Effectiveness of Mindfulness-based interventions on physiological and psychological complications in adults with diabetes: A systematic review

Abstract

This systematic review aimed to examine the effectiveness of Mindfulness-based interventions in reducing diabetes-related physiological and psychological symptoms in adults with types 1 and 2 diabetes. Five databases were systematically searched. A total of 11 studies satisfied the inclusion criteria. Mindfulness-based intervention effectiveness for physiological outcomes (glycaemic control and blood pressure) was mixed. Mindfulness-based interventions appear to have psychological benefits reducing depression, anxiety and distress symptoms across several studies. Studies’ short-term follow-up periods may not allow sufficient time to observe physiological changes or illustrate Mindfulness-based interventions’ potential long-term efficacy. More long-term studies that include a consistent, standardised set of outcome measures are required.

Keywords

diabetes mindfulness mindfulness-based cognitive therapy mindfulness-based stress reduction systematic review

Introduction

Diabetes is a chronic metabolic disease that can lead to glycaemic, neuropathic, nephropathic, retinopathic and macrovascular complications (Fowler, 2008; Porte and Schwartz, 1996). Although the physical symptoms of diabetes are well documented, patients with the disease must contend with more than just these symptoms. Diabetes is psychologically and behaviourally demanding, as it requires meticulous self-management through multiple simultaneous lifestyle adaptations. To manage their disease, people with diabetes must monitor their physical activity levels, diet, weight, medication requirements and blood glucose levels.

As such, diabetes presents a considerable source of life stress. Thus, it is not surprising that diabetes has a high comorbidity with some psychological disorders. People with diabetes are twice as likely to have depression at clinical levels (Anderson et al., 2001). Additionally, 40 per cent of patients with diabetes exhibit elevated anxiety symptoms (Grigsby et al., 2002). Diabetes also presents a social burden that can impede social interactions, as people with diabetes often perceive negative appraisal of their condition by others (Schabert et al., 2013). Schabert et al. outlined various aspects of negative appraisal that emanate from higher body weight and use of insulin for those who are insulin-dependent. The culture of blame surrounding overweight and obesity causes patients to perceive their illness as being self-inflicted through laziness and low self-control, and other such character judgements rife in Western culture (Thomas et al., 2008). Patients also fear unwanted attention or being mistaken for illicit drug users when publically using vials and syringes (in those who do not use insulin pumps and pens). Schabert et al. noted such stigmatisation can preclude optimal diabetes-related self-management. The negative emotional states induced by stigma causes concealment attempts such as avoiding injecting insulin in public spaces, therefore delaying or foregoing insulin intake (Shiu et al., 2003). Another example of concealment includes reluctance to decline foods with higher caloric values due to embarrassment (Wellard et al., 2008).

Therefore, equipping patients with the necessary coping and self-care techniques may be an important step in managing diabetes-related distress and other associated psychological symptoms. Subsequently, managing psychological barriers may facilitate improved health behaviour geared towards ameliorating diabetes symptoms. Various mind–body approaches exist that could be beneficial to people with diabetes. Mindfulness is an approach that has surged in popularity in many applications, settings and populations (Baer, 2003; Niazi and Niazi, 2011).

Mindfulness as a therapeutic intervention was developed by Dr Jon Kabat-Zinn in 1979 (Kabat-Zinn, 1990). Mindfulness therapies are derived and adapted from Buddhist practices but are delivered secularly. They incorporate breathing techniques and meditation exercises, and aim to channel attention non-judgementally into the present moment. Thus, internal (e.g. emotions, thoughts or sensations) and external (e.g. visual and audible) stimuli are attended to without gauging whether they are important or unimportant, good or bad, pleasant or unpleasant, or correct or incorrect.

Initially, Mindfulness was aimed at managing and reducing stress, particularly for psychological issues such as anxiety, stress-related disorders and depression; hence its alternative nomenclature: Mindfulness-based stress reduction (MBSR). A more recent variant of Mindfulness-based therapy, known as Mindfulness-based cognitive therapy (MBCT), has been developed and initially applied to people suffering from relapses of depression (Segal et al., 2002). As the name suggests, it is a synthesis of MBSR and cognitive behaviour therapy. These Mindfulness-based interventions (MBIs) typically entail participating in weekly 1- to 2-hour long sessions for a period of 8 weeks. The sessions involve guided practice of the aforementioned techniques and exercises.

MBIs have garnered success and acceptance in mental health applications (Chiesa and Serretti, 2011; Khoury et al., 2013). In the decades since its inception, Mindfulness application has increasingly been extended with relative success to physical health conditions including irritable bowel syndrome, chronic pain, diagnoses of cancer and human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) (Niazi and Niazi, 2011; Page, 2012; Simpson and Mapel, 2011). Collectively, this research demonstrates that MBIs can lead to ameliorated medical symptoms by reducing ill-being (e.g. stress, anxiety and depression) and enhancing quality of life and wellness.

Whitebird et al.’s (2009) review considered the potential applicability and efficacy of MBIs for diabetes (in light of the then lack of MBI research on diabetes) by accounting for MBI success when applied to other chronic conditions. Whitebird et al. contended that developing non-judgemental awareness may reduce the burden of diabetes in a similar manner observed in other illnesses. MBIs have since been applied to diabetes, although the research is sparse and unfocused, with varying primary outcomes measured across studies. Encouragingly, evidence shows that MBIs can have psychological benefits when applied to diabetes. Berghmans et al. (2012) found MBIs are effective in reducing stress, anxiety and depression symptoms in patients with type 1 diabetes, and Keyworth et al. (2014) demonstrated Mindfulness yielded improvements in worry and thought suppression in patients with types 1 and 2 diabetes. Sowattanangoon et al. (2008) found a significant association between strength of Buddhist values (of which Mindfulness is integral) and better diabetes self-care and lower HbA_1c. While these were not causal relationships, the extant findings suggest that Mindfulness techniques may be associated with positive health behaviours and improvements in physical health symptoms among people with diabetes. In recent years, MBI studies applied to diabetes have also studied physical health outcome measures while using experimental designs.

Since Whitebird et al.’s (2009) review, more MBI for diabetes research has been conducted. Some of this research has also investigated MBI’s physiological effects. Current literature has not yet aggregated the effectiveness of MBIs on the psychological or physiological complications in diabetes. The purpose of the present systematic review is to follow on from Whitebird et al. (2009) and assess the usefulness of MBIs applied to both types 1 and 2 diabetes. It also highlights gaps in current knowledge pertaining to MBIs for diabetes.

Methodology

PICO statement

To inform and guide study selection and appraisal of articles, the following PICO statement was developed:

In adults with (type 1 or type 2) diabetes, does an adjunctive MBI reduce their diabetes-related physiological (such as HbA_1c level, albuminuria, macrovascular and microvascular) and/or psychological (such as quality of life; diabetes-related stress; depression; stress, anxiety and worry) symptoms?

Inclusion/exclusion criteria

The PICO statement helped to establish the inclusion and exclusion criteria:

Inclusion criteria:

Original primary research studies.

Prospective, quasi-experimental (non-randomised, non-controlled) and randomised controlled trial (RCT) designs.

Adults (aged 18 years or older) diagnosed with type 1 or type 2 diabetes.

MBIs inclusive of MBSR, MBCT or Mindful eating programmes, or dual therapy interventions which include Mindfulness as a major component.

Reported outcomes of glycaemic control, microvascular complications, macrovascular complications, or psychological symptoms.

Exclusion criteria:

Review articles and any other secondary articles, case studies, or qualitative studies.

Symposium or conference articles (as these do not have fully described methodological procedures).

Patients with non-diabetes metabolic conditions.

Patients with gestational diabetes.

Absence of pre- and post-intervention comparison.

Inclusion of uncontrolled physical activity or dietary changes as part of the intervention.

Yoga-focused interventions (these are first and foremost physical activity interventions with Mindfulness integrated rather than the converse. Thus, it is difficult to disentangle and ascertain the sole Mindfulness effects from the physical activity effects as alluded to by Abbott et al. (2014)).

Articles outlining a methodology for an on-going study but had not yet collected or reported results.

Full texts published in languages other than English or French (based on literacy levels of the author team).

Search strategy

A systematic literature review search strategy was devised in consultation with a medical librarian at the university. Five databases were searched as these were deemed the most relevant for Health Psychological research: Medline, Web of Science, PubMed, PsychInfo and Google Scholar. Keywords and Medical subject headings (MeSH) were used as part of the search strategy. For Medline and PsychInfo (1946 to week 4 of May 2015), the search strategy began by searching Mindfulness, expanding this MeSH heading to also search for related subheadings. The search for the MeSH heading Diabetes was also expanded for associated subheadings. These two search results were then combined using the ‘And’ operator. The search strategy was limited to these three basic steps as Mindfulness for diabetes literature is still relatively novel and thus sparse. For the other databases, key terms used were Mindfulness, Mindful* or meditation in combination with diabetes, gly?emi*, neuropathy, retinopathy, nephropathy, macrovascular or vascular. The reference lists of retrieved (primary and secondary) articles were also hand-searched to find any studies not yielded by database searches. Grey literature was not considered. Articles were identified for further review by screening search results’ titles and abstracts. In the event that a study’s design was unclear when reviewing the abstract, the full article was obtained for a full text review. For an illustration of this study identification process, see Figure 1. Titles, abstracts and full texts using the inclusion and exclusion criteria were screened by F.N. and an independent researcher. Any disagreements were reconciled through discussion. If a discrepancy could not be resolved, a third reviewer (J.L.T.) was consulted.

Figure 1.

Flow chart demonstrating identification process of selected MBIs for diabetes articles.

Critical appraisal of included literature

The studies were then critically appraised to assess the risk of bias using the Joanna Briggs Institute (JBI) checklist for experimental studies (see Appendix 1). Upon completing the checklist for each study, judgements about the degree with which quality affects confidence in each study were made. This was also assessed independently by two reviewers (F.N. and an independent researcher).

Data collection

Study characteristics such as the research design, population, setting, intervention details, outcome measures, results observed and risk of bias were collected using a standardised data extraction form (see Appendix 2). The two aforementioned reviewers extracted data independently and discussed any discrepancies to arrive at consensus.

Analysis approach

A narrative synthesis was used for the analysis approach because of the lack of consistency and high variation in measured outcomes across the included studies. This is also the reason as to why a meta-analysis could not be conducted, as no consistent outcome was measured across all the studies.

Results

Electronic searches yielded 264 results. After title and abstract screening, 26 remained for full text review. A total of 11 studies from 15 articles were included in the final review (see Table 1 for a summary of included studies). Reasons for exclusion at full text review stage are listed in Figure 1.

Table 1.

Summary of included articles.

Article, country	Study design and comparator	Participants	Diabetes type	Intervention	Length of intervention	Outcomes
Berghmans (2012), France	RCT	17 adults (3 men, 14 women)Age range = 20–50 years	Type 1 (>10 years)	MBSR (group-based). Weekly 2½-hour sessions	8 weeks	Primary: Stress, anxiety and depression
Dreger et al. (2013), Canada	Quasi-experimental	11 Aboriginal adults(1 man, 10 women)Mean age ± SD = 60.1 ± 8.7 years	Type 2	MBSR (group-based, adapted culturally and for diabetes). Weekly 2-hour sessions. Plus mindfulness home practice: 20–30 minutes, 5 days a week	8 weeks (plus 2-month follow-up)	Primary: HbA1c, blood pressureSecondary: Weight, health-related quality of life, psychological distress, subjective well-being, diabetes self-care, Mindfulness
Gregg et al. (2007), USA	RCT with diabetes education only control	81 adults (43 men, 38 women)Mean age = 50.9 years (SD unreported)	Type 2	Acceptance and commitment therapy (ACT). Group-based and adapted for diabetes	4-hour ACT (including acceptance and Mindfulness skills) workshop in addition to control group’s diabetes education workshop 7 hours) (3-month follow-up)	Primary: HbA1cSecondary: Self-management, Changes in ACT processes
Hartmann et al. (2012), Germany	RCT with treatment as usual control	110 adults (86 men, 24 women)Age range = 30–70 years	Type 2 (>3 years) with albuminuria	The HEIDIS study: MBSR (group-based and adapted for diabetes) once a week, plus a booster session at 6 months	8 weeks (plus 1-year follow-up)	Primary: AlbuminuriaSecondary: Systolic and diastolic blood pressures, HbA1c depression, stress, health status
Keyworth et al. (2014), UK	Sequential Mixed methods Pre-test, post-test experimental design	40 adults (19 men, 21 women) with age range of 54–85 years	Type 2; coronary heart disease; patients with both Type 2 and heart disease	Pilot study. MBSR variant (group-based and adapted for diabetes). Weekly 2-hour sessions (first session lasted 2½ hours)	6 weeks	Primary: Worry, thought suppressionSecondary: Intervention feasibility and acceptability
Kopf et al. (2014), Germany (same study (HEIDIS) as Hartmann (2012))	RCT with treatment as usual control	110 adults (86 men, 24 women)Age range = 30–70 years	Type 2 (>3 years) with albuminuria	The HEIDIS study: MBSR (group-based and adapted for diabetes) once a week, plus a booster session at 6 months	8 weeks (plus 1-, 2- and 3-year follow-up)	Primary: AlbuminuriaSecondary: Metabolic parameters (HbA1c), intima media thickness, depression, stress, health status and cardiovascular events
Miller et al. (2012) and Miller et al. (2014), USA	RCT with Diabetes Self-Management Intervention	52 adults (19 men, 33 women)Age range = 35–65 years	Type 2 (>1 year)	Mindful Eating Intervention: 8 weekly and 2 biweekly 2½-hour group-based sessions	8 weeks (plus 1- and 3-month follow-up)	Primary: Dietary intake, body weight, HbA1c, fasting plasma glucose, fasting insulin, depressive symptoms, nutrition and eating-related self-efficacySecondary: physical activity, outcome expectations, cognitive control, disinhibition of control regarding eating
Rosenzweig et al. (2007), USA	Prospective observational study	14 adults (5 men and 9 women)Age range = 30–75 years	Type 2 (>1 year)	MBSR. 150-minute group-based session once a week plus 7-hour weekend session	8 weeks (plus 1-month follow-up)	Primary: HbA1c, blood pressure, body weight, symptom checklist–90 revised (anxiety, depression, somatisation, general psychological distress scores)
Schroevers et al. (2013), The Netherlands	RCT with waitlist-control group	24 adults (14 men, 10 women)Age range = 44–65 years	Type 1 or 2	Individual MBCT (I-MBCT). 8 weekly individual sessions of 1 hour	8 weeks (plus 3-month follow-up)	Primary: Depressive symptoms and diabetes-related distressSecondary: Mindfulness, Awareness and attention regulation
Teixeira et al. (2010), USA	Pre-test, post-test experimental design	20 adults (5 men, 15 women)Age range = 50–92 years	Type 2 (>1 year)	Pilot study. Mindfulness meditation (not MBSR)	4 weeks	Primary: Neuropathic Pain, Quality of Life and Sleep quality
Tovote et al. (2014) and Tovote et al. (2015), The Netherlands	RCT with CBT group	94 adults (48 men, 46 women)Age range = 36–65 years	Types 1 and 2 (with symptoms of depression)	MBCT. Weekly (individual) 1-hour sessions plus daily home practice for 30 minutes/day	8 weeks (plus 9-month follow-up)	Primary: Severity of depressive symptoms, DepressionSecondary: Anxiety, well-being, diabetes-related distress, and HbA1c
Van Son et al. (2013) and Van Son et al. (2014), The Netherlands	RCT with waitlist-control group	139 adults (70 men, 69 women)Mean age ± SD = 56.5 ± 13 years	Types 1 and 2 (with low emotional well-being)	The DiaMind study: MBCT (group-based and adapted for diabetes) 2 hours a week and home practice for 30 minutes/day	8 weeks	Primary: stress, anxiety and depression, mood, diabetes distressSecondary: Quality of Life, HbA1c

RCT: randomised controlled trial; MBSR: Mindfulness-based stress reduction; HEIDIS: Heidelberger Diabetes and Stress; MBCT: Mindfulness-based cognitive therapy; SD: standard deviation; CBT: cognitive behavioural therapy.

Study characteristics

Included articles dated from 2007 onwards. Studies were conducted in the United States (n = 4), the Netherlands (n = 3), Germany (n = 1), France (n = 1), United Kingdom (n = 1) and Canada (n = 1). Most studies focused on participants with type 2 diabetes; only Berghmans et al. (2012) focused on participants with type 1 diabetes. Three studies included participants with both types. One study included patients with diabetes and/or coronary heart disease. The majority of participants across trials were Caucasian, however the sample in Dreger et al. (2013) consisted of Canadian Aboriginals. Women represented the larger proportion of participants in all but three studies. There was a wide age range of participants, from 18 to 92 years old across studies.

Intervention characteristics and measured outcomes

There was much heterogeneity in results regarding intervention types, duration and measured outcomes. Six were MBSR trials, two used MBCT trials. One was a Mindful eating trial (Miller et al., 2012, 2014), another trial was a dual therapy trial (Gregg et al., 2007), and a final trial (Teixeira, 2010) was described as a form of Mindfulness meditation based upon, but not specifically, MBSR. Most trials were 8 weeks long (n = 9). Outcomes included various physiological (HbA_1c, blood pressure, weight, albuminuria and neuropathic pain), psychological (stress, anxiety, depression, distress, quality of life, diabetes self-care, health status, worry, thought suppression, sleep quality, mood, subjective well-being mindfulness) and dietary measures (nutrition and eating-related self-efficacy, disinhibition of control regarding eating). Eight were delivered to groups, two delivered to individuals and one provided a Mindfulness CD for home practice.

Effect of MBIs on physical health outcome measures

Physical health outcomes included weight (n = 4), HbA_1c (n = 7), diabetic neuropathy (n = 1), albuminuria (n = 1) and blood pressure (n = 3). Few studies reported weight outcomes. One trial reported weight-loss (Miller et al., 2012); however, three trials reported no change in weight (Dreger et al., 2013; Kopf et al., 2014; Rosenzweig et al., 2007). Four interventions successfully lowered HbA_1c levels. These studies were either tailored for diabetes patients, towards eating behaviour or culturally adapted. However, the three largest studies found no change in HbA_1c. Teixeira (2010) reported no effect of MBI on diabetic neuropathy. One of the larger trials, the Heidelberger Diabetes and Stress (HEIDIS) study reported no post-intervention effect on albuminuria (reported in Hartmann et al., 2012). At 1-year follow-up, albuminuria improved: there was a reduction in urinary albumin–creatinine ratio (ACR). However, this was not sustained after 2- and 3-year follow-up (reported in Kopf et al., 2014). Blood pressure reduction was observed in the two smallest studies. Diastolic (but not systolic) blood pressure reduction was observed in the HEIDIS study, however these effects were lost at 2- and 3-year follow-up.

Effect of MBIs on psychological outcome measures

Studied psychological outcomes were as follows: anxiety (n = 5), stress (n = 3), depression (n = 6), diabetes-related distress (n = 3), distress (n = 3), quality of life (n = 2), well-being (n = 1), health status (n = 1), illness condition acceptance (n = 2), self-management (n = 1), coping (n = 1), sleep and relaxation (n = 1), worry (n = 1), thought suppression (n = 1) and Mindfulness (n = 2). It is important to note the subtle distinctions between stress, anxiety and distress. Stress is a response to a known stressor that elicits activation of the sympathetic nervous system (Ahmed et al., 2011). Anxiety has similar symptoms to stress but no identifiable cause. Anxiety is characterised by a state of panic and feeling of helplessness (American Psychiatric Association (APA), 2013). Distress is generally regarded as a broad umbrella term encompassing various negative states and has its own measuring scales (Ridner, 2004). In all five studies that took measures of anxiety, anxiety symptoms were reduced. Stress reduction was observed in two trials and in the HEIDIS study (Hartmann et al., 2012) via per-protocol analysis (a comparison of experimental groups which only includes participants who completed the intervention). However, in the HEIDIS study, after an intention-to-treat analysis (a comparison of experimental groups which includes all participants as originally allocated following randomisation), no stress reductive effect was observed. Furthermore, the HEIDIS stress reduction effects were not sustained at follow-up of 2 and 3 years. Depression symptoms were reduced in six studies including the three largest studies, of which Van Son et al. (2013) observed clinically significant effects. Tovote et al. (2015) found sustained effects on depression symptoms at 9-month follow-up. Conversely, when Van Son et al. (2013) followed up after 6 months, depressive symptom reductions measured by an alternate scale (Profile of Mood States (POMS; Curran et al., 1995)) were not significant compared to baseline.

Four interventions led to reductions in distress measures. Conversely, Van Son et al. (2013) and Dreger et al. (2013) found no change in distress measures. Five interventions found improvements in measures related to wellness (quality of life, well-being and health status). Two trials led to greater illness condition acceptance. However, one of these MBIs also included components of Acceptance and commitment therapy. One study, Gregg et al. (2007), assessed behavioural adaptation and reported enhanced self-management. Keyworth et al. (2014) observed improvements in sleep (qualitatively reported), relaxation (qualitatively reported), worry and thought suppression. Finally, two studies assessed Mindfulness scores. Schroevers et al. (2013) observed an increase in one of the two Mindfulness subscale values: act with awareness (but not accept without judgement). Dreger et al. (2013) found no significant change in Mindfulness scores post-intervention.

Dietary outcome measures

Miller et al. (2012) reported reductions in energy intake and glycaemic load. Dreger et al. (2013) found small to medium effects for general diet improvement and high-fat food avoidance, although these changes were not statistically significant.

Factors potentially related to intervention effectiveness

Intervention characteristics can affect effectiveness and thus need to be examined when assessing intervention effectiveness. Intervention duration varied across studies. Three studies did not follow the 8-week MBI template: Gregg et al. (2007) opted for a 1-day, 4-hour workshop; Teixeira (2010) delivered a 4-week MBI programme; and Keyworth et al. (2014) delivered a 6-week programme. Interestingly, the more brief intervention durations were as likely to result in positive outcomes. Gregg et al. (2007) observed HbA_1c level reductions with the 1-day workshop, suggesting that 8 weeks were not required to see beneficial outcomes. However, this group delivered a dual therapy with Acceptance and commitment therapy components, which could have contributed to these beneficial effects in a shorter time span. Teixeira (2010) and Keyworth et al. (2014) measured outcomes that other studies did not, making it impossible to compare across studies.

Additional factors that may have affected intervention effectiveness include experience and training level of the practitioner, and the use of a group- or individual-delivery format approach. Five studies gave information regarding their practitioner’s years of experience and/or clinical background. The experience and training level of the practitioner did not have an influence on outcomes. Nine studies used a group-based delivery format, with the remaining three individual-based. Mode of delivery did not appear to influence outcomes. A final factor that may affect MBI effectiveness was whether the MBIs were adapted for their population. Five studies were adapted to be more diabetes-focused. Of these five, Dreger et al. (2013) was also adapted to incorporate cultural (Canadian Aboriginal) healing traditions. Additionally, Miller et al. (2012) adapted their intervention to focus on eating and hunger cues as their aim was to reduce weight control issues common among people with diabetes.

Acceptability and feasibility

Where reported within studies, MBIs were deemed acceptable and feasible. Teixeira (2010) noted a low attrition rate and reported that the intervention was well received and feasible. Dreger et al. (2013), Gregg et al. (2007) and Schroevers et al. (2013) reported that participants stated they were satisfied with the intervention. Dreger et al. (2013) in particular noted that their culturally adapted MBI was feasible for the target minority group under study.

Study quality (risk of bias)

The risk of bias for each study is summarised in Table 2. Overall, the general quality of studies was mixed, ranging from 2 to 10 and scoring an average of 6.3 (out of a maximum score of 11) on the JBI critical appraisal checklist. The seven RCTs however were generally of high quality, scoring an average of 9. The non-RCTs scored an average of 3.6. Not all studies used two comparable groups, with five using different quasi-experimental designs. This causes concern for their internal validity and casts doubt over how readily we can establish the causality of these MBIs’ beneficial effects. It must be noted, however, that controlled trials yielded similar beneficial effects, particularly for psychological outcomes. Six of the 7 studies that used randomised designs specified their randomisation method; most that did report randomisation method used computer generated number sequences. Only 1 study confirmed blinding participants, with the other 11 neglecting to report any information about this methodological aspect. This increases the risk of bias as participants are aware of their group allocation. The majority of studies had complete outcome measure data (for all participants) and also used intention-to-treat analyses (with listed explanations for any dropout during the intervention). Six studies conducted follow-up. Of these, two had not retained an adequate sample size of 80 per cent at follow-up (in accordance with the JBI critical appraisal tool). Another study also suffered potential attrition bias with a dropout rate of approximately 25 per cent from their experimental group. The studies generally measured outcomes reliably.

Table 2.

Summary of quality of included literature.

Source	Was the assignment to treatment groups random?	Were participants blinded to treatment allocation?	Was allocation to treatment groups concealed from the allocator?	Were the outcomes of people who withdrew described and included in the analysis?	Were those assessing outcomes blind to the treatment allocation?	Were the control and treatment groups comparable at entry?	Were groups treated identically other than for the named interventions?	Were outcomes measured in the same way for all groups?	Were outcomes measured in a reliable way?	Was there adequate follow-up (>80%)?	Was appropriate statistical analysis used?
Berghmans et al. (2012), France	Yes	Unclear	Unclear	Yes	Yes	Yes	Yes	Yes	Yes	No (no follow-up)	Yes
Dreger et al. (2013), Canada	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	Yes	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	Yes	Yes	Yes
Gregg et al. (2007), UK	Yes	Unclear	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Hartmann et al. (2012), Germany	Yes	Unclear	Unclear	Yes	Unclear	Yes	Yes	Yes	Yes	Yes	Yes
Keyworth et al. (2014), UK	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	Unclear	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	Yes	No (no follow-up)	Yes
Kopf et al. (2014) Germany (same study (HEIDIS) as Hartmann, 2012)	Yes	No	Unclear	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Miller et al. (2012) and Miller et al. (2014), USA	Yes	Unclear	Yes	No	Yes	Yes	Yes	Yes	Yes	No	Yes
Rosenzweig et al. (2007), USA	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	Unclear	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	No (no other treatment groups)	Yes	No	Yes
Schroevers et al. (2013), The Netherlands	Yes	Unclear	Unclear	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Teixeira et al. (2010), USA	Yes	Unclear	Yes	No	Yes	Yes	Yes	Yes	Yes	No (no follow-up)	Yes
Tovote et al. (2014) and Tovote et al. (2015), USA	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No (no follow-up)	Yes
Van Son et al. (2013, 2014), The Netherlands	Yes	Unclear	Yes	Yes	Yes	Yes	Yes	Yes	Yes	No (no follow-up)	Yes

HEIDIS: Heidelberger Diabetes and Stress.

Discussion

The aim of this review was to follow on from Whitebird et al.’s (2009) review in aggregating and assessing the usefulness of MBIs applied to both types 1 and 2 diabetes. It also aimed to highlight gaps in current knowledge concerning MBIs for diabetes. A total of 11 studies (from 15 articles) met the inclusion criteria. Congruent with prior literature (Chiesa and Serretti, 2011; Khoury et al., 2013), there was relatively consistent evidence for MBIs’ effectiveness on psychological outcomes. Results found mixed evidence for MBIs’ effectiveness on physiological outcomes.

MBIs had mixed evidence for effectiveness in alleviating physical health symptoms – again similar to MBIs for other chronic illnesses (Carlson, 2012; Niazi and Niazi, 2011). Although four studies found that MBIs reduced HbA_1c levels, another three studies (which were larger, higher quality with lower risk of bias) found no change. Blood pressure reduction was observed in three studies; however, these effects were lost at 2- and 3-year follow-up in largest of these. The HEIDIS study found no initial post-intervention effect on albuminuria; nevertheless, at 1-year follow-up reductions in urinary ACR were observed. However, these effects were not sustained when measured at 2- and 3-year follow-up. Although Teixeira (2010) found no MBI effect on diabetic neuropathy, these results are difficult to directly compare to the other published studies due to Teixeira et al.’s method of Mindfulness delivery being via CD and not via face-to-face delivery by a Mindfulness practitioner. Regarding the impact of MBIs on weight-loss, only Miller et al. (2012) (of four studies to measure weight change) reported (moderate) weight-loss. Notably, Miller et al. (2012) implemented a Mindful eating-focused MBI; thus, it appears MBIs could have at least moderate effects on weight-loss when focusing on Mindful eating. Evidently, the small sample size and diverse delivery methods within the published studies make it difficult to conclude the extent to which MBIs are effective in improving physiological outcomes in people with diabetes. These results are reminiscent of Katterman et al.’s (2014) MBIs for obesity systematic review where MBIs had mixed effects on weight-loss but reduced binge eating and emotional eating.

The findings were consistently more positive with regard to psychological outcomes. MBIs elicited improvements in stress, anxiety and depression symptoms similar to MBIs for other chronic illnesses (Bohlmeijer et al., 2011; Lawrence et al., 2013; Niazi and Niazi, 2011). Four of six studies observed improvements in distress. Among other main psychological findings, four studies found improvements in quality of life, well-being or health status. Keyworth et al. (2014) observed improvements in worry and thought suppression. According to the formulation model applied by Whitebird et al. (2009) and Dreger et al. (2013), such psychological and psychosocial benefits may enable subsequent positive health behaviour change as this mind–body model suggests that reducing stress and other psychological issues may facilitate subsequent physical health improvements.

There are various factors that may influence MBI effectiveness and provide some insights into the currently limited evidence for physical health benefits. As MBIs for diabetes research is in its infancy, much of the research is exploratory. With little consistency in methods and measured outcomes, it remains too early to attempt to establish any theoretical underpinning. Inevitably, without a theoretically driven approach this could potentially diminish the effectiveness of MBIs for diabetes. This is a recognised weakness of the current evidence base, and future studies should be theoretically informed, and designed and evaluated to allow for an examination of the theoretical rationale for why MBIs may have value for diabetes management.

Another factor influencing the effectiveness of MBIs is their duration. Although it is possible to detect physiological changes such as HbA_1c, weight-loss and blood pressure in a period of 8 weeks (the typical MBI duration), this period of time may be insufficient to gain adequate mastery over Mindfulness practice and subsequently elicit physiological benefits. Therefore, longer-term follow-up periods may be necessary to gauge the effectiveness of Mindfulness practices on physical health outcomes (as also noted by Abbott et al., 2014 in relation to MBIs for vascular disease). This is pertinent when it is considered that Hartmann et al. (2012) observed positive effects for albuminuria, intramedia thickness and depression after 1 year but not immediately at post-intervention. They attributed this observation to the temporal accumulation of MBI effects.

In contrast, among the studies that conducted follow-up assessments, several beneficial effects (blood pressure, albuminuria and depression in Van Son et al. (2013)) were not maintained. Arguably, this raises questions about MBIs’ long-term usefulness for diabetes populations. However, it is difficult to draw any firm conclusions about this issue, as authors did not report whether participants continued to practice (and possibly master) Mindfulness after the intervention. Consequently, the loss of MBIs’ effects may result from participants ceasing Mindfulness practice, reflecting the possible lack of long-term acceptability and sustainability of Mindfulness as opposed to its efficacy. MBIs, as with any behavioural intervention, require regular practice to be effective. It is worthwhile to note that the issues of long-term acceptability, adherence and sustainability are not exclusive to MBIs, as these issues are also present in other behavioural interventions such as physical activity and dietary programmes, as well as medical treatments (McAuley et al., 2003; Osterberg and Blaschke, 2005; Wadden et al., 2004). Thus, the implications for future research are that it is not only important to record Mindfulness measures pre-intervention, immediately post-intervention, and at longer-term follow-up, it is also integral to the treatment’s evaluation to assess and report if participants continue to incorporate regular Mindfulness methods into their lives following completion of the intervention. It would also be beneficial to assess whether on-going support is needed to facilitate maintenance of MBI practice, and if so, what form of support would be most effective in promoting the sustainability of one’s practice. There is the possibility that people with diabetes are reluctant to invest more time and effort on Mindfulness practice in addition to the already considerable diabetes self-care they undertake. It is suggested that future research explore this supposition to determine if it is correct.

The type of MBI may also be a possible determinant of effectiveness. Miller et al.’s (2012) Mindful eating intervention, which aimed to develop a personal understanding of nutritional and diabetes needs and Mindful awareness pertaining to eating, was effective in resulting in several physical and psychological benefits. Thus, it is possible that an MBI focusing on specific health behaviours (such as eating) may be more successful. Eight studies used MBSR interventions, whereas two used MBCT. It was not possible to compare the two major subtypes of MBI: MBSR and MBCT. This was because the MBCT studies focused on outcome measures not observed in the other studies. As aforementioned, Gregg et al. (2007) used a dual therapy intervention. Similar to one MBSR intervention and Miller’s Mindful eating intervention, they observed HbA_1c reductions. It can also be noted that of the three studies to find no change in HbA_1c, two used MBSR and one used MBCT. From this limited number of studies, it appears that the specific type of MBI may not play a role in the MBIs’ effectiveness on HbA_1c. Teixeira (2010) used an unidentified MBI and observed outcomes not examined in other studies (apart from quality of life), which precludes outcome comparisons to other studies. Teixeira’s study was successful in improving quality of life similar to Van Son et al.’s (2013) MBSR study. Broadly speaking, there was too much heterogeneity across outcomes and too few non-MBSR studies to make comparisons of effectiveness for type of MBI.

Practitioner experience is another potentially relevant factor. Only 5 (of 11) MBI studies declared the level of Mindfulness training and/or experience of personnel delivering the MBIs. As such, it was difficult to compare studies delivered by trained and experienced practitioners against untrained and/or inexperienced practitioners. As mentioned earlier, Teixeira’s (2010) CD-based intervention did not elicit physiological benefits. From the information provided in the studies included in this review, there was no clearly discernible pattern between practitioner and MBI physical outcome effectiveness. Studies that reported positive physical outcomes were among those that did not detail practitioner experience (Gregg et al., 2007; Hartmann et al., 2012; Rosenzweig et al., 2007). Interestingly, the 5 studies confirming that practitioners had relevant Mindfulness experience all reported significant psychological benefits.

Mode of delivery, such as whether the MBIs were group-based or individual-based, could affect MBI effectiveness. Generally, from the included articles, there does not appear to be a pattern to suggest either group-based or individual-based MBIs are more effective than the other. This is inconsistent with past findings from another MBI application – MBIs for weight-loss literature. In this application, group-based delivery was more successful as it elicited greater weight-loss and reduced cognitive-behavioural avoidance (Mantzios and Giannou, 2014). However, Mantzios and Giannou (2014) found that individual practice did hold some advantages for the psychological outcomes of Mindfulness and a decrease in (eating-related) impulsivity.

Some MBIs were adapted for a diabetes population. Dreger et al.’s (2013) MBI was adapted for a Canadian Aboriginal culture as well as a diabetes population. They found physical and psychological benefits. Although a small study, findings support the need for more research examining the impact of tailored MBIs for ethnically diverse groups, of which many are at higher risk for type 2 diabetes (Hippisley-Cox et al., 2009). Four studies also tailored their MBIs specifically for a diabetes population. Hartmann et al. (2012) found albuminuria improvements after 1 year; however, this was the only study to observe albuminuria. As such, it cannot be stated if a non-adapted MBI would result in positive changes for this outcome. For psychological outcomes (such as depression, anxiety, stress, distress and quality of life), there were diabetes-specific and non-specific MBIs that resulted in improvements. Therefore, this suggests that MBIs do not need to be specific for diabetes to influence psychological outcomes. Overall, there was no discernible pattern between tailoring and outcomes.

There were some limitations in terms of the quality of the studies included in this review. Seven of the 11 included studies were RCTs. These studies were generally well conducted and of high quality, scoring an average of 9 (out of 11) on the JBI critical appraisal tool. Therefore, they had a lower risk of bias. Six of these studies did not satisfy the criterion that participants were blinded to treatment allocation. However, as noted by Abbott et al. (2014), it is impossible to blind participants from their treatment allocation in MBI research. The 5 non-RCT studies were mainly observational studies, with the exception of Dreger et al. (2013), employing a quasi-experimental design. These 5 studies scored an average of 3.6 on the JBI critical appraisal tool, indicating a higher risk of bias. However, of these, Dreger et al. and Teixeira (2010) satisfied quality checklist criteria that were applicable to them. Furthermore, as Anglemyer et al. (2014) suggest, a non-RCT study is not inherently a poor quality study; it only highlights a risk of bias and that other methodological considerations have more governance in a study’s quality. Therefore, these studies should not be discredited, as they can be informative of some of MBIs’ potential effectiveness, especially when it is considered that results herein are congruent with MBI effects for other physical health research (Bohlmeijer et al., 2011; Niazi and Niazi, 2011).

Another limitation of the existing literature focusing on MBIs for diabetes is that the studies focus on disparate aspects of diabetes, with a lack of consistency and high variation in measured outcomes across studies. To better understand MBIs’ effects on diabetes, there is a need for more consistency in outcome measures, which is recognised as a growing problem in clinical trials literature (Kirkham et al., 2010). The Core Outcome Measures in Effectiveness Trials (COMET) initiative aims to unite relevant stakeholders in agreeing upon a set of outcome measures for given treatments to facilitate the suitable collation, comparison and aggregation of studies (Williamson et al., 2012). This was initially applied to rheumatoid arthritis (Smolen et al., 2010), before being applied to other medical conditions. Outcome sets entail the minimum, pertinent outcomes that should be assessed and reported in all future interventions of a given condition.

Therefore, a standardised core outcome set could be used by all forthcoming research in the field of mindfulness and diabetes. Physiological outcomes such as HbA_1c and weight are recommended. Psychological outcomes such as stress, anxiety and depression, quality of life and a measure of Mindfulness are recommended for inclusion. In this review, only two articles were identified that reported Mindfulness values as an outcome measure. As such, we are not able to determine how effective participants were at utilising learned techniques and exercises post-intervention across the included studies.

The present review is not without limitations. First, the included non-RCTs were of relatively low quality, scoring an average of 3.6 (out of 11) on the JBI critical appraisal checklist. Therefore, these studies have a higher risk of bias and are more prone to spurious findings. However, an executive decision was made to include such articles due to the novelty and scarcity of MBIs applied to diabetes to help illuminate knowledge pertaining to this particular application. Similarly, included studies were heterogeneous in terms of outcome measures, settings, delivery mode, demographics and MBI type. Such aspects made the scope of this review broad and only allow for a relatively superficial understanding of MBIs’ effect on diabetes. Additionally, the inclusion criteria were limited to studies published in English and French (due to the linguistic abilities of the authors). As such, non-English language studies were omitted and could have influenced the results.

The outcomes of this review highlight research implications moving forward. For future studies, it is recommended that a standardised core outcome set is identified and applied. It would also be good practice for future research to assess and report whether participants incorporate Mindfulness practice into their lives after the intervention, particularly when reporting follow-up outcomes. The potential mechanisms as to how Mindfulness may confer positive effects in managing some chronic diseases (including diabetes) remain unclear. Literature has postulated vague potential formulation models for MBIs, where psychological and psychosocial factors may impede positive health behaviour (Lawrence et al., 2013; Whitebird et al., 2009). Nonetheless, the literature herein is not able to explain why MBIs may be effective in managing diabetes. Thus, more mechanistic research is required before the effective components of Mindfulness can be established.

In conclusion, while research focusing on the benefits of MBIs in people with diabetes (and other chronic illnesses) is new and relatively limited, the studies included in this systematic review indicate some promise, particularly for psychological outcomes. Much of the current literature remains unfocused with disparate outcome measures. Further research addressing the limitations described here is required to elucidate the potential benefits of MBIs for diabetes.

Footnotes

Appendix 2

Standardised data extraction form

Systematic review data extraction sheet:

Authors:

Year:

Journal:

Study Method:

Study design (RCT, quasi-experimental or prospective cohort):

Type of mindfulness-based intervention (e.g. MBCT, MBSR, Mindful eating or other):

Sample ethnicity:

Setting:

Groups (N):

Group A: (N=)

Group B: (N=)

Group C: (N=)

Findings and conclusions:

Change in (measured) physiological outcomes:

HbA_1c level:

Albuminuria level:

Blood pressure:

Weight:

Other:

Change in (measured) psychological outcomes:

Distress:

Diabetes specific/related distress:

Depression:

Anxiety:

Stress:

Quality of Life:

Other:

Appendix 1

JBI critical appraisal checklist for experimental studies

JBI Critical Appraisal Checklist for Experimental Studies
Reviewer__________________________Date________________ Author____________Year______________Record number_____________
	Yes	No	Unclear
1. Was the assignment to treatment groups random? 2. Were participants blinded to treatment allocation? 3. Was allocation to treatment groups concealed from the allocator? 4. Were the outcomes of people who withdrew described and included in the analysis? 5. Were those assessing outcomes blind to the treatment allocation? 6. Were the control and treatment groups comparable at entry? 7. Were groups treated identically other than for the named interventions? 8. Were outcomes measured in the same way for all groups? 9. Were outcomes measured in a reliable way? 10. Was there adequate follow-up (>80%) 11. Was appropriate statistical analysis used?
Overall appraisal: Include □ Exclude □ Seek further info. □
Comments (Including reasons for exclusion) __________________________________________________________________________________________________________________________________________________________________

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship and/or publication of this article.

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