Overview of included studies.
Electronic database searches produced 10,630 articles with 2,075 remaining after the removal of duplicates. After screening the title and abstract of each, the full text of 91 articles was retrieved for further review. A total of 30 articles reporting findings from k [number of studies] =26 distinct intervention trials were selected for final inclusion, all of which were hand-searched for additional studies. A full breakdown of this search process including reasons for exclusion can be seen in Figure 1. Numerous studies (k=11) examined more than one risk factor. Of the included studies, the majority examined outcomes related to diet (k=13), obesity (k=9), and smoking (k=11). The remaining studies examined outcomes related to exercise (k=4), diabetes (k=3), and blood lipids (k=2). Number of participants ranged from 18-412 with k=20 studies having n<100 participants. All articles included were published between 2011-2020. Six articles that met inclusion criteria were part of the same two parent studies [65-70] and present the same basic implementation characteristics.
Table 2. Overview of Included Studies (k=30 published reports from 26 distinct trials)
Study
|
n
|
Risk factor(s)
|
Participants
|
Intervention*
|
Control(s)*
|
Outcomes measured
|
Primary Findings
|
Arch et al., 2016
|
391
|
Diet
|
Undergraduates (~20 years of age)
|
Brief Mindfulness Instruction
|
Distraction, No Instruction
|
Affect, perception of hunger, calories consumed
|
Evidence supports treatment for reduction of calories consumed.
|
Brewer et al., 2011
|
88
|
Smoking
|
Adult smokers
|
Mindfulness training adapted for smokers
|
FFS
|
Abstinence from smoking
|
Treatment reduced cigarette use, cravings, trends toward increased abstinence.
|
Carmody et al., 2012
|
36
|
Diet
|
Prostate cancer patients
|
Novel
|
Waitlist
|
Prostate-specific antigen, body weight, quality of life, dietary changes, BMI
|
Reductions in prostate-specific antigen correlating with mindfulness and positive eating behaviors.
|
Carpenter et al., 2019
|
75
|
Diet, Obesity
|
Obese adults
|
MYW
|
Weight Talk (WT)
|
Weight, emotional eating
|
Feasibility & acceptability supported. No significant between-group difference in weight loss, but with increased weight loss predicted in treatment group.
|
Chacko et al., 2016
|
18
|
Diet, Obesity
|
Post-bariatric patients
|
Novel
|
TAU
|
Feasibility & acceptability of intervention; changes in weight, eating behaviors, psychosocial outcomes, and metabolic and inflammatory biomarkers
|
Feasibility & acceptability supported. Reduced emotional eating in treatment group at 6 mo but no significant between-group reduction in weight. Sig. increase in HbA1C.
|
Corsica et al., 2014
|
53
|
Diet
|
Overweight adults at risk for obesity
|
Modified MBSR
|
Stress-eating intervention, MBSR
|
Weight, stress-related eating
|
Reduced stress-eating; moderate effect on weight loss in treatment group..
|
Davis et al., 2013
|
55
|
Smoking
|
Smokers with binge-drinking
|
MTS
|
Interactive learning for smokers
|
Smoking abstinence and reduction in alcohol intake
|
Higher prevalence of abstinence in treatment group 2 weeks post-quit.
|
Davis et al., 2014a
|
198
|
Smoking
|
Low-SES smokers
|
MTS
|
TAU
|
6-month smoking abstinence
|
Feasibility & acceptability supported. Significantly higher abstinence rates in treatment-initiators at 4 weeks, 6 months. Significant improvements in emotional regulation.
|
Davis et al., 2014b
|
135
|
Smoking
|
Low-SES smokers
|
MTS
|
FFS Enhanced
|
Smoking abstinence
|
No between-group difference in abstinence found at 4 weeks. Nonsignificant improvement in abstinence at 24 weeks. Reductions in urge intensity correlated to increased mindfulness.
|
Garrison et al., 2018
|
325
|
Smoking
|
Adult smokers
|
Novel app
|
Alternative app
|
Craving, abstinence from smoking
|
No group difference found in abstinence at 6 mo. Nonsignificant reduction in smoking. Reductions in craving observed in treatment group.
|
Gillman & Bryan, 2020
|
78
|
Exercise
|
Adults with insufficient exercise
|
Brief-MP
|
Distraction, associative attentional focus
|
Perceptions, duration and frequency of exercise
|
Higher positive affective response over controls. No difference in minutes of exercise.
|
Ingraham et al., 2017
|
80
|
Diet, Exercise, Obesity, Lipids
|
Adult obese lesbians >40 years old
|
WHAM
|
Delayed start group
|
Mindful eating, fruit & vegetable intake, water consumption, physical activity, Hemoglobin A1c, fasting lipids
|
Statistically significant improvements in cholesterol levels and increased vegetable intake observed in treatment group.
|
Janes et al., 2019
|
33
|
Smoking
|
Adult smokers
|
Novel
|
QuitGuide
|
Decline in smoking predicted by reduced activity in the posterior cingulate
|
Reduction in posterior cingulate activity relative to smoking cues; fewer cigarettes smoked over controls.
|
Lotfalian et al., 2020
|
60
|
Smoking
|
Adult smokers
|
Ujjay breath
|
Coping strategy & no treatment
|
Smoking craving, withdrawal, and negative affect
|
Smoking reduction 24 hours post treatment over controls. Decreased craving over no treatment.
|
Miller et al., 2012
|
52
|
Diabetes, Diet, Exercise
|
Overweight adults with diabetes
|
MB-EAT-D
|
Smart Choices
|
Dietary intake, physical activity, weight, glycemia, and fasting insulin
|
Treatment produced significant decrease in energy intake, reduction in weight, and decrease in glycemic load. No differences between-group in weight change, BMI, waist circumference, fasting glucose, HbA1c, or insulin.
|
Miller et al., 2014
|
52
|
Diabetes, Diet
|
Overweight adults with diabetes
|
MB-EAT-D
|
Diabetes self-management education (DSME)
|
Regulation of food intake, weight
|
Comparable but not superior to control intervention for diabetes self-management.
|
Raja-Khan et al., 2017
|
86
|
Obesity
|
Overweight women
|
MBSR
|
Health education
|
Fasting glucose, weight, A1c and lipid profile, cortisol, psychological stress, mindfulness
|
MBSR showed significant decreases in fasting glucose versus control.
|
Ruscio et al., 2015
|
44
|
Smoking
|
Adult smokers
|
Brief-MP
|
Sham meditation
|
Negative affect, craving, cigarettes smoked
|
Nonsignificant reductions in craving & negative affect and significant reductions in cigarettes smoked over time.
|
Singh et al., 2014
|
51
|
Smoking
|
Smokers with intellectual disabilities
|
Mindfulness training
|
TAU
|
Number of cigarettes smoked
|
Significant reduction in smoking & improved abstinence at 1-year vs control.
|
Smith et al., 2018
|
36
|
Diet, Obesity
|
Overweight menopausal women
|
MEAL
|
Matched active control without meditation
|
Weight, body mass index, waist-hip ratio, binge eating, interleukin-6, C-reactive protein (CRP), psychological measures
|
Reductions in weight loss, BMI, and waist-to-hip ratio in both treatment and control.
|
Spadaro et al., 2018
|
46
|
Diet, Obesity
|
Overweight adults
|
Standard behavioral weight loss program + Mindfulness Meditation
|
Standard behavioral weight loss programs
|
Weight loss, dietary intake, eating behaviors, physical activity, mindfulness
|
Significant group by time interaction found for weight loss favoring treatment over control. Eating behaviors and dietary restraint improved significantly in treatment compared with controls.
|
Tang et al., 2013
|
60
|
Smoking
|
Healthy students, half smokers
|
IMBT
|
Relaxation Training
|
Smoking reductions, nicotine dependence self-report (FTND), number of cigarettes smoked, brain measures relating to smoking reductions/self control measuring fractional amplitude of low-frequency fluctuation (fALFF) with fMRI
|
Increased activity in brain areas associated with self-control (anterior cingulate, prefrontal cortex). Significant decrease in smoking (60%) over controls (no reduction).
|
Timmerman & Brown, 2012
|
35
|
Diet, Obesity
|
Perimenopausal women who dine out
|
MRE
|
Waitlist
|
Weight, waist circumference, self-reported daily calorie and fat intake, self-reported calories and fat consumed when eating out, emotional eating, diet related self-efficacy, and barriers to weight management when eating out
|
Significant reduction in weight, lower average daily calorie and fat intake, increased diet-related self-efficacy in treatment group.
|
Vidrine et al., 2016
|
412
|
Smoking
|
Low-income smokers
|
MBAT
|
Usual Care, Cognitive behavioral therapy
|
Nicotine dependence, mindfulness technique practice during treatment, smoking abstinence, relapse
|
No significant overall treatment effects. Significant overall recovery of abstinence.
|
Multiple reports from the same RCT intervention
Daubenmier et al., 2016
|
194
|
Diet, Lipids, Obesity
|
Overweight adults
|
Novel MB-EAT
|
Novel active Control
|
Fasting glucose, triglycerides, waist circumference, C-reactive protein, blood pressure.
|
Significant reduction in triglycerides in mindfulness group over controls.
|
Mason et al., 2016a
|
194
|
Diet, Exercise, Obesity
|
Overweight adults
|
Novel MB-EAT
|
Novel active Control
|
Reward-based eating, psychological stress, and weight
|
Significant reductions in reward-driven eating which predicted weight loss post-intervention.
|
Mason et al., 2016b
|
194
|
Diet, Exercise, Obesity
|
Overweight adults
|
Novel MB-EAT
|
Novel active Control
|
Mindful eating, eating of sweets, and fasting glucose
|
Nonsignificant reduction in sweets consumption.
|
Radin et al., 2020
|
194
|
Diet, Obesity
|
Overweight adults
|
Novel MB-EAT
|
Novel active Control
|
Compulsive eating, stress eating, fasting blood glucose
|
Nonsignificant reduction in weight loss. Significant improvement in fasting blood glucose & weight in participants with high compulsive eating scores.
|
Daubenmier et al., 2011
|
47
|
Diet, Obesity
|
Overweight or obese women
|
Novel MB-EAT
|
Waitlist
|
Mindfulness, psychological distress, eating behavior, weight, cortisol awakening response (CAR), and abdominal fat
|
Reductions in dining out (external eating) in treatment group. Reductions in CAR in obese patients. No between-group difference in weight.
|
Daubenmier et al., 2012
|
47
|
Diabetes, Diet, Obesity
|
Overweight or obese women
|
Novel MB-EAT
|
Waitlist
|
Primary: Telomerase activity. Secondary: correlations of telomerase activity with psychological distress, eating behavior, and metabolic factors
|
No effect on telomerase. Moderate effect on weight loss vs controls.
|
Abbreviations: Brief Mindfulness Practice (Brief-MP), Freedom from Smoking (FFS), Integrated Mind Body Therapy (IMBT), Mindfulness-Based Addiction Treatment (MBAT), Mindful Eating and Living (MEAL), Mindfulness-Based Eating Awareness Training (MB-EAT), Mindfulness Eating for Diabetes (MB-EAT-D), Mindfulness-Based Stress Reduction (MBSR), Mindful Restaurant Eating (MRE), Mindfulness Training for Smokers (MTS), Mind Your Weight (MYW), Whole Health Action Management (WHAM)
Table 3. Overview of Intervention Characteristics (k=30 published reports from 26 distinct trials)
|
Implementation Characteristics
|
Contextual Factors
|
Study
|
Dosage
|
Delivery Method
|
Staff Characteristics
|
Settings, locations, dates/times
|
Participant characteristics
|
Arch et al., 2016
|
A single session of 5-7 minutes
|
In person via headphones. Small groups, but with individual administration at computer.
|
1 male experimenter. No facilitator.
|
College campus under laboratory conditions. Location & dates/times not described.
|
Young (av. 20 yo), college students, mostly male, mixed racial/ethnic background. Average annual family income: 60-70k.
|
Brewer et al., 2011
|
Bi-weekly 1.5 hr sessions over 4 weeks (8 sessions total) with ~30 min of home practice per session
|
In person. Group format. CD used for home practice.
|
Therapist with 13+ years experience in mindfulness
|
Setting/location & times not described. Sessions on Mondays and Thursdays.
|
Majority men (~46 yo), 45.5% racial/ethnic minority. Over half college educated. Half unmarried.
|
Carmody et al., 2012
|
11 weekly classes of 2.5 hours each
|
In person. Group format.
|
Not described.
|
College university teaching kitchen & conference area. Dates/times not described.
|
Men (~69 yo), majority non-Hispanic white. 91% married.
|
Carpenter et al., 2019
|
At least 11 weekly or biweekly sessions of 20-30 min each
|
Telephone.
|
Registered dieticians, health coaches with ≥ 200 hours of training
|
Not described.
|
Majority women (~46 yo), 65% white, college-educated (~94%).
|
Chacko et al., 2016
|
Ten weekly classes with a half-day (4 hour) retreat. Home practice of undescribed length 6 days/wk
|
In person. Group format.
|
Qualified mindfulness instructor
|
Not described.
|
Majority white women (~53yo), college-educated (100%). Income <75k (67%).
|
Corsica et al., 2014
|
Once-weekly 90-minute sessions for 10 weeks. Home practice of 30-45 min daily.
|
In person. Group format.
|
Not described.
|
Not described.
|
Majority women (~45yo); college-educated (m=16.7 years), mixed racial/ethnic diversity.
|
Daubenmier et al., 2011; Daubenmier et al., 2012
|
Nine 2.5-hour weekly classes, one 7-hour retreat day. Home practice 30 minutes/day, 6 days/week.
|
In person. Group format.
|
Not described.
|
Evenings & weekends. Location/setting not described.
|
Majority white women (~40yo). Other demographics not described.
|
Daubenmier et al., 2016; Mason et al., 2016 a, Mason et al., 2016 b, Radin et al., 2020
|
Total of 16 2-2.5 hr sessions (weekly or biweekly). One 6.5 hr retreat. Home practice of 30 min/day, 6 days/week.
|
In person. Group format.
|
Mindfulness meditation instructors with 5 days training in mindful eating, registered dietitian
|
Evenings and weekends. Location/setting not described.
|
Majority white (~47yo) women, educated (69% bachelor’s degree).
|
Davis et al., 2013
|
Six 2-hour weekly classes, one 7-hour retreat day, 30 min of home practice daily.
|
In person. Group format.
|
2 instructors with Master’s level education, equivalent experience with smoking cessation interventions
|
Not described.
|
Majority white men (~22yo). Other demographics not described.
|
Davis et al., 2014a
|
7-hour introductory class, 4 weekly 90 min classes, one 7-hour retreat day, 30 minutes daily home practice
|
In person. Group format.
|
2 instructors who completed 2-day training in MTS and no formal addiction training
|
Not described.
|
77% white men & women (~45 yo). 40% High school or less.
|
Davis et al., 2014b
|
Seven 2.5 hr classes, one 6.5 hr retreat day, 15-30 min home practice daily
|
In person. Group format.
|
Master’s in psychology or PhD in Sociology and no formal addiction training
|
Not described.
|
88.1% white men & women (~45yo) with high school and above (60%).
|
Garrison et al., 2018
|
22 daily modules of 1-15 min
|
Mobile phone app
|
Not described/not applicable
|
Not described/not applicable
|
Majority white women (~43yo). Married (>50%). Educated (87% high school +).
|
Gillman & Bryan, 2020
|
150 min/week for 2 weeks
|
Email
|
Not described/not applicable
|
Not described/not applicable
|
Majority white women (~27yo). Other demographics not described.
|
Ingraham et al., 2017
|
12 weeks. Session number and length not described.
|
In person. Group format.
|
Personal trainer, registered dietician, licensed social worker, clinical psychologist
|
Not described.
|
Majority white, lesbian women (~53yo). Educated (61% college graduates or postgrad). 53% reported incomes <30k.
|
Janes et al., 2019
|
22 daily modules of 1-15 min
|
Mobile phone app
|
Not described/not applicable
|
Not described/not applicable
|
Majority white men & women (~46yo). Majority unmarried, some college or higher.
|
Lotfalian et al., 2020
|
One 20-minute session
|
In person.
|
Researcher.
|
Laboratory setting.
|
Majority black men & women (~40yo), low-income.
|
Miller et al., 2012
|
8 weekly and 2 biweekly 2 1⁄2 hour sessions, home practice 6 days/wk of undetermined length
|
In person. Group format.
|
Facilitators trained in the intervention protocol
|
Not described.
|
Majority white women (~54yo). Married (67%), nearly half college graduates making ≥ 60k annually.
|
Miller et al., 2014
|
8 weekly and 2 biweekly 2 1⁄2 hour sessions, home practice 6 days/wk of undetermined length
|
In person. Group format.
|
Facilitators trained in the intervention protocol
|
Not described.
|
Majority white women (~54yo). Married (67%), nearly half college graduates making ≥ 60k annually.
|
Raja-Khan et al., 2017
|
8 weekly 2.5 hr sessions & one 6-hr retreat day. 25-30 min home practice
|
In person. Group format.
|
Professional MBSR training, 9 years experience
|
Not described.
|
Majority white women (~45yo). Other demographics not described.
|
Ruscio et al., 2015
|
1 guided meditations per day (5 total)
|
Via Personal Digital Assistant
|
Not described.
|
Naturalistic environment.
|
Demographics not described.
|
Singh et al., 2014
|
4 week baseline at 5-45 min. 36 week intervention from 20-50 min
|
In person (small group) or via Skype
|
Trainer with 35 years experience with intellectual disability and personal mindfulness practice.
|
Variable.
|
Majority men (~33yo). Other demographics not described.
|
Smith et al., 2018
|
6 weekly 2-hr meetings. Home practice of undetermined length/frequency.
|
In person. Groups up to 20 subjects.
|
Not described.
|
Not described.
|
Women (~58yo). Demographics not described.
|
Spadaro et al., 2018
|
One hour weekly for 6 months.
|
In person. Group format.
|
Co-investigator doctoral student in exercise physiology with significant experience, training, and on-going supervision in weight loss interventions
|
Tuesday evenings. Location/setting not described.
|
Majority white women (~45 yo), educated (46% bachelor’s and above).
|
Tang et al., 2013
|
10 sessions of 30 minutes over 2 weeks
|
In person. Group format.
|
Not described.
|
Evenings. Setting/location not described.
|
Young (~21yo). Demographics not described.
|
Timmerman & Brown, 2012
|
6 weekly 2-hour sessions
|
In person. Group format.
|
Not described.
|
Not described.
|
Women (~50yo), over half white. Educated (89% some college), most over 50k annual income.
|
Vidrine et al., 2016
|
8 weekly 2-2.5 hour sessions. Home practice of 30 min daily.
|
In person. Group format.
|
Described as therapists. No other detail.
|
Not described.
|
Nearly half black (48.2%), over half women. Unmarried (70%), with high school diploma or less (one third), most making <30k annually
|
Primary Study Findings.
Primary outcomes for each study are reported in Table 2 and summarized here briefly. Mindfulness-based interventions produced positive results in smoking outcomes. Two studies reported a statistically significant reduction in smoking over controls [58-59]. Another two studies found smoking abstinence outcomes superior in the treatment group [48, 54, 59, 64] while others found comparable between-group outcomes for smoking reduction [49] and abstinence [42, 49-50]. Reductions in craving were also observed [42, 49-50, 54, 58] and support for the effect of MBI on craving was demonstrated by a reduction in brain activity related to smoking cues, correlated to an overall reduction in cigarette consumption in the intervention condition [53]. Additionally, brain areas relating to self-control (the anterior cingulate and prefrontal cortex) showed increased activity with meditation, and demonstrated a 60% reduction in smoking, with no reduction shown in the control group [62].
Positive dietary changes and/or changes in eating behaviors associated with MBI were supported in numerous studies [41, 44-46, 52, 55, 61, 69] and decreases in emotional eating behavior were reported in 3 studies [44-45, 68]. Reductions in dining out were reported in one study [69]. Treatment was also found to produce nonsignificant reductions in the consumption of sweets [67]. Reductions in cholesterol levels were observed in 2 studies [52, 65].
Mindfulness was found to be as effective as a standard diabetes self-care treatment in one study [56] and produced significant decreases in fasting glucose levels compared with controls [57]. Significant increases in HbA1C concentrations—a test which reveals average blood sugar over 2-3 months—were found in the mindfulness group in one study [45] and nonsignificant between-group outcomes were reported in another [55]. Finally, significant improvements in fasting blood glucose were found in participants with high compulsive eating scores post-intervention [68].
Weight loss or maintenance was reported for MBI to varying degrees, with some studies producing greater results than control interventions [46, 55, 68-69] and others found nonsignificant between-group improvements [44-45, 56-57, 60]. Mindfulness was found to improve positive affective response to exercise but did not increase minutes exerted relative to controls [51]. Weight loss was also found to be predicted post-intervention by reductions in reward-based eating [66].
The included pilot feasibility studies found MBI feasible and acceptable for weight loss [44], emotional eating [45], dietary changes in prostate cancer patients [43], and smoking abstinence [48]. While both the benefits and the feasibility and acceptability of mindfulness-based interventions in American minorities is understudied, the research presented in this review points to potential benefits of MBI as a treatment option for CVD risk and provides a basis for future research in this area.
Oxford Implementation Index: Implementation characteristics.
Table 3 presents information extracted from primary studies regarding implementation characteristics of the primary studies. Dosage varied widely across studies, with the majority closely modeled after the multi-week, multi-hour model set forth by MBSR and its contemporaries. Program length ranged between 1 day and 6 months, with k=24 studies consisting of ≥6 sessions. Session durations ranged between 5 minutes and 7 hours. Dates and times of program delivery remained largely undescribed. Thirteen studies reported home practice of between 15-45 minutes for between 5-7 days per week. Delivery method was largely in-person in a group setting (k=19), with 2 delivered in person individually, and 5 delivered remotely or digitally. Staff characteristics—which were at least partially detailed in 16 studies—were universally described in terms of vocation and training, with no descriptive characteristics of the staff/providers described in the primary studies (age, racial/ethnic background). No proscribed/incompatible activities or details of meetings/communication between staff were reported. Numerous studies reported differences between trial arms which did not directly relate to the research question of this review and are therefore not outlined herein.
Several sources of possible contamination were found. In nearly all studies, previous interest in, knowledge of, or experience with mindfulness was not controlled for or was not described. One study excluded participants’ current or recent (previous 6 months) mindfulness or meditation practice [45], another explicitly excluded participants with prior participation in a mindfulness program [46] and two [69-70] excluded participants with prior MBSR experience or a current meditation or yoga practice. Additionally, it was unclear in most studies if recruitment or screening materials mentioned mindfulness or meditation, which may contribute to self-selection. Two studies [48, 60] avoided mention of mindfulness in recruitment materials to avoid potential self-selection or the contamination of the control group. One study [58] lists the mention of mindfulness as a limitation. Two additional studies listed limitations for not excluding based on prior mindfulness experience [58] or not screening for prior exposure [62]. Finally, one study [64] did include subjects with previous experience which they report did not impact findings. Additional potential sources of contamination existed in several studies.
Another potential source of contamination was observed in most studies, such that it was unclear if the experimenter also served as a facilitator for either treatment or control group, which could create demand effects. In one study [61] the facilitator was described as being a co-authoring doctoral student. An additional source of contamination was found in two studies which focused on low-SES smokers. These studies explicitly stated that participants could not be blinded, as many participants “worked odd hours” and it was necessary to allow them to decline if they could not attend all sessions [48-49]. This lack of blinding may bias study results to favor participants with the ability to attend sessions, and points to a potential structural barrier to engaging with in-person, group-based mindfulness interventions in low-SES individuals.
Oxford Implementation Index: Contextual factors.
Table 3 presents contextual factors extracted from primary report that were deemed relevant to this review. Setting, geographic location, and dates/times were at least partially described in 10 studies. Three reported campus or laboratory settings [41, 43, 54] and two reported home or naturalistic settings [51, 58]. The other sixteen studies provided no description of these factors. Participant characteristics were at least partially described in 22 studies (see Table 3). A total of 17 studies reported majority white participants, with 5 reporting mixed race or majority black, and 4 not reporting participant demographics (see Table 2).
Other salient characteristics were partially described (see Table 3). Median age ranged from 20-69 across all studies. Women were disproportionately represented in 15 studies (>50% female), 5 studies reported over 50% males, and 4 studies had a combination of the two. Gender identity was not reported in any study, and LGBTQ+ demographics were considered in one study [52], which consisted of lesbian participants. Educational attainment was reported in 15 studies and revealed that the majority of recruited participants had at least some college education (11 studies). Income was only described in seven studies, five of which were comprised of participants making >50k annually. Three studies specifically focused on low-SES participants [48-49, 64], though two of these studies did not describe income-based inclusion criteria or annual income for participants, instead focusing on “low-income neighborhoods” during recruitment [48-49].
In addition to these factors, it should be noted that the majority of studies were described as being in the early stages of research, either as preliminary research or pilot trials. This may account for many commonly reported limitations including small sample sizes, convenience sampling, high attrition rates, and lack of generalizability. Future research will need to address these limitations, and reasons for attrition should be explored vis-à-vis racial and ethnic background.