The Internet has become increasingly popular in Japan since the 1990s. The Internet penetration rate in Japan exceeded 75.3% in 2008 [1], and many Japanese people now use the Internet in their daily lives. After the mid 2000s, people began to interact with each other on the Internet using Web 2.0 functions such as blogs, social networking services, and Q&A websites. Web 2.0 is a term that O’Reilly defined as “a set of economic, social, and technology trends that collectively form the basis for the next generation of the Internet, a more mature, distinctive medium characterized by user participation, openness, and network effects” [2]. Users are now able to post comments freely on the Internet without possessing complex technical skills. Hansen [3] stated that Web 2.0 “improved communication and collaboration between people.” Specifically, one of the outcomes of the popularization of Web 2.0 was that people with similar health experiences developed online support communities [4]. On the basis of this standpoint, it is important to determine what people do and how they communicate with each other via the Internet over the course of their illness.

Online communities are beneficial because of their availability; for instance, they have no time restrictions [5] and people can access them from any region at no cost [6]. Thus, it is easy for people with disabilities and psychological burdens to receive support from peers online. Previous studies have shown that patients with heart disease [7] and other rare diseases [8] shared their experiences and exchanged emotional and informational support through online communities. In addition, Hill and Weinert [9] found that online communities help participants learn more about themselves, overcome isolation, and find companionship while adapting to their illness. Thus, online communities are now considered a beneficial peer support resource for patients [10].

Since there are many treatment options for breast cancer, patients’ informational needs are high. In fact, breast cancer is the most common health topic researched on the Internet. Davison et al [11] reported that support related to breast cancer was the most searched-for health topic on the Internet in the United States, followed by acquired immunodeficiency syndrome, alcoholism, and prostate cancer. Sharf [5] observed that patients with breast cancer exchanged information, social support, and even personal empowerment through online communities. Radin [12] found that breast cancer patients promoted “thick trust” and “collected intelligence” through online communities, and that they discussed various typically painful cancer-related topics with candor, warmth, and even humor [13]. Moreover, online breast cancer communities have been shown to be a useful resource in reducing depression [14,15], dealing with cancer-related trauma [16], and improving posttraumatic growth and psychosocial well-being [14]. Online communities have been found to be comparable in effectiveness with face-to-face support groups [16].

People can participate in online communities in two ways. Those who participate actively are known as posters, and those who do so passively, without making any postings, are known as lurkers [17]. van Uden-Kraan et al [18] found that both posters and lurkers are in some way empowered by participating in online communities; they considered this participation to be a form of bibliotherapy.

Previous researchers have identified some of the reasons why people do not post in online communities, including lack software skills, dislike of the group dynamic, or feeling that the community is a poor fit for them [19]. On the other hand, some people simply do not feel the need to post and feel that they are being helpful by not posting [19]. Many previous studies that describe the benefits of online communities have focused on members who actively contributed by posting messages (ie, posters) [18]. However, Nonnecke and Preece [17] reported that in health-related online communities, an average of 45.5% of people participated as lurkers. If online communities are a peer support resource from which even lurkers can gain some benefit, people who feel that it is a technological and psychological burden to post can use these resources more freely.

To provide further evidence of online communities as a health resource, their effects on users’ health should be explored for both posters and lurkers. Moreover, although the Internet penetration rate in Japan is comparable with that of Western countries [20], there have been limited studies of online communities in Japan. Studies of non-English-language online communities are also scarce [21]. Thus, in the present study, we investigated Japanese online breast cancer support communities to determine whether peer support is received differently by lurkers and posters. In addition, we explored the effects of support on members’ mental health between the two groups.

Most of the posters who participated in our study had received a breast cancer diagnosis relatively recently. Notably, this result does not match that of the study of van Uden-Kraan et al [18]. The participants in our survey were all patients with breast cancer, which was different from the samples of previous studies that included patients with chronic disease. Patients with breast cancer are faced with major decisions about their treatment during a short period just after their diagnosis. Thus, in the process between diagnosis and decision making, their informational needs are high and they experience psychological distress [32]. The participants in this study may also have had high informational needs before making major decisions or just after beginning their treatment. Thus, it is possible that patients who have a recent diagnosis may use online communities actively as posters in order to ask questions and express their emotions.

Also in contrast to the study of van Uden-Kraan et al [18], in our study we did not find a significant age difference between posters and lurkers. They attributed this difference to the lack of computer skills of older people. However, in Japan, the penetration of the Internet among people 60 years or older has grown rapidly, from 37.6% in 2008 to 58.0% in 2009, so their familiarity with computers has increased [23]. Thus, in Japan, the difference between posters and lurkers is not thought to be influenced by a lack of computer skills resulting from age. Instead, these differences could be influenced by the level of people’s informational needs, as mentioned above.

In this study, among the 5 functions of peer support from online communities, emotional support and emotional expression were similar to the peer support provided by face-to-face support groups [24]. These were also defined as group cohesiveness and catharsis in online communities [33]. Goodman [31] defined advice, insight, and universality as peer support functions, while Mishima et al [28] and Vilhauer [33] referred to helper therapy as altruism [33]. Moreover, according to Goodman, conflict is considered to be a negative form of support from peers [31].

To put it simply, we ascertained that the 5 support functions found by this survey characterized social support from peers. Additionally, both posters and lurkers were found to receive some amount of support. Social support plays an important role as a buffer for stressful events such as the diagnosis of a life-threatening disease [34]. Online communities are not just convenient for participants because they are accessible 24 hours a day from anywhere; they also act as a beneficial social support resource, even through passive participation (ie, not posting).

Among the 5 functions, insight/universality scored the highest among both posters and lurkers. Therefore, it can be said that the main function of online communities is to provide insight and universality. In our study, scores for emotional support/helper therapy and emotional expression differed significantly between posters and lurkers. So emotional support/helper therapy and emotional expression may be considered to be support that can be received by actively participating in online communities. However, lurkers received a certain amount of these support functions. It can thereby be said that lurkers can feel comforted by online communities, and that they express their emotions without posting because of the modeling effect. People can identify with others more easily by reading or hearing about experiences that are similar to their own [35]; as van Uden-Kraan et al stated [18], lurking in online communities might be seen as a form of bibliotherapy. In addition, lurkers and posters did not have significantly different scores for advice or insight/universality. These results indicate that lurkers, who participate passively, can receive a similar amount of support to that received by posters through active participation.

In this study, the more posters felt they received emotional support/helper therapy and advice, the less anxious they felt. Furthermore, the more advice lurkers gained from their peers, the less anxious they felt. Learning from others who have had similar experiences helps people control their emotions by reducing the number of future unknowns [36-38]. Because our study was cross-sectional, we cannot explain the causal relationship between them. However, theoretically, social support has a positive influence on people’s mental health. Therefore, these associations between received peer support and better mental health may imply that participants reduce their emotional conflict through peer support from online communities. As for advice, people who receive informational support can experience reduced future uncertainty, which can assuage their anxiety. Posters are considered to actively give and receive support, and their actions can positively affect their emotional status. Lurkers can be said to have simulated experiences through reading others’ exchanges in posts.

In our study, the more emotional expression lurkers—who do not express their experiences and feelings directly—received, the less anxious they felt. Iwamitsu et al [39] state that expressing negative and positive emotions appropriately could be beneficial for reducing emotional distress among breast cancer patients. Therefore, our study may partially support his opinion. We found associations between more emotional expression and less anxiety only among lurkers because the lurkers probably read the contents of the online community more carefully than the posters did. It may be easier for lurkers to gain more social modeling effects than for posters, who may not read others’ posts and only post to meet their own needs. Additionally, Silverberg [40] explained the process of bibliotherapy as knowledge about others’ experiences leading to positive outcomes through the mechanism of changes such as insight and catharsis. According to our results, the main function of online communities is to provide insight and universality. Being part of an online community could thereby have a positive effect on mental health. Previously, it was thought that only active participation in online support groups could have a positive effect on mental health [15]. However, this study reveals that online communities may have positive effects for even passive participants as well.

The age group with the most frequent occurrence of breast cancer is women in their 50s [41]. Thus, many patients play multiple roles in their families and careers. It is therefore important to let them know which social support resources can be used with few limitations in terms of time, location, and psychological burden. Moreover, it is important to inform them that these resources may be beneficial for their mental health, even for passive users.