Table 2.

Characteristics of included reviews

Review	Scope of the review	Search dates	Number of included studies	Population	Exclusion criteria for participants	Criteria for volunteering	Coding of outcomes assessed	Meta-analysis	AMSTAR 2 rating
Anderson et al. (2014)	The benefits of volunteering for older adults and build a theoretical model of how volunteering reduces risk of developing dementia	Inception up to April 2014	73	Mostly based in the USA and Canada, aged between 41 and 93	Older adults aged 50 or over	Formal volunteering	Psychological Physical Social General	No	− 10
Blais et al. (2017)	The benefits of intergenerational volunteering by students and residents of long-term care homes	Not provided	5	Based in the USA and Canada, mostly university students	High school or postsecondary volunteers, working with older adults residing in long-term care homes	Volunteering inside the long-term care homes and involved direct contact with the residents. Excluded service learning	Social	No	− 18
Cattan et al. (2011)	The impact of volunteering on older volunteers’ quality of life	Between 2005 and 2011	21	Mainly based in the USA and included participants from either the age of 55 or 65 years	Older adults aged 50 years or over	Formal volunteering	Psychological Physical General	No	− 10
Chen et al. (2020)	The benefits, motivations and drawbacks of environmental volunteering in older adults	Inception to July 2020	9	SS of 328, most based in Taiwan or the USA. Mean age ranged from 65.6 to 75.7	Older adults	Volunteering with an intention to improve the outdoor environment	Psychological Physical Social General	No	9
Conway et al. (2009)	Changes associated with service learning and moderators of these changes	Inception to June 2008	103	SS of 1,819 for self-evaluations, and 274 for well-being	None	Service learning	Psychological General	Yes	− 20
Farrell & Bryant (2009)	Volunteering to promote social inclusion for volunteers with mental health problems	Not provided	14	Mainly based in the UK or USA, range of subpopulations (e.g. people with disabilities)	Participants with mental health problems	Volunteering to promote social inclusion	Psychological Social General	No	− 15
Filges et al. (2020)	The effects of volunteering on physical and mental health adults aged over 65	Inception to December 2018, more searches carried out in September and October 2019	90 (26 for this data synthesis)	Average SS of 2,369 for volunteers, and an average of 61% female. Mostly from the USA, average age of 76 for volunteers	Older adults aged 65 or over	Formal volunteering in comparison to non-volunteers	Psychological Physical General	Yes	30
Galbraith et al. (2015)	The goals, characteristics, and outcomes of intergenerational programmes for children or youth and people with dementia	Inception to February 2014	27	No information (only studies were of volunteering)	People with dementia and participants aged under 19	Dementia specific intergenerational programmes	Psychological	No	− 10
Giraudeau & Bailly, 2019	Characteristics, definition, and benefits of intergenerational programmes for school-aged children and adults aged above 60 years	2005–2015	11	SS ranged from 11 to 46 for older volunteers, mostly based in the US	Older adults aged 60 or over and school-aged children	Intergenerational programmes	General	No	− 6
Goethem et al., (2014)	The general, academic, personal, social, and civic outcomes of community service, and their moderators including reflection	1980 and September 2012	49	No information	Adolescents between 12 and 20 years old without a mental disability	Volunteering, community service, and service learning	Psychological Social	Yes	− 4
Gualano et al. (2018)	The effects of intergenerational programmes on elders and children, and the key elements that determine their success	Not provided	27	SS of older adults ranged from 6 to 162, based mostly in the USA followed by Japan	Older adults and school or pre-school children	Intergenerational programmes	Psychological Physical Social General	No	9
Höing et al. (2016)	To support the development of policy and selection of volunteers working with medium to high risk sex offenders	1999 to October 2012	50	Most either focused on adults in general, or older adults aged 55 or over	For volunteering with sex offenders: working with sec offenders with the aim of reducing the behaviour	Volunteering in general and volunteering for medium to high risk sex offenders	Psychological Physical Social General	No	− 7
Howard & Serviss (2022)	Benefits of corporate volunteering programmes, and whether individual or organisational-level participation is most beneficial	Inception to May 2020	57	No information	Individual or organisational level	Corporate volunteering programmes	Psychological General	Yes	− 1
Hui et al., (2020)	Strength of the prosociality to well-being link under different conceptualisations, and their moderators	Inception to April 2014, more searches conducted in December 2016 and September 2019	126	No information	Adults 18 or over	Prosociality variables (including volunteering)	General	Yes	− 12
Hyde et al., (2014)	Benefits of episodic volunteering	Inception to April 2014	41 overall (20 within health and social welfare)	Mostly based in North America, most common age range was 30–60, mostly Caucasian, married, employed, and of middle income	None	Episodic volunteering outside of disaster settings and within one’s country (once or on a seasonal or annual basis)	Social	No	− 2
Jenkinson et al., 2013	Benefits of formal volunteering for physical and mental health and survival, and the influence of volunteering type and intensity	Inception to January 2013	40	Mostly based in the USA and North America and recruited those 50 years or over. Total SS of 308 for RCTs and 307 for NRCTs, and most cohort studies recruited samples over 1000	Adults aged 16 or over	Formal volunteering (sustained and regular: over 1 h twice monthly)	Psychological Physical General	No	17
Kragt & Holtrop (2019)	Characteristics, motivations, benefits, psychological contract, commitment, and withdrawal of volunteering in Australia	Inception to August 2018	152 (it total, on all aspects of volunteering)	All based in Australia	Participants in Australia	None	Psychological Social General	No	− 15
Lovell et al. (2015)	Impact of participation in environmental enhancement and conservation activities on health and well-being	Inception to October 2012	23 (13 with quantitative data)	Mostly based in the UK with samples aged between 40 and 60. SS ranged from 3 to 2630	None	Volunteering: outdoor and physically active environmental enhancement or conservation	Psychological Physical Social General	No	0
Manjunath & Manoj (2021)	Effectiveness of interventions to decrease social isolation in older adults	No information	20	2 studies eligible for volunteering; 1 international, the other based in Sweden	Adults aged 50 or over	Interventions to reduce isolation targeted towards older adults experiencing loneliness (included volunteering)	Psychological	No	− 11
Marco-Gardoqui et al. (2020)	The academic, personal, and social impact of service learning on students in business schools	Inception to October 2019	32	Mean SS of quant studies was 228. Mostly based in the USA. No first year students	Business students	Service learning	Psychological Social	No	5
Milbourn et al. (2018)	The relationship between time spent volunteering and quality of life in adults aged over 50	January 2000 to April 2014	8	SS ranged from 180 to 4860, mostly based in the USA, women, Caucasian, with a variety of income and education levels	Adults aged 50 or over	Time spent volunteering	Psychological Physical Social	No	− 8
O’Flynn et al. (2021)	The motivation and benefits of volunteers in inclusive watersports	Not provided	8 for benefits	No information	None	Volunteers in sport or disability inclusion	Social General	No	− 14
Okun et al. (2013)	The relationship between organisational volunteering and mortality in adults aged over 55	Inception to November 2011	13	Mainly based in the USA. SS ranged from 868 to 15,938. Median age was 66.5 years	Older adults	Organisational volunteering	General	Yes	− 9
Onyx & Warburton (2003)	To investigate the relationship between volunteering and health among older people	Not provided (searched last 10 years)	25	Developed countries, mostly the USA and Australia	Older adults	Volunteering	Psychological Physical General	No	− 22
Owen et al., (2022)	The effectiveness of purposeful activity on well-being and quality of life outcomes in ‘oldest old’ adults (aged over 80)	Inception to April 2020	8 (5 for volunteering)	Mostly from the USA, SS ranged from 10 to 88	Older adults with a mean age of 80 or above	Purposeful activity (divided into volunteering and learning a new skill)	Psychological General	No	5
Bonsdorff & Rantanen (2011)	The relationship between formal volunteering and well-being for older volunteers and the people they serve	Inception to November 2009	16	All based in the USA. SS ranged from 705 to 7496 for prospective studies, the SS for the included RCT was 128. Ages ranged between 60 and 97 for the prospective studies, mostly women and White, and were more highly educated and were of better perceived health than non-volunteers	Adults aged 60 or over	Volunteering in visits or within a timeframe	Psychological Physical General	No	-14
Wheeler et al (1998)	The effectiveness of volunteering for older adults and the people they serve	No information	37 (30 for outcomes of volunteers)	SS ranged from 15 to 2164 (median 98), mostly based in the USA. Average age was 71, mostly White (90%) and female (72%)	Older adults	All forms of volunteering	Psychological	Yes	− 17
Willems et al. (2020)	The mental well-being of crisis line volunteers and moderators	Inception to November 2018	13	SS ranged from 28 to 216 for the quantitative surveys. Sample were a range of ages and mostly female	Crisis line volunteers	Volunteers from a crisis line or chat line	Psychological Social	No	1