Background:
Health literacy comprises the ability to identify, obtain, interpret and act upon health information. Low health literacy is a major risk factor for morbidity, premature mortality, and increased use of emergency care. Systematically developing interventions to increase health literacy using effective techniques is an important public health task. The aim of this systematic review therefore is to summarize interventions to increase health literacy in socioeconomically disadvantaged groups and identify the most effective techniques.

Methods:
Following PRISMA guidelines, we searched the databases SCOPUS, Pubmed, Web of Science and CINAHL. We included intervention studies with a quantitative study design and a control group aiming to promote health literacy or health knowledge in socioeconomically disadvantaged populations between 18 and 65 years. Where possible, we converted effect sizes into cohen´s d and compared mean differences of intervention and control groups. Using p-values, sample sizes and effect sizes we created albatross plots to summarize the results according to different outcomes (health knowledge on childfeeding and maternal nutrition, diabetes, food, cancer screening, functional health literacy, HIV knowledge, mental health literacy).

Results:
We screened 3696 titles and abstracts and 206 full-texts. In total, 86 articles were included of which 57 were summarized in seven albatross plots. The majority of the studies had a randomized controlled study design (n=50). More effective intervention approaches used focus group discussion prior to intervention, used multilingual educational materials and included professionals as intervention deliverers who were fluent in the first languages of the study population. Additionally, the use of educational materials in video, and text form, fotonovelas and interactive group education sessions with role playing exercises were effective as well.

Conclusion:
Effective interventions to improve health literacy and knowledge in socioeconomically disadvantaged populations should take into account the background of participants, use multiple languages and if possible professional intervention delivery personnel.