Glycemic Improvement and Health Equity in the National Diabetes Prevention Program

The National Diabetes Prevention Program (NDPP) is a yearlong lifestyle intervention to prevent diabetes through weight loss. However, only 28% of participants achieve ≥5% weight loss, and there are concerning disparities based on age, sex, race, ethnicity, and socioeconomic status (1). Alternatively, new guidelines from the Centers for Disease Control and Prevention (CDC) target ≥0.2% HbA_1c improvement for participants with prediabetes (2), but the likelihood of reaching this goal is unknown. We report on the frequency and predictors of achieving ≥0.2% HbA_1c improvement in the NDPP.

The NDPP was implemented in a safety net health care system from 2013 to 2018 following CDC guidelines. Participants included 1,171 adults with overweight/obesity and prediabetes, past gestational diabetes, or an elevated score on the CDC’s Prediabetes Risk Test. Among 832 participants with prediabetes (i.e., HbA_1c 5.7–6.4% within 1 year before starting the NDPP), 535 had HbA_1c testing within 1 year after participation by which to examine pre–post change. The other 297 participants with prediabetes lacked follow-up HbA_1c testing, which is often conducted in clinical care but not required in the NDPP. HbA_1c, height, and demographics, including age, sex, race, ethnicity, and insurance (a proxy of socioeconomic status), were collected from medical records. Weight was recorded at each session attended. Self-reported physical activity (weekly minutes) was recorded after activity tracking was introduced in the second month of intervention.

We first assessed differences in the frequency of follow-up HbA_1c testing by demographics, baseline BMI, baseline HbA_1c, weight loss, physical activity, and attendance. Multiple logistic regression models then estimated covariate-adjusted differences in achieving ≥0.2% HbA_1c improvement by demographics and levels of weight loss (≥5% or <5%), physical activity (≥150 or <150 min per week on average), and attendance (≥9 or <9 months). Covariates included demographics and baseline BMI and HbA_1c, weight loss, and attendance in corresponding models. Sensitivity analyses further controlled for physical activity, which was available for 305 participants. The Colorado Multiple Institutional Review Board approved this program evaluation project (16-1093).

Participants with or without follow-up HbA_1c testing were similar in sex, race, ethnicity, weight loss, BMI, and physical activity. There were significant differences in mean age (51.8 ± 0.5 vs. 47.8 ± 0.72 years; P < 0.001), baseline HbA_1c (6.02% ± 0.01 vs. 5.97% ± 0.01; P = 0.003), and duration of attendance (4.0 ± 0.2 vs. 3.2 ± 0.2 months; P = 0.007). Medicare beneficiaries also had more follow-up HbA_1c testing (75.6%) than participants with other insurance types (64.3%; P = 0.015).

Participant characteristics and outcomes are shown in Table 1 for the main analysis. Nearly half of participants (45.0%) achieved ≥0.2% HbA_1c improvement. Non-Latinx Black participants were 40% as likely as non-Latinx white participants to achieve ≥0.2% HbA_1c improvement. There were no significant disparities by sex, age, or insurance. Participants with ≥5% weight loss were 2.5× more likely to achieve ≥0.2% HbA_1c improvement than those with <5% weight loss. Average weight loss was 2.2% (SD 3.9) and 1.1% (SD 3.2), respectively, among participants with and without ≥0.2% HbA_1c improvement. Neither physical activity nor attendance was a significant predictor of ≥0.2% HbA_1c improvement. Results were consistent in sensitivity analyses.

In conclusion, the NDPP appears to be an effective intervention with equitable impact across sex, age, and socioeconomic groups when evaluating HbA_1c improvement instead of weight loss. Our findings align with new evidence that the NDPP reduces diabetes incidence by 46% in diverse populations, even without sustained weight loss (3). As diabetes is defined by hyperglycemia, not weight, it is unsurprising that lowering glucose can prevent diabetes. Implications for health policy change include reimbursing NDPP suppliers for HbA_1c outcomes, whereas current payment models prioritize weight loss (1). Although equitable HbA_1c outcomes were observed for Latinx participants, it is concerning that Black participants were least likely to achieve ≥0.2% HbA_1c improvement. More effort appears needed to ensure fully equitable outcomes and help even more participants reach or surpass this threshold. Strategies may include using flexible goal setting as an alternative to the NDPP’s current emphasis on preset goals (4). Flexible goal setting appeared key to help women, younger adults, low-income participants, and Latinx and Black participants achieve ≥0.2% HbA_1c improvement (5). Another important finding is that attending the NDPP for ≥9 months appears less necessary for beneficial outcomes than previously thought (1), which raises the possibility of shortening the program to increase capacity and appeal to potential participants who are deterred by a lengthy intervention. However, results are not generalizable, and further study is needed with nationally representative samples. Efforts to help all participants complete HbA_1c testing may also facilitate better clinical care and provide an opportunity for more rigorous evaluation of the NDPP.