The Diabetes Prevention Program (DPP) was a multicenter trial examining the ability of an intensive lifestyle program or treatment with metformin to prevent or delay the development of type 2 diabetes in high-risk individuals with prediabetes. The DPP study showed that both interventions reduced the incidence of diabetes in participants, compared with placebo; the lifestyle intervention proved more effective than metformin in preventing the onset of diabetes. The Diabetes Prevention Program Outcomes Study (DPPOS) is the long-term follow-up of the original DPP study. The DPPOS sought to evaluate the effects of the interventions on the further development of diabetes and diabetes complications, including retinopathy, microangiopathy, and cardiovascular disease.

All active DPP participants were eligible for continued follow-up, and 88% of DPP participants enrolled in DPPOS (910 participants from the lifestyle, 924 from the metformin, and 932 from the original placebo groups). On the basis of the benefits from the intensive lifestyle intervention in the DPP, all three groups were offered group-implemented lifestyle intervention. Placebo was discontinued in the placebo group, metformin treatment was continued in the original metformin group, with participants unmasked to assignment, and the original lifestyle intervention group was offered additional lifestyle support. Comprehensive annual and semi-annual assessments similar to those done in the DPP study continued in DPPOS and included physical measurements, medical history updates, adverse event assessment, medication adherence and dispensing, questionnaires, and an annual oral glucose tolerance test (OGTT). OGTTs were discontinued after a confirmed diagnosis of diabetes.

DPPOS found that prevention or delay of diabetes with lifestyle intervention or metformin can persist for at least 10 years; the cumulative incidence of diabetes remained lowest in the lifestyle group.

Data collected after the final DPP Bridge visits in 2002 through February 2020 are available from the Repository.

The objective of DPPOS was to evaluate the effects of the DPP interventions on the further development of diabetes and diabetes complications, including retinopathy, nephropathy, neuropathy, cardiovascular disease, and cancer.

The primary outcome measure of the first phase of DPPOS (2002-2008) was development of diabetes according to American Diabetes Association criteria. The primary outcome of the second phase of DPPOS (2008-2013) was the prevalence of a composite microvascular outcome. Secondary outcome measures included the development of cardiovascular disease. The primary outcomes of the third phase of DPPOS (2014-2020) were incident cancer and cardiovascular disease.

All active DPP study participants were eligible for continued follow-up, including those with and without diabetes. Of the active participants at the end of the DPP study, 88% enrolled in the follow-up cohort.

The study found that prevention or delay of type 2 diabetes with lifestyle intervention or metformin in a high-risk population, as seen in the DPP study, can persist for at least 10 years. After an average of 10 years’ follow-up, intensive lifestyle changes aimed at modest weight loss reduced the rate of developing type 2 diabetes by 34%, delayed type 2 diabetes by about 4 years, and reduced cardiovascular risk factors, hemoglobin A1c, and fasting glucose when compared with placebo. Additional findings after 10 years’ follow-up showed that treatment with metformin reduced the rate of developing diabetes by 18%, delayed diabetes by 2 years, and reduced hemoglobin A1c and fasting glucose when compared with placebo.

Diabetes prevention effects in the original lifestyle group and metformin treatment groups persist 22 years after the start of DPP with a 25% and 18% reduced risk of diabetes development, respectively, compared with the original placebo group. There were no overall differences in the aggregate microvascular outcome between treatment groups through DPPOS Phase 2 (~15 years); however, those who did not develop diabetes had a 28% lower prevalence of microvascular complications than those who did develop diabetes. Over more than 20 years through DPPOS Phase 3, neither metformin nor lifestyle intervention reduced major cardiovascular events or cancer incidence despite long-term prevention of diabetes.