Interventions to improve oral health and related health behaviours of substance use, smoking, and diet in people with severe and multiple disadvantage: a systematic review of effectiveness and cost-effectiveness.

Background: Homelessness overlapping with substance use and offending is described as severe and multiple disadvantage (SMD). People experiencing SMD have poor oral health along with high levels of related behaviours such as substance use, smoking, and poor diet. Existing evidence largely describes the prevalence of oral health problems, substance use, and smoking in SMD groups. Little is known about interventions that can address these conditions in SMD groups. We aimed to review the effectiveness and cost-effectiveness of interventions on oral health and related health behaviours in adults experiencing SMD.
Methods: For this systematic review, we searched bibliographic databases (MEDLINE, EMBASE, PsycINFO, CINAHL, EBSCO, Scopus) and grey literature for papers published from inception to February 2023. Two researchers independently reviewed the searches. Randomised controlled trials (RCTs), comparative studies and economic evaluations were included. Risk of bias was assessed. Population included adults experiencing SMD (including homelessness and substance use or repeat offending). Outcomes included oral health, and related behaviours (substance use, smoking, poor diet). Results were narratively synthesised. This review was registered with PROSPERO, CRD42020202416.
Findings: The review included 38 studies (published between 1991 and 2023), with 34 reporting effectiveness. These studies comprised of 23 RCTs and 11 quasi-experimental studies conducted in the USA (25 studies), Canada (seven studies), France (one study), and Spain (one study). The interventions involving multiple components, such as housing services with substance use and mental health support, effectively reduced substance use in SMD groups; these were mostly individual-level interventions. However, these studies had short follow-up periods and high attrition rates. Only one study addressed oral health outcomes, none focused on diet, and three RCTs covered smoking, with one intervention showing smoking abstinence at 4 weeks. Some limited evidence suggested cost-effectiveness of substance use interventions.
Interpretation: This review found that integrating services such as housing with other health-care services together could be effective in improving health behaviours, especially substance use among SMD groups. More evidence is needed specifically on oral health, smoking, and diet-related interventions. The generalisability of findings of this review is limited to high-income countries and shorter-term outcomes.
Funding: National Institute for Health and Care Research (NIHR) Policy Research Programme.
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