Achieving behavior change at scale: Causal evidence from a national lifestyle intervention program for pre-diabetes in the UK.

There remains widespread doubt among clinicians that mere lifestyle advice and counseling provided in routine care can achieve improvements in health. We aimed to determine the health effects of the largest behavior change program for pre-diabetes globally (the English Diabetes Prevention Programme) when implemented at scale in routine care. We exploited the threshold in glycated hemoglobin (HbA1c) used to decide on program eligibility by applying a regression discontinuity design, one of the most credible quasi-experimental strategies for causal inference, to electronic health data from approximately one-fifth of all primary care practices in England. Program referral led to significant improvements in patients' HbA1c and body mass index. This analysis provides causal, rather than associational, evidence that lifestyle advice and counseling implemented in a national health system can achieve important health improvements.