Table 3. Overview of findings for outcomes of interest, comparing intervention groups who engaged with volunteers with a control condition.

Outcome Type	Favors Volunteer Intervention Group	No Difference between Groups
Psychosocial	Perceived social support (MSPSS) [52]	Depression (PHQ-2) [50] Depression (PHQ-9) [49, 55] Diabetes distress (DDS) [50, 55] Diabetes quality of life (ADDQol) [51] Diabetes self-efficacy (DES-20) [49] Diabetes-related distress (CDDS-15) [49] Emotional distress (PAID) [53] Empowerment (DES-SF) [53] Oral-health quality of life (OHIP-14T) [48] Perceived diabetes-specific social support (DSS) [47] Psychological distress (DASS-21) [49] Psychological wellbeing (GHQ-12) [52] Quality of life (EQ-5D) [49, 51] Quality of life (WHOQOL-BREF) [54] Well-being (WBQ-12) [51]
Behavioural	Attitudes towards periodontal health [48] DBQ fat score scale at 24 months [51] Oral health-related knowledge [48] Oral self-care behaviours [48] Physical activity weekly duration & frequency (PASE) [52] Steps (pedometer) [52]	Medication adherence [49] Physical activity (IPAQ, resistance questionnaire) [51] Self-care behaviours (SDSCA) [49, 53]

Abbreviations: ADDQol = Audit of Diabetes Dependent Quality of Life; CDDS-15 = Chinese Diabetes Distress Scale-15; DASS-21 = Depression Anxiety Stress Scale-21; DBQ = Dietary Behaviours Questionnaire; DDS = Diabetes Distress Scale; DES-20 = Diabetes Empowerment Scale-20; DES-SF = Diabetes Empowerment Scale-Short Form; DSS = Diabetes Support Scale; EQ5D = EuroQol-5D; GHQ-12 = General Health Questionnaire-12; IPAQ = International Physical Activity Questionnaire; MSPSS = Multidimensional Scale of Perceived Social Support; OHIP-14T = Oral Health Impact Profile-14; PAID = Problem Areas in Diabetes; PASE = Physical Activity Scale for the Elderly; PHQ-2 = Patient Health Questionnaire-2; PHQ-9 = Patient Health Questionnaire-9; SDSCA = Summary of Diabetes Self-Care Activities; WBQ-12 = Well-Being Questionnaire-12; WHOQOL-BREF = World Health Organization Quality of Life Scale