Inequalities in exclusively mobile interventions targeting weight-related behaviours: Systematic review of observational studies

Background: Mobile health interventions are promising behaviour change tools, but they might benefit deprived populations less. Evidence so far mainly stems from analyses of clinical trial data, which may suffer from selection bias. This systematic review investigated differences in uptake of, engagement with, and effectiveness of exclusively mobile interventions for diet, physical activity, and sedentary behaviour (i.e., weight-related behaviours) in adults and in real-life contexts. Methods: Five databases (CINAHL, EMBASE, PsycINFO, PubMed, Web of Science) were searched from inception to November 2023. Records were independently screened by two authors. Observational studies including adults were considered if they reported on uptake, engagement, and/ or effectiveness of an exclusively mobile intervention, and examined outcomes by at least one inequality indicator included in the PROGRESS-Plus framework. Risk of bias was assessed with a tool for observational studies provided by the NIH.Results: Of the 9707 identified records, 87 publications reporting on 88 studies were included. Most studies reported on intervention uptake (k = 53) and examined multiple inequality indicators, with the majority studying age (k = 74) or gender/ sex (k = 79). Furthermore, studies investigated indicators of socio-economic position including education (k = 41) and income (k = 26). Younger age and higher socio-economic position were mostly associated with increased uptake, although these differences did not translate to engagement or effectiveness. Results for other inequality indicators were mixed, and some (e.g. migration [k = 4], sexual orientation [k = 1]) were rarely studied.Conclusions: Evidence regarding a digital health divide remains mixed, although some barriers to the uptake of mobile interventions, such as access to the required technology and digital literacy exist. Research urgently needs to address potential inequalities beyond age, gender/sex and socio-economic position to ensure that mobile interventions do not widen existing health inequalities.Registration: The protocol was registered on PROSPERO (CRD42021290769).