Introduction
Anxiety disorders are a common mental health problem [
1‐
3]. Anxiety disorders are characterized by excessive worry that is difficult to control and can be accompanied by physical symptoms including restlessness, being easily fatigued, difficulty concentrating, irritability, or sleep disturbances [
2,
4]. Women were more likely to experience mild, moderate, or severe symptoms of anxiety than men [
1,
5].
The prevalence of anxiety has increased worldwide. Globally, 45.8 million incident cases of anxiety disorders, 301.4 million prevalent cases and 28.7 million DALYs were estimated in 2019 [
3]. Examples, in each country, over 12% of Thai adults have anxiety symptoms [
6,
7]. In the United Kingdom (UK), the incidence of anxiety symptoms in young adults rose from 6.2/1000 person-years at risk (PYAK) in 2003 to 15.3/1000 PYAR in 2018 [
8]. Terlizzi and Villarro [
5] found that around 15% of adults in the United States experienced symptoms of anxiety. In China, approximately 35% of adults experienced with anxiety symptoms [
9,
10].
Anxiety disorders can have wide-ranging negative effects on adults’ functioning. They are associated with lower cognitive performance [
11] and sleep disturbance [
12], and a high risk of somatic illness such as pain or fatigue [
13]. Additionally, anxiety is related to chronic disease such as GI diseases [
14,
15] and heart disease [
13]. Moreover, having anxiety disorder was associated with a low quality of life [
16], and a lot of limitation in daily living such as social restriction [
17]. Importantly, not only anxiety disorder associated with individuals functioning but also impact to economic burden [
18‐
20]. Anxiety disorder was associated with considerable economic costs owing to lost work productivity and high medical resource use [
20,
21]. As a systematic review and meta-analysis by Konnopka and König [
22] found that an average of direct cost of anxiety disorder corresponded to 2.08% of health care costs and 0.22% of gross domestic product (GDP), whereas indirect cost, on average, corresponded to 0.23% of GDP.
Pharmacologic treatments for anxiety, such as anxiolytics and anti-depressants, have been effective for helping control symptoms of anxiety in adults, but many are not recommended for long-term use. For instance, benzodiazepine and serotonin reuptake inhibitors (SSRIs) are the drugs of choice for the treatment of anxiety. However, chronic use of benzodiazepine can lead to addiction, and abrupt discontinuation of treatment can lead to withdrawal syndrome [
23,
24]. The chronic use of SSRIs can produce side effects such as nervousness, tremors, sweating, nausea, diarrhea, and difficulty falling asleep or frequent awakening [
25].
Non-pharmacologic treatments such as cognitive behavioral therapy (CBT) have been used to treat symptoms of anxiety, but once CBT is discontinued, many patients with anxiety become unresponsive or continue to have residual symptoms [
26]. Additionally, there are several barriers to CBT delivery, such as insufficient therapists [
27]; stigmatization; long waiting times for treatment; and high costs [
28,
29]. Thus, alternative and complementary therapies to improve anxiety symptoms are growing. One of these therapies is mindfulness-based intervention (MBIs).
Mindfulness, is a process that leads to a mental state defined by nonjudgmental awareness of one’s experiences, thoughts, physiological states, consciousness, and environment, while fostering openness, curiosity, and acceptance [
30,
31]. Thus, mindfulness-based intervention (MBIs) is a practice that allows for self-regulation of the body and mind through body scan, sitting meditation and mindfulness movement such as yoga or other mindfulness exercise [
31]. Notable, mindfulness training is recognized as cognitive training because individuals are encouraged to understand the relationship between their thoughts, emotions, and behaviors related anxiety. With this practice, individuals become more aware and can self-regulate their thoughts, emotions, and behaviors related to anxiety [
32]. Mindfulness principles are applied to help individuals in identifying an alternative in mood without immediately evaluating or responding to it. This increased internal awareness is then combined with cognitive therapy techniques which teach individuals to disengage from maladaptive patterns of repetitive thoughts that are associated with anxiety symptoms [
30]. Researchers have shown that using MBIs to treat adults with symptoms of anxiety has fewer barries when compared to other non-pharmacologic treatments and is cost effective [
33]. MBIs refer to a range of therapeutic approaches that guide individuals to use mindfulness techniques, including formal and informal exercises [
31,
34], and emphasizes a non-judgmental focus on and awareness of the present moment [
31]. Formal exercises that facilitate mindfulness include sitting meditation, mindful movement, and body scanning. Informal exercises include mindful eating and are designed to promote mindful awareness in daily activities [
34,
35]. Traditionally, MBIs included a range of formal, daily home-based mindfulness practices informed by mindfulness-based stress reduction (MBSR); mindfulness-based cognitive therapy (MBCT); and adapted mindfulness-based interventions (adapted MBIs). With adapted MBIs, researchers adapted structured sessions of mindfulness-based interventions to be shorter than MBSR and MBCT.
Researchers have conducted meta-analyses on various types of face-to-face and online MBIs to improve anxiety symptoms in the specific population [
36‐
39]. For instance, Lin, Lin [
40] found that MBIs significantly improved anxiety in cancer patients (SMD=-3.48, 95%CI-4.07, -2.88, s = 10). Similarly, Li, Sun [
41] found MBIs could significantly improve anxiety in nursing students (SMD=-0.45, 95%CI, − 0.73, − 0.17,
p = .001). In addition, Spijkerman and Bohlmeijer [
42] found that online MBIs had a small effect on anxiety (SMD = 0.22, 95%CI.05, 0.39, s = 10). Moreover, Witarto et al. [
43] found that online MBIs could improve the severity level of anxiety in adults during the COVID-19 pandemic (g=-0.25, 95%CI, − 0.43, 0.06, p = .008, s = 8). Furthermore, Gong et al. [
44] found that online MBIs had a positive impact to reduce anxiety symptoms in university students (SMD=-0.34, 95%CI, − 0.57, − 0.11, p = .004, s = 6). However, all research teams [
41‐
44] included a small number of primary studies (
s = 5–10), did not specifically included in general adults [
40,
44] and did not examine the subgroup analysis to explore the source of heterogeneity [
40,
41]. Conducting meta-analysis with a small number of primary studies may overestimate the effect sizes [
45,
46].
Importantly, no prior researchers specifically conducted meta-analyses that address the effects of online MBIs on anxiety symptoms and explore the subgroup analysis in the general adult population. Therefore, the purpose of this study was to examine the effects of online MBIs on anxiety symptoms in adult populations. We also explored the moderator effects of source, participants, methods, and intervention characteristics. We hypothesized that adults with anxiety who engaged in online MBIs would have fewer anxiety symptoms than adults who did not engage in online MBIs.
Discussion
This is the first systematic review and meta-analysis exclusively evaluating the effectiveness of online MBIs on anxiety symptoms in adults. Overall, MBIs have a moderate effect (
g = 0.35) on anxiety symptoms in adults compared to control groups. One possible reason might be that with mindfulness practicing, individual pays more attention at the present moment without judgement [
32]. Then, an individual learns how to manage their ruminative thoughts/wondering mind related anxiety [
32]. Our finding is different from a previous published meta-analysis [
42] assessing the effect of online MBIs on psychological outcomes. This meta-analysis found that MBI was small effective in reducing anxiety symptoms (SMD = 0.22, 95%CI.05, 0.39) [
42]. However, they included a small number of primary studies (
s = 10) which might lead to an overestimate of ES [
46] and an inaccurate precision of confidence interval for the common effect size in meta-analysis [
78]. Also, these results were different from our study because their meta-analysis included Internet-based mindfulness treatment (
s = 1), MBSR (
s = 2), MBCT (
s = 2) and ACT (
s = 5). In our study, we only included MBSR, MBCT and adapted MBIs, which are operationalized the mindfulness based on the philosophical perspective of Buddhist teaching using formal meditation as the main interventional component [
79]. We did not include ACT because it relies on the Relational Frame Theory, which is derived from a functional contextualism philosophical perspective and focuses on the behavior of individuals within their historical and situational context [
79,
80]. Therefore, our meta-analysis is novel in that it provides a comprehensive examination of the effect of online MBI on anxiety in adults with a greater number of primary studies (
s = 26) than the prior meta-analysis (s = 10, [
42]. In addition, we conducted moderator analyses, which provide future research directions.
Although gender difference might be a related factor of anxiety disorder [
81,
82], most primary research teams were not report the number of participants in each gender result to a limiting for subgroup analysis to explore how gender affects to the ES. Thus, we recommend the primary researchers address the number of participants based on gender.
Attrition rate is considered a factor affecting the online MBIs’ effect. We found that when the attrition rate increased, the effects of online MBIs was reduced, indicating an increase in anxiety scores. Since a higher attrition also results in a smaller number of participants in the analysis, the precision of the effect size is reduced [
46,
83,
84]. We recommend that future researchers account for attrition during recruitment of participants.
Strengths and limitations
Ours was the first systematic review and meta-analysis of online MBIs on anxiety symptoms in adults. We did a moderator analysis on the biggest number of primary studies (s = 26) to date. Yet, there are certain drawbacks to this meta-analysis. Initially, we limited our search to main research written in English; relevant studies written in other languages would have been missed. Researchers in the future should incorporate papers published in different languages. Second, due to insufficient data reporting, we did not investigate the impact of several key parameters on the effect magnitude. For example, most researchers did not consider intervention fidelity, which was a constraint for investigating this characteristic that influences effect magnitude. Lastly, most investigations examined outcomes shortly after the intervention was completed (s = 19); long term effects were not measured. Thus, more long-term MBIs studies on anxiety symptoms in adults are needed.
Implications and recommendations
This systematic review and meta-analysis provides evidence for the use of online MBIs in adults with anxiety. Specifically, nurses and health professionals might consider using online MBIs as an adjunctive or alternative complementary treatment to improve anxiety, especially when there are insufficient mental health professionals. Electronic services such as online MBIs might benefit adults who are concerned about negative perceptions of anxiety treatment. Researchers should explore the long-term effects of online MBIs on anxiety in adults. Finally, researchers should account for attrition during the recruitment of participants.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.