Findings from psychotherapy research demonstrate that most of the improvement takes place in the initial phase of treatment, and the degree of improvement is linearly associated with the time spent in psychotherapy (Nordmo et al., 2021), suggesting a dose-response effect in psychotherapy. Recently a systematic review for the dose-response effect in routinely delivered psychological therapies found that there was a curvilinear relationship between treatment length and outcome. In that review of 26 studies, optimal doses of psychotherapy in routine settings ranged between 4 and 26 sessions, and varied according to setting, clinical population, and outcome measures. Weekly therapy appeared to accelerate the rate of improvement compared to less frequent schedules (Robinson et al., 2020). For low intensity psychological interventions (guided self-help and psycho-education using cognitive behavioral therapy principles), at least four therapy sessions are necessary to achieve more than 50% reliable and clinically significant improvement (RCSI) rates on depression or anxiety, and the dose-response effect appears to decline in treatments longer than six sessions (Delgadillo et al., 2014). Although there is some evidence of a dose-response effect of psychotherapy, the number of studies which address dose–response relationships are few (Cuijpers et al., 2019).

Over the past few decades Mindfulness-Based Interventions (MBIs) have become one of main psychotherapies in the treatment of mental disorders (Goldberg et al., 2018). MBIs provide patients with mastery of objective observation, awareness, and acceptance. Mindfulness-Based Cognitive Therapy (MBCT) is a form of MBI that combined mindfulness with cognitive behavioral techniques to reduce emotional reactivity (Williams et al., 2008). Evidence suggests that MBCT is effective at reducing the symptoms of depression, anxiety and preventing relapse in populations that are more at risk for depression (Kuyken et al., 2016).

Meta-analyses have demonstrated that proinflammatory cytokines were increased in MDD patients (Köhler et al., 2017). MBIs have shown to be effective in decreasing levels of low-grade inflammation markers. The levels of tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) were significantly decreased from baseline to post-intervention in depressed adults after MBIs when compared to controls (Hoge et al., 2018). Brain-derived neurotrophic factor (BDNF) is a neurotrophin that plays a vital role in neuron survival, growth, and maintenance in brain circuits relating to emotional and cognitive function (Phillips, 2017). Accumulating evidence shows that neuroplastic mechanisms dependent on BDNF are deleteriously changed in MDD (Lorenzetti et al., 2020). Recently a study showed that MBCT combined with pharmacotherapy could improve patients’ psychological state, compliance and increase the serum level of BDNF in preventing the recurrence of depression (Guo et al., 2022).

MBIs are effective for the treatment of common mental health problems, but the dose-response effect of MBIs remains unclear when understanding of the psychotherapy, including the web-based formats of MBCT (Edenfield and Saeed, 2012; Segal and Walsh, 2016), such as the number of sessions, the training time of home work. In our previous study, internet-based Mindfulness-based Stress Reduction (iMBSR) showed efficacy in reducing psychological symptoms among survivors of breast cancer (BC). For survivors of BC, iMBSR practice had a potential dose–response efficacy, with a threshold of > 30 minutes daily practice for optimal symptom reduction (Kang et al., 2021). Recently another randomized controlled trial (RCT) study found that MBCT was effective for college students with MDD, and the efficacy was positively related to the session numbers of intervention and daily practice time (Xu et al., 2023). Although the two studies had consistent results, there are certain problems, especially the lack of proper controls. Therefore, in the present study we explored the dose-response effect of MBCT in a RCT trial by compared the MBCT group to a wait-list (WL) group of MDD undergraduate students with the aim to better understand the dose-response effect in MBCT. We hypothesized that MBCT group would be superior to a waitlist control condition, and that there is a dose-response effect of MBCT. To the best of our knowledge, this 8-week RCT is the first to investigate the dose-response effect of MBCT on the improvement of MDD.