From the searches between January 2002 and February 2012, the selected studies in this review were published from 2007 to 2012 with the vast majority in the last 2 years (Table 1). From the available methodology of bias tools/quality scales, the Downs and Black Instrument [123] has been previously identified as a recommended tool to evaluate the quality of both quantitative randomized and nonrandomized studies [124]. As there are no standard accepted quality scales for studies of proportions [125], only quantitative studies (including mixed methods) were evaluated. Using this Downs and Black instrument [123], the maximum total score that could be achieved was 32, but the scores of the studies in this review ranged from 3 [89] to 22 [121]. Overall, the studies scored low using this scale as they were mainly exploratory and descriptive with three intervention studies [43,112,121] and one randomized controlled trial (RCT) [45]. From the 98 studies, 40 were applied quantitative, 48 qualitative (including studies with content analysis presenting data with descriptive statistics), and 10 mixed methods (both quantitative and quantitative). These studies are presented by methodology in Table 2. Methodological bias of the selected studies using the Downs and Black instrument [123] is presented in Multimedia Appendix 3.

The characteristics of users of social media for health communication in the selected studies were diverse, covering a range of different population groups. The age of the social media users ranged from school children to older adults aged 65 years and up [24-121], but the majority of the reported ages were 11-34 years [25,35,45,46,64,77,104,107,119]. Some studies reported that there were more female than male users of social network sites [35,40,55,62,64]. A few studies found that social media users were disproportionately from lower-income households [35,64,72]. Studies within the United States reported that more social media users were African Americans than nonHispanic Whites [35,40]. Chou et al [35] concluded that the population is accessing social media regardless of education and race/ethnicity.

From the selected studies, seven key uses of social media for health communication were identified for the general public, patients, and health professionals (Table 3). Social media provided health information on a range of conditions to the general public [36,61,71,74,103], patients [47,63,71,75,98,103], and health professionals [36,47,98]. This communication can provide answers to medical questions [34,36,60]. Social media allows information to be presented in modes other than text and can bring health information to audiences with special needs; for example, videos can be used to supplement or replace text and can be useful when literacy is low [50]. A range of social media platforms can facilitate dialogue between patients and patients, and patients and health professionals [56,79,110]. Sites such as PatientsLikeMe enable patients to engage in dialogue with each other and share health information and advice including information on treatment and medication [28,75]. YouTube has been used by the general public to share health information on medications, symptoms, and diagnoses [38], and by patients to share personal cancer stories [80]. Blog sites create a space where individuals can access tailored resources [26] and provide health professionals with an opportunity to share information with patients and members of the public [30,56]. Facebook is being used by the general public, patients, carers, and health professionals to share their experience of disease management, exploration, and diagnosis [37]. Asthma groups are using MySpace to share health information, in particular personal stories and experiences [49,60]. Social media can be used to collect data on patient experiences and opinions such as physician’s performance [26,65,109].

Social media have been used for health promotion and health education [25,34,46,59,82,90,113,117] and for delivering a health intervention by providing social support/influence to promote smoking cessation and abstinence [55]. A study has shown that social media can reduce stigma about certain conditions such as epilepsy [67]. In addition, there were some opportunities for health professionals to have online consultations [88].

Six overarching benefits of social media for health communication were identified for the general public, patients, and health professionals (Table 4). Social media users have the potential to increase the number of interactions and thus are provided with more available, shared, and tailored information. Social media can generate more available health information as users create and share medical information online [50]. Blog sites create a space where individuals can access tailored resources to deal with health issues [26]. Social media can widen access to those who may not easily access health information via traditional methods, such as younger people, ethnic minorities, and lower socioeconomic groups [35,64,66,83,84,86,99,104,107,115]. An important aspect of using social media for health communication is that it can provide valuable peer, social, and emotional support for the general public [37,43,44,47,48,51,56,73,101,108,114] and patients [28,33,34,44,47,48,56,60,62,68,71,76,88,98,120]. For example, social media can aid health behavior change such as smoking cessation [53,73], and PatientsLikeMe enables patients to communicate with other patients and share information about health issues [28]. Colineau and Paris [56] reported that people used health-related social networking sites to discuss sensitive issues and complex information with health professionals.

In public health surveillance, social media can provide communication in real time and at relatively low cost [31,40,54,57,72,111,116]. Social media can monitor public response to health issues [54], track and monitor disease outbreak [111], identify misinformation of health information [72], identify target areas for intervention efforts [106], and disseminate pertinent health information to targeted communities [57]. Health professionals can aggregate data about patient experiences from blogs and monitor public reaction to health issues [26,40]. Social media may have particular potential for risk communications as they can be used to disseminate personalized messages immediately thus making outreach more effective [58]. There is the potential that information on social media may contribute to health care policy making, as medical blogs are frequently viewed by mainstream media [29].

There were 12 limitations of social media for health communication (Table 5). The main recurring limitations of social media are quality concerns [26,39,42,44,47,50,69,85] and the lack of reliability of the health information [26,37,39,40,42,44,47,50,69,74,85,95]. The authors of websites are often unidentifiable, or there can be numerous authors, or the line between producer and audience is blurred [38,50,74]. Thus it is more difficult for individuals to discern the reliability of information found online [50,38]. Regulations may not facilitate health professionals to communicate with patients online, for example, email is not an official medical record and could be vulnerable to security breaches [68]. Policy reactions to address concerns include providing training in how to use and navigate social media technologies and validate accuracy of information found [39,66], or bringing more credible sites into the mainstream and making them fully accessible [39].

The large volume of information available through social media and the possibility for inaccuracies posted on these sites presents challenges when validating information [26]. Several studies highlighted concerns about privacy and confidentiality, data security, and the potential harms that emerge when personal data are indexed [38,44,47,50]. Social media users are often unaware of the risks of disclosing personal information online [26] and with communicating harmful or incorrect advice using social media [26,50]. As information is readily available, there is the potential of information overload for the user [50]. The general public may not know how to correctly apply information found online to their personal health situation [50]. There is the potential that adverse health consequences can result from information found on social media sites, for example, pro-smoking imagery [24]. In addition, there may be negative health risk behaviors displayed online, such as unsafe sexual behavior [45,46]. There is limited evidence that engaging in online communities positively impacts people’s health [56]. Health professionals may not often use social media to communicate with their patients [42]. There is also the possibility that social media may act as a deterrent for patients from visiting health professionals [42].

The main uses of social media focus on increasing interactions with others, and facilitating, sharing, and obtaining health messages [24-121]. The general public mainly use social media for themselves, family members, and/or friends to obtain and share information on a wide range of health issues [36,60,61,71,74,103]. Patients can share their experiences through discussion forums, chat rooms and instant messaging, or online consultation with a qualified clinician [26,62,63]. Some health professionals were reported to use social media to collect data on patients [26,65] and to communicate with patients using online consultations [88]; however, this latest use is limited. Recent research reported that female health professionals in Quebec, Canada, believed that Web 2.0 may be a useful mechanism for knowledge transfer but is limited due to their lack of time and technological skills [126]. Perhaps in light of Kaplan and Haenlein’s [10] classifications of social media, further work on improving the “social presence”, the closeness to synchronous face-to-face communication of such online consultations, would contribute to improving communication between health professionals and patients. Another recent study applied social network analysis to understand the knowledge sharing behavior of practitioners in a clinical online discussion forum and found that although their number is limited, interprofessional and interinstitutional ties are strong [127]. This relates to Gilbert and Karahalios’ [128] social tie analysis and suggests that development of mechanisms that evaluate tie strength in social media that in turn impact on its functionality may be useful for health communication. Further technological advances will provide more opportunities to use social media in health care in the future, especially between patients and patients, and also health professionals and patients. However, both patients and health professionals may require training to fully maximize the uses of using social media in health care.

Numerous benefits of using social media for health communication were reported for the general public, patients, and health professionals. A major benefit of social media for health communication is the accessibility and widening access of health information to various population groups, regardless of age, education, race or ethnicity, and locality, compared to traditional communication methods [35,64,95,72]. While these changing patterns may lessen health disparities, traditional inequalities in overall Internet access remain. Furthermore, variation in social media engagement according to personality traits, age, and gender [15] suggests the need for ongoing scrutiny regarding equality of access and effectiveness for different users. Social media can be used to provide a valuable and useful source of peer, social, and emotional support to individuals, including those with various conditions/illnesses [48,62,71]. Hwang and colleagues [62] reported that encouragement, motivation, and shared experience were important social support features of social media sites.

Social media allows users to generate peer-to-peer discussion in a way not enabled by traditional websites [48,50,62,71]. However, this may challenge expectations, relationships, quality, and consistent health care practice. As Moen et al [44] explain, current patterns of collaboration tend to produce an asymmetric patient-health care provider relationship. This highlights a strong need for health providers to maintain a role within social media health communication that is not simply the same as that of patient and general public users. Keitzmann et al [17] have suggested that organizations need to recognize and understand the social media landscape, and where the conversations about them are already being held (cognize), develop strategies that are suitable, work out how often and when they should enter into conversations, and be aware of what others are doing and act accordingly. This review highlights clearly that social media has benefits for health communication but the long-term effects are not known. As the use of social media is expected to increase in the future [1], there may be further benefits of using social media in health care. It is not yet known how effective social media applications are in health communications, which warrants further research.

Social media tools remain informal, unregulated mechanisms for information collection, sharing, and promotion, so the information is of varying quality and consistency [26,27,39,40,42,44,47,50,69,74,85,95]. Similar issues exist with traditional Internet sites, but these issues are being heightened by the interactive nature of social media, which allows lay-users to upload information regardless of quality [50]. Reliability may be monitored by responsible bodies using automated processes, employed to signal when content has been significantly edited, and progress is being made in automated quality detection [50]. Further work to improve the “media richness” [10] of social media for health communication, that is, how they may reduce ambiguity and uncertainty, would be valuable. In addition, combining more resources in one site could improve reliability of information. As patients interact and share links, they could compare numerous social media sites and triangulate information to help them discern correct from incorrect information [50]. Despite concerns, information found on some websites is reported to be generally factually accurate [39,62]. A further limitation is that postings can be a permanent record and be viewed by an increasing audience, and perhaps users are unaware of the potential size of the audience base. Regulatory and security issues must be addressed to broach a way forward for best-practice that allows the benefits of social media to be utilized yet still protects patients’ privacy and to therefore improve use of these media in routine clinical care. This is a public policy issue and is already being contested in the United States. Public education is required for the general public, patients, and health professionals to make them more aware of the nature of using social media. Consideration of the variation in social media engagement according to personality traits, age, and gender [15] will be valuable in tailoring education to meet the needs of population groups.

This literature review has shown that the general public, patients, and health professionals use social media in health care for various purposes with numerous benefits and limitations. The current research’s methodological scoring was low; this was mainly due to the fact that the vast majority of the studies in this review were exploratory and descriptive. To date, there is very limited evidence from RCTs and longitudinal studies. To more fully determine the role of social media for health communication, further research with larger sample sizes and more robust methodologies are required. Based on this review [24-121], several gaps in the literature have been identified that need to be addressed:

To address these gaps in the literature, the key recommendations for future health communication research focus on robust and comprehensive evaluation and review, using a range of methodologies. The research priorities are highlighted below:

Social media brings a new dimension to health care, offering a platform used by the public, patients, and health professionals to communicate about health issues with the possibility of potentially improving health outcomes. Although there are benefits to using social media for health communication, the information needs to be monitored for quality and reliability, and the users’ confidentiality and privacy need to be maintained. Social media is a powerful tool that offers collaboration between users and a social interaction mechanism for a range of individuals. With increasing use of social media, there will be further opportunities in health care. Research into the application of social media for health communication purposes is an expanding area because increasing general use of social media necessitates that health communication researchers match the pace of development. Further robust research is required to establish whether social media improves health communication practices in both the short and long terms.