Objective: Diabetes affects the lives of patients and their close relatives. Considering the proven benefit of patient education programs, DiaLife was elaborated as the first German education program addressing the needs of relatives. The objective of this study was to investigate its efficacy.

Methods: The evaluation was implemented in the form of a cRCT with longitudinal design and waiting list condition.In total, 179 relatives were recruited. Participants' diabetes-related knowledge was defined as the primary outcome. Diabetes-related strains, family interaction and other psychosocial factors were determined as secondary outcomes.

Results: A generalized estimating equation model showed a persistent increase of diabetes-related knowledge in the intervention group compared to the control group regardless of the type of diabetes. Concerning secondary outcomes, mixed linear models showed an improvement for relatives of people with type 2 diabetes who participated in the DiaLife program.

Conclusion: This study provides evidence of DiaLife's efficacy regarding a persistent increase of diabetes-related knowledge and a positive effect on psychosocial outcomes in relatives of people with type 2 but not in type 1 diabetes. Adding (an)other psychosocial module(s) might improve their well-being and psychosocial outcomes.

Practice implications: Diabetes centers should consider implementing an education program for relatives, such as DiaLife, in their curriculum.

Trial registration: The study was registered at the German Clinical Trials Register (DRKS00015157; date of registration: 24.08.2018).