The U.S. National Diabetes Prevention Program (NDPP) Shows Promise as a Cost-effective Implementation Strategy Free

Around 36 million U.S. adults have type 2 diabetes, and 2 million more develop it annually (1). Without detection and glucose-lowering treatment, type 2 diabetes causes silent and progressive damage before surfacing, often years later, with symptoms or complications. Intensive glucose and cardiovascular risk factor management slow complications, but treatments are burdensome for patients, increase medical costs, and do nothing to stem the growing tide of new cases. The percentage of U.S. adults with type 2 diabetes has grown twofold over the past 35 years (2), adding financial burden for patients, employers, and all who share in the financing of U.S. health care. Without cost-effective primary prevention strategies, the toll of diabetes will continue to escalate.

Landmark trials such as the U.S. Diabetes Prevention Program (DPP) demonstrated that intensive lifestyle interventions cut the rate of progression to type 2 diabetes in half (3) and can be more effective, safer, and cheaper than medications that prevent or delay type 2 diabetes through weight loss or other mechanisms (4,5). Intensive lifestyle interventions involve recurring behavioral coaching to improve nutrition, increase physical activity, and achieve modest weight loss, all of which have health benefits beyond diabetes prevention, such as improved cardiovascular risk factor control, less arthritis pain, lower risk of falls, and better sleep and mood. Collectively, these outcomes have the potential to reduce health care use and costs through many mechanisms.

The National Diabetes Prevention Program (NDPP) is a U.S. federal investment in strategies to bring DPP-like interventions to millions of high-risk adults with prediabetes (6). The Centers for Disease Control and Prevention (CDC) administers NDPP, defines benchmarks for intervention fidelity and performance monitoring, and supports interventionist training and capacity building for delivery organizations in all 50 states. The CDC’s recognition confirms for third-party health payers when an organization is supplying a high-fidelity and high-performing NDPP intervention. Compared with clinical trial interventions, the NDPP allows programs to target adults at lower risk of progression to diabetes and to offer lower-intensity coaching (16 vs. 26 contact hours in the DPP trial and often in group settings rather than one-on-one coaching) over a shorter duration (typically about 1 year rather than ongoing) (7). Past studies of similar lower-intensity adaptations of the DPP demonstrated mean weight loss outcomes of ∼50–75% of the magnitude achieved in the DPP (8) for about 25% of the delivery cost (4). NDPP has reached nearly 1 million Americans across 50 states, with intervention services offered by 1,500 recognized delivery organizations. One prevailing question is whether NDPP is cost-effective.

In this issue of Diabetes Care, Kuo et al. (9) report on their evaluation of medical costs for adults with prediabetes before and after receiving free-of-charge access to NDPP services funded by an employer-sponsored health insurance plan. The health plan used billing data to identify enrollees with recent medical encounters where prediabetes was listed as a visit diagnosis, and it sent those enrollees letters encouraging them to take part in NDPP services offered in different formats and settings. About 10% of the target population was motivated and able to enroll in NDPP services. Compared with nonresponders, the participants were more likely to be older, women, of non-White race, and had modestly higher BMI and HbA_1c, all of which predisposed them to develop type 2 diabetes faster than nonparticipants. Because the NDPP participants and nonparticipants began with different levels of risk for diabetes development, the investigators used a natural experimental research design to avoid making false conclusions about the effects of NDPP services.

Kuo et al. used the method of inverse propensity–weighted estimation; individuals who had characteristics making them less likely to start treatment received less weight in the estimation. Weighted characteristics of the study population, found in Table 1 of their article, describe people most likely to take up NDPP when encouraged by their health plan. The weighted characteristics of each group should be similar, as if individuals had in fact been randomly assigned to treatment. Table 1 shows the balance of most characteristics predictive of future diabetes development, although pretreatment health care expenditures remained modestly higher ($930 higher) for the treated group.

Kuo et al. found that NDPP participants had lower mean medical expenditures over the 2 years after starting the intervention. The cost differences were not statistically significant, in part because of wide SD in costs for both groups, which is common in medical expenditure data. Interestingly, the cost analysis did not show increasing costs in medication expenditures, diagnostic costs, or specialty visits, which we might anticipate for adults with obesity-related conditions like prediabetes. Instead, mean costs for both groups decreased after the intervention period began, and the decrease was larger for those who used NDPP services, driven by lower inpatient, outpatient, or emergency department costs.

This cost pattern might be explained by how the target population was identified, which required an insurance claim for a recent inpatient or outpatient visit where a prediabetes diagnosis was documented. We know very little about the reasons for documenting prediabetes at some visits and not others, but we do know that another health problem likely drove most patients to the doctor in the first place (>80% of U.S. doctor’s office visits are problem-focused) (10), and the decision to document prediabetes at a visit implies that it was somehow relevant to those health problems. All patients likely left those baseline visits with treatment plans, resulting in fewer return visits (and lower costs) over the coming months. Importantly, those who took action to address prediabetes by participating in NDPP used health care even less than those who did not participate.

Consistent with prior reports, the analysis by Kuo et al. found statistically significant and meaningful differences in the cumulative incidence of diabetes for those who engaged in prevention programs. The absolute risk difference of 2.8% translates to a number needed to treat of 36 people for 2 years to prevent one case of diabetes. Past studies show excess costs of $3,300–8,300 per person during the first year after a new type 2 diabetes diagnosis and $2,900–3,800 annually thereafter (11–13). If such costs were avoided by just 1 in every 36 NDPP participants, the net effect on mean health care costs would be insufficient to explain the total cost difference reported by Kuo et al. One plausible explanation is that increased physical activity and weight loss by NDPP participants prevented health care visits for other problems, such as knee pain, poor sleep, or other symptoms shown to improve with healthy lifestyle changes. Another explanation could be that, in the absence of NDPP, nonparticipants returned to their doctors more often to seek other services, such as nutritional education or obesity counseling. Further research will be needed to understand differences in the patterns of health care use between NDPP participants and nonparticipants.

The study by Kuo et al. contributes important new findings regarding U.S. efforts to slow the health and economic toll of type 2 diabetes. Although NDPP services are lower in intensity and duration than clinical trial interventions, efforts by the CDC and others to support NDPP delivery and fidelity are supplying the health system with services that have clinically meaningful effects on diabetes progression. Moreover, health plans play important roles in identifying high-risk populations for whom offering NDPP as a health insurance benefit is likely to 1) improve health in ways that lower the need for other health services and 2) reduce total health care expenditures over a relatively short, 2-year time horizon.