An alarmingly low number of children meet public health guidelines for physical activity and dietary behaviours and, therefore, are at increased risk of developing lifestyle-related diseases. This paper describes the protocol of the B-Challenged project, which aims to co-create systemic actions to promote active outdoor play and healthy dietary behaviours before, during or after their outdoor play together with children themselves.

In five European countries, child-centred Participatory Action Research (PAR)—combined with systems dynamics methods—was conducted with 15–20 child co-researchers (aged 9–12 years) and 15–20 adult actors (eg, youth workers, local policy makers). In the first phase, the main drivers of children’s active outdoor play and related dietary behaviours were mapped by (1) analysing existing cohort data, and (2) conducting child-centred PAR. In the second phase, systemic actions targeting the local physical and social environments will be co-created and implemented by child co-researchers and adult actors to promote children’s active outdoor play and related healthy dietary behaviours. A mixed-methods design will be used to evaluate (1) if actions positively contributed to systems change and 6- to 12-year-olds’ outdoor play and related dietary behaviours (140 children per country); (2) the process of conducting multi-actor, child-centred PAR and implementing the co-created actions and (3) if the child-centred PAR positively contributed to child co-researchers’ feelings of empowerment.

Ethics approval for the mapping phase was obtained and approval for implementation and evaluation will be obtained from the five local research institutions. Participating children, one of their parents/caregivers and adult actors had given informed consent before participating in the project. Throughout the project, child-friendly methods, materials and language will be applied, and ethical challenges and potential solutions will be discussed. Project results will be disseminated locally and internationally through various channels and activities among the scientific community, professionals—for example, in health and policy making, children and other citizens.

NCT07136376.

Traditional epidemiological approaches usually assume a constant relationship between cumulative exposure and disease, which implies that exposure duration and intensity contribute equally to the studied outcome. But individuals with the same cumulative exposure but different temporal exposure patterns may show different risks. Trajectory classification is a good way to assess exposure–risk associations and leads to a better understanding of lifetime variability in exposure levels. Therefore, this study aimed to estimate lung cancer risk according to the exposure trajectory classes on welding fumes and cigarette smoking.

Two population-based German case–control studies.

3498 male lung cancer cases and 3539 male control subjects.

Separate latent class mixed models (LCMM) were determined to identify profiles of exposure trajectories of cigarette smoking and occupational exposure to welding fumes. To investigate the risk of lung cancer by class membership, ORs with 95% CI were estimated via multiple logistic regression analyses.

LCMM each identified four latent classes of smoking and welding-fume exposure. Classes of smokers showed much higher risk of lung cancer compared with never smokers or subjects exposed to welding fumes. Smokers in one class characterised with the highest exposure over the past 10 years had the highest adjusted lung cancer risk (OR=39; 95% CI 29 to 53). For welding, the highest lung cancer risks were found for the class in which exposure to welding fumes in the past 10 years prior to the diagnosis of lung cancer was highest and the duration of welding was also quite high (OR=1.71; 95% CI 0.92 to 3.15).

In summary, LCMM opens a new perspective on dose–effect relationships and could be employed to complement established epidemiological methods.