humidity will also be measured. Due to battery life constraints, air pollutants will be measured for 48 hours, comprising two representative weekdays (between Tuesday and Thursday). During this period, the sensors will be used at all times, precisely tracking air quality and position values at every minute.
The selection of sensors for air quality pollutants was based on the following criteria: the existence of validation data published in peer-reviewed journals and meeting the specifications presented in Despacho 1618/22 of February 9th [37] (Table 1).
Table 1
– Requirements for indoor air quality measurement instruments, according to Portuguese Legislation – in Despacho 1618/22 of February the 9th .
Parameter | Reference method | Equivalent methods | Max admissible error | Resolution |
---|
CO2 | Nondispersive infrared (NDIR) sensors | Electrochemical sensors Fourier transform infrared spectroscopy (FTIR) Photoacoustic sensor (PAS) | 50 ppm or 10%, whichever greater | 1 ppm |
PM10 and PM2.5 | Gravimetry | Laser or UV-based optical dispersion Beta ray absorption sensors Tapered element oscillating microbalances (TEOM) Piezoelectric resonance | 10 µg/m3 or 10%, whichever greater | 1 µg/m3 |
The MH-Z19B nondispersive infrared CO2 sensor was selected to integrate the system [38], while the NOVA SDS011 optical dispersion sensor was used to measure PM10 and PM2.5 [39]. The DHT22 sensor was used to measure ambient temperature and relative humidity [40]. The NEO6MV2 module was used to track geolocation as latitude and longitude. An HW-125 SPI reader with a 16GB microSD card was used for local data storage. A DS3231 real-time clock (RTC) equipped with a 3V emergency battery was used to track time. The inclusion of the RTC over GPS time was to avoid timestamp data losses due to eventual signal loss. The system was continuously supplied 5V DC through a commercially available external power bank (BI-B61). The system, which we named as MIDAS (Fig. 1), was controlled by an ESP32 microcontroller and the firmware was programmed in C++, using Arduino IDE. The ESP32 was chosen due to being low-cost, having integrated Bluetooth and showing high overall performance with low energy expenditure. MIDAS was programmed to take a measure of each parameter every minute, including date, time, temperature (ºC), relative humidity (%), CO2 (ppm), PM10 and PM2.5 (ug/m3), and latitude and longitude (º). In order to improve precision, particulate matter measurements were based on the average count of particles performed in the last 30 seconds, calculated by the SDS011, rather than the instantaneous count [39]. The sensors were installed into a separate case positioned in the backpack strap to capture readings close to the children's breathing area.
Data collection protocol
The research team will be in each school for one month. This period was established to guarantee two weeks of assessments for each class, due to the number of available devices to assess at least 22 children in each school. The class will perform the Fitnessgram Test, and each child will receive an accelerometer to be used for 7 consecutive days, and a backpack containing the optical air quality monitoring system and GPS, to be used for 2 consecutive days (from Tuesday to Monday), and will be instructed on the correct way to use them. In that day, all the children will be provided with parent´s questionnaire to collect sociodemographic information (please see Supplementary file 2) and an accelerometer diary, along with clear instructions for completion. At the beginning of the second week, children will return the devices, the questionnaire, and the diary, and will carry out the salivette® assessment. The entire assessment protocol will last 7 days for each class. In the subsequent week, another class will be assessed.
Data processing and statistical analysis
We will synchronize location and accelerometer data. The GPS and accelerometer data will be matched by date and time using existing software to obtain a dataset where for each recorded GPS point there is a measure of activity.
The location-based categorization of the matched data points will be conducted in a geographical information system, ArcGIS Pro 3.1 (ESRI, Redlands, CA, USA). Each participant’s data points will be imported into ArcGIS Pro. Participant’s home and school will be geocoded and also imported into ArcGIS Pro. Participant’s data points will then be overlayed with home and school locations, as well as cartography depicting administrative/census boundaries, land uses, green space/vegetation levels, proximity to roads and industry, and other geographical features. This will allow us to characterize children’s activity spaces in terms of setting (home and school, outdoor and indoor) and in terms of built, biophysical and social characteristics and to identify hotspots of high and low air pollution exposure.
For the statistical analysis, descriptive statistics such as the mean and standard deviation, or median and interquartile range (IQR), will be used for continuous variables. Categorical variables will be reported as frequencies and percentages. To compare independent variables, either the Student’s t-test for independent samples or the Mann–Whitney test will be applied, depending on the distribution of the variables. The chi-squared test or Fisher’s exact test will be used to compare proportions.
Health-related outcomes will be operationalized according to their nature. Cardiopulmonary fitness will be computed as the number of completed laps and maximal oxygen consumption (VO2max) will be estimated according to the following equation (Eq. 1):
VO 2 max = 31.025 + 3.238(speed, km.hr − 1 ) − 3.248(age, yr) + 0.1536(age ⋅ speed) (Eq. 1)
Results of the shuttle run test will be qualitatively interpreted according to normative data provided in Tomkinson et al [41]. Markers of inflammation (IL6, TNF- α) and oxidative stress (TAS, TOS, and OSI) will be operationalized in isolation, and correlations will be explored with other relevant variables such as exposure to ambient pollutants and physical activity volume and intensity metrics. Movement behaviours will be operationalized in isolation and as a composition of 24-hour behaviours, using compositional data analysis (CoDA), as it has been established as a suitable statistical method to study 24-hour movement behaviour composition [42].
To assess the moderating effect of movement behaviours on the association between air pollution and health outcomes, we will test for both additive and multiplicative interactions by including interaction terms in the regression models. Logistic regression models will be used for dichotomous outcome variables, while linear regression models will be employed for continuous outcome variables. The indirect effects of movement behaviours on this association will be estimated using structural equation modelling (SEM) with the R package "lavaan". All models will be adjusted for potential sociodemographic confounders, including the child's age and sex, as well as the parent's socioeconomic status. All statistical analyses will be performed using R software (version 4.2.0, http://www.R-project.org, The R Foundation).
Co-creation process
Based on their availability and interest to participate, a sub-sample of children most exposed to air pollution, plus class teachers, school leaders and parents will be invited to a participatory 3-stage co-creation process, that will be facilitated by the research team. The goal of this process phase is to define solutions to mitigate the exposure of children to air pollutants in their daily lives. The stages will be aligned with the Double Diamond Design Approach (DDDA) by employing divergent and convergent thinking processes, which reflects how the specialists will discover, define, develop, and deliver solutions to the ‘problem’, and how best facilitate real-world implementation [43]. The DDDA is a well-regarded approach within design thinking and has been used in other co-creation research involving children [44]. The process will also observe the four principles of co-creation advanced by Leask and colleagues [45]: planning, conducting, evaluating and reporting.
Prospective participants will be invited to a session where members of the research team will present the co-creation process, including its goals, its different stages and methods, and the role that both participants and researchers will have. Formal informed consent will be requested from participants willing to accept (in the case of children, consent will be requested both to the children and their legal guardians). The first stage of the co-creation process will consist in another session where researchers will share scientific evidence about the health impacts of air pollutants on children’s health. This step will integrate the findings of the previous phase of the project in the co-creation process, and is consistent with the idea that participants have the right to receive information about the evidence base for the health issue being targeted, in order to inform their decisions. Stage two will consist of a participative workshop. Adult stakeholders (class teachers, school leaders and parents) will be divided in smaller groups, which will then engage in various activities in order to develop individual and place level solutions to mitigate the exposure to air pollutants in children´s daily lives. Each group will be engaged in a brainstorming session, generating ideas about the mitigation of exposure to air pollutants in children’s daily lives, corresponding to the “discover” phase of the DDDA. This will be followed be “define” phase: the generated ideas will then be discussed, refined and further developed into proposed solutions. By the end of the session, each group will present its solutions, and participants will vote on the most relevant ones to be included in the proposal. PA, epidemiology, health geography and sociology specialists who conduct the workshop will integrate existing research evidence using creative methods (e.g., post-it note tasks, worksheets, and drawings) to facilitate group´s discussion. To engage the children in the process, without them feeling inhibited in expressing their thoughts in the presence of adults, stage two consists of a similar workshop process with a children´s groups. Stage three, the “develop” phase, consists of a meeting with the whole group to present the solutions that were developed and selected on the two previous co-creation workshops, to hear feedback from all participants and structure a proposal to be published and discussed with decision makers and the schools involved (the final “deliver” phase of the DDDA). Finally, at the end of the session, participants will complete an evaluation questionnaire of the co-creation process. Data collection tools including audio records, observation notes, participant worksheets, and drawings will be used with the intention to illuminate discussion points and allow the participants voices to be represented. Data collected from the co-creation process will be subjected to an inductive thematic analysis, following the Braun and Clarke reflexive thematic analysis approach [46, 47], using NVIVO 14.0.
Major expected outcomes
We hypothesize that: a) children exposed to settings with greater air pollutants concentration will have increased inflammatory markers, oxidative stress and lower cardiopulmonary fitness; b) children less exposed to ambient air pollution will have healthier movement behaviours profile (high PA, sufficient sleep, and minimal sedentary behaviour) and thereby lower inflammatory markers, oxidative stress and better cardiopulmonary fitness; and c) the adverse impact of air pollutants on children´s health are attenuated or absent for those children that are moderately active, with greater sleep duration and quality, and less sedentary. Furthermore, the co-creation process will contribute to increase participants´ awareness and understanding on the topic and their health consequences.
Dissemination
The project´s plan for results dissemination includes both scientific dissemination and science outreach and translation activities to achieve distinct interested groups in a way that all may benefit with the results. Scientific dissemination will be based on publications and presentation of the results at conferences. Along the assessments, the research team will prepare individual reports, translating the results into an easily understandable language to participants, parents, and school staff. Furthermore, we will communicate research evidence in a way that is meaningful to decision makers and the general population. This will be accomplished through the creation of information factsheets and infographics summarizing the most practically impactful project results; TV and radio interviews and social media; press releases of major project results; and open-access publications.