Study selection and characteristics
The updated literature search identified a total of 1226 unique publications, of which 17 individual RCTs were identified and full texts screened for potential eligibility. We ultimately included 14 papers (see Additional file 2 for an overview). The included studies were conducted in 7 countries: USA (27, 28, 30-35), Croatia (36), Sweden (37), Iran (38), Turkey (39), Greece (40) and Taiwan (29) and were published from 2010 to 2019. The characteristics of the included studies are reported in Table 1.
Participant characteristics
The overall mean age of the participants (n= 1,378) included in the studies was 58.1 (SD ± 4.7), of which 50.9% were female, mean a BMI was 32.5 (SD ± 4.6). The most common combination of conditions reported was type 2 diabetes and depression in 6 studies (27, 29, 30, 33, 35, 36), diabetes and heart failure in 5 studies (28, 32, 38-40), type 2 diabetes and heart failure in 2 studies (31, 37) and hypertension and type 2 diabetes in one study (34).
Intervention and comparator groups characteristics
All the interventions targeted lifestyle behaviours, including physical activity and healthy diet. The interventions were multifaceted and, in addition to usual care (e.g. counselling from their health care provider), the most commonly used components were exercise therapy in 8 studies (27, 32, 35-40), cognitive behavioural therapy (CBT) in 4 studies (27-29, 32), patient education in 3 studies (27, 32, 36), self-care in 2 studies (31, 33), and motivation enhancement therapy (29), pharmacology (33) and behavioural activation (35) in one study. Exercise together with patient education and CBT or behavioural activation, were used in 3 studies (27, 32, 35).
The comparator groups included usual care (e.g., counselling from their health care provider), psychoeducation, and CBT (Table 1). However, for the meta-analysis the comparator groups included were usual care groups.
The BCTs used in the included studies to target lifestyle behaviours such as physical activity and weight loss are reported in Additional File 3. Overall, the BCTs most commonly used were ‘Instructions on how to perform the behaviour’ (BCT 4.1) in all the studies but one (33), ‘Social support unspecified’ (BCT 3.1) in 11 studies (27-29, 31-35, 38, 39) and ‘action planning’ (BCT 1.4) in 9 studies (27, 28, 30, 32, 35, 37-40). The clusters of BCTs most commonly used were ‘Goals and planning’ and ‘Feedback and monitoring’ which were present 27 times in the 14 included studies.
Outcome characteristics
Physical activity was reported in 8 studies (28, 30, 31, 33-35, 39, 40), of which 5 used an objective assessment (e.g. accelerometer) (28, 30, 35, 39, 40) and 3 a self-reported tools (31, 33, 34). Weight loss was reported in 6 studies (27-29, 34, 35, 40) of which 5 studies reported data about the BMI of the participants and one as Kg (34). Physical function was reported in 7 studies (27, 28, 30-32, 37, 38) of which 5 studies used an objective assessment (i.e. the 6 minutes walking test) (27, 28, 31, 32, 37) and two used a self-reported tool (i.e. the SF-12) (30, 38). Health-related quality of life was reported in 10 studies (27-33, 37, 39, 40). Characteristics of the outcome measures are reported in Table 1.
Effect of behavioural interventions on physical activity
Five studies were included in the meta-analysis on physical activity. At the end-treatment follow-ups (mean 16 weeks (SD ± 4)), behavioural interventions appeared to have little effect on objectively measured physical activity (SMD 0.38, 95% CI -0.12 to 0.87; I2 = 83.6%) (Figure 1), however, the evidence is uncertain. Only one study (35) reported data on long term-follow ups (24 weeks post randomisation), showing no difference on objectively measured physical activity between the intervention and comparator group (SMD 0.13, 95% CI -0.58 to 0.84).
Three studies assessed self-reported physical activity (31, 33, 34). The results of these three studies were summarised narratively as no meta-analysis was deemed eligible due to large differences in reporting of the self-reported physical activity outcome measures. Overall, these three studies reported that the participants in the intervention groups were more physically active than the participants in the control groups at the end-treatment follow-up (mean 33 weeks, SD ± 16). One study (31) reported that the percentage of participants physically active (i.e. having a Community Healthy Activities Model Program for Seniors (CHAMPS) questionnaire score >6) was 74.5% in the intervention group and 59.5% in the comparator group. Another study (33) reported that the percentage of participants physically active (two or more times per week) was 68.5% in the intervention group and 32.5% in the comparator group. While yet another study (34) reported that the participants in the intervention group improved their physical activity level (assessed with the CHAMPS questionnaires) more than the comparator group (P < 0.05).
BCT associated with physical activity (objectively measured and self-reported).
Overall, 12 BCTs were reported in at least 3 study comparisons at the end-treatment follow-up, and effectiveness ratios were calculated. Ten of the 12 BCTs tested had an effectiveness ratio of more or equal to 75%, with the BCT 3.2 ‘social support (practical)’ and BCT 1.4 ‘action planning’ having an effectiveness ratio of 100% (Figure 2). At the follow-up closest to 12 months, we were unable to calculate effectiveness ratios due to insufficient data. Additional file 4 reported the raw data for calculating the effectiveness ratios.
Effect of behavioural interventions on weight loss
Five studies were included in the meta-analysis on weight loss (27-29, 35, 40) with end-treatment follow-ups (mean 18 weeks (SD ± 7). It is uncertain whether behavioural interventions have an effect on weight loss (BMI mean difference -0.17, 95% CI -1.17 to 0.83: I2=13.3%) (Figure 3). The study not included in a meta-analysis reported that the intervention group lost 1.8 kg (95% CI -4.3 to 0.8) more than the comparator group (34).
Two studies were included in the meta-analysis with long term follow-ups (24 months post randomisation) (29, 35) showing uncertainty for the effect of behavioural interventions on weight loss (BMI mean difference -0.54, 95% CI -2.70 to 1.62; I2=0.0%) (Additional file 4).
BCT associated with weight loss
Overall, 11 BCTs were reported in at least 3 study comparisons, and effectiveness ratios were calculated. Five of the 11 BCT tested had an effectiveness ratio of more or equal to 75%, with the BCT 3.2 ‘social support (practical) and BCT 1.4 ‘action planning’ having an effectiveness ratio of 100% (Figure 4). At the follow-up closest to 12 months, we were unable to calculate effectiveness ratios due to insufficient data. Additional file 4 reports the raw data for calculating the effectiveness ratios.
Effect of behavioural interventions on health-related quality of life
Ten studies were included in meta-analysis on health related-quality of life at the end-treatment follow-up (mean 17 weeks (SD ± 13)). Behavioural interventions improved health-related quality of life (SMD 0.29, 95% CI 0.17 to 0.42: I2=0.0%) (Figure 5). Three studies were included in the meta-analysis with long term follow-ups (24 months post randomisation) (28, 29, 32) and one study was included in the narrative synthesis. Meta-analysis showed that behavioural interventions may improve health-related quality of life (SMD 0.20, 95% CI -0.05 to 0.46; I2=0.0%). However, the evidence was uncertain (Additional File 5), and the study included in the narrative synthesis showed no difference between the intervention and comparator group (36). We did not conduct meta-regression analyses or effectiveness ratio for health-related quality of life due to the non-existing statistical heterogeneity of the meta-analysis.
Effect of behavioural interventions on physical function
Eight studies were included in meta-analysis for physical function at the end-treatment follow-up (mean 12 weeks (SD ± 5)). Behavioural interventions improved physical function (SMD 0.42, 95% CI -0.12 to 0.73: I2=69.5%) (Figure 6). Meta-regression analysis showed that increasing age was associated with higher effect sizes (slope 0.07, 95% CI 0.02 to 0.13) explaining 65% (Adjusted R2) of the inconsistency of the findings. A higher proportion of female participants in the studies was associated with lower effect sizes (slope -0.02, 95% CI -0.04 to -0.01) explaining 36% (Adjusted R2) of the inconsistency of the findings. Meta-regression analysis also showed that studies using the BCT 2.1 ‘Monitoring of outcome of behaviour by others without feedback’ were associated with a lower improvement in physical function than studies not using this BCT. Additionally, meta-regression analysis showed that studies using a higher number of BCTs for ‘goal setting and planning’ were associated with lower effect sizes (slope -0.45, 95% CI -0.72 to -0.18) this explained 87% of the variations in the results of the meta-analysis (Additional File 6). Finally, a sub-group analysis showed that behavioural interventions including structured exercise session reported a moderate and possibly clinically relevant improvement (SMD 0.56, 95% CI 0.08 to 1.04) compared to interventions without a structured exercise session (SMD 0.25, 95% CI –0.06 to 0.56) (Additional File 7).
One study, including two study comparisons, was included in the meta-analysis with long-term follow-up (24 weeks post randomisation). The study assessed physical function with the 6 minutes walking test and showed that behavioural interventions improved physical function (mean difference in meters walked in 6 minutes: 74.9, 95% CI 0.01 to 149.9; I2=0.0%).
Additional analyses
Eleven studies were included in the additional analysis investigating the effect of behavioural interventions on depression symptoms. At the end-treatment follow-ups (mean 14 weeks (SD ± 6)) behavioural interventions reduced depression symptoms (SMD -0.70, 95% CI -0.98 to -0.42: I2 = 74.8%) (Figure 7). At the long-term follow-up assessment there was no effect of behavioural interventions on depression symptoms (SMD -0.38, 95% CI -1.02 to 0.26: I2 = 89.9%). Meta-regression analysis showed that studies including people with a higher BMI (slope 0.9, 95% CI 0.04 to 0.15), studies using a higher number of BCTs for ‘goal setting and planning’ (slope 0.31, 95% CI 0.04 to 0.58) and ‘Feedback and monitoring’ (slope 0.25, 95% CI 0.02 to 0.48) were associated with a lower reduction of depression symptoms. Depression severity at baseline was not associated with depression symptoms reduction (slope 0.01, 95% CI -0.02 to 0.03).
Sensitivity analyses
In the sensitivity analyses analysing physical activity and physical function together, 10 studies (12 comparisons) were included. At the end-treatment follow-ups (mean 14 weeks (SD ± 6)) behavioural interventions improved physical activity and physical function when combined (SMD 0.45, 95% CI 0.16 to 0.73: I2 = 69.6%) (Figure 8).
Ten studies were included in the sensitivity for health-related quality of life (i.e., including the mental component scale data instead of the physical component score data for the studies using the SF-12). At the end-treatment follow-up, (mean 17 weeks (SD ± 13)) behavioural interventions improved health-related quality of life (SMD 0.30, 95% CI 0.15 to 0.44: I2=0.0%) (Figure 9). These results are similar to the primary analysis results (Figure 6).
Risk of bias and overall quality of the evidence
The majority of the RCTs applied a proper randomisation process and reported and assessed the outcomes of interest correctly. Due to the nature of behavioural interventions, blinding of participants is challenging as patients receiving the intervention are also the outcome assessors of the patient-reported outcomes (Additional file 8). The overall quality of the evidence assessed using GRADE, including reasons for downgrading the quality of the evidence, is summarised in Table 2.