Effectiveness of text message-delivered health behaviour intervention on HbA1c change in adults with type 2 diabetes mellitus: a systematic review and meta-analysis of randomised controlled trials.

This study aims to investigate the effectiveness of text message-delivered health behaviours intervention on HbA1c change among adults with T2DM, and to identify key moderators including intervention features, message characteristics, target behaviours, and the usage of behaviour change techniques (BCTs). We systematically reviewed 37 randomised controlled trials published between 2016 and 2025, involving 8,971 participants. Changes in HbA1c and health behaviours were analysed using the standardised mean difference. The meta-analysis revealed a significant reduction in HbA1c (g = -0.32, 95% CI = -0.46 to - 0.18). Meta-regression also found that the intervention significantly improved health behaviours, which in turn predicted a significant reduction in HbA1c levels. Subsequent subgroup analyses revealed that studies with a shorter duration (≤6 months) demonstrated a larger effect size in reducing HbA1c. Notably, interventions employing specific BCTs including 'body changes' (g = -0.643), 'habit formation' (g = -0.624), 'credible source' (g = -0.513), 'self-monitoring of outcomes of behaviours' (g = -0.377), and "instruction on how to perform the behaviour' (g = -0.354) were significantly associated with greater HbA1c reductions. These effects were particularly pronounced in trials focused on physical activity, healthy eating, and medication adherence. Conclusions suggest that text message-delivered health behavior interventions should be tailored to specific target behavior and incorporate these high-impact BCTs to comprehensively improve diabetes management.