We previously demonstrated that the DPP lifestyle and metformin interventions were more expensive than placebo intervention (7
). Yet, delaying or preventing type 2 diabetes delays or prevents the direct medical costs of diabetes, including the costs of diabetes education and nutritional counseling, glucose monitoring, treatment, surveillance for complications, and treatment of complications. It also improves quality of life and length of life. We recently demonstrated that from the perspective of a health system over 3 years and relative to the placebo intervention, the lifestyle and metformin interventions cost $16 000 and $31 000 per case of diabetes prevented and $32 000 and $100 000 per QALY, respectively (8
). Adopting a 3-year time horizon overestimates treatment costs and underestimates the benefits of the lifestyle and metformin interventions (8
). In this paper, we aimed to extend the results of our previous analyses and project the costs, health out-comes, and cost-effectiveness of the lifestyle and metformin interventions relative to the placebo intervention over a lifetime.
In these analyses, we used a previously developed and published simulation model (11
). We modified this simulation model to include progression from impaired glucose tolerance to diabetes, recognize the 10-year delay between the onset and clinical diagnosis of type 2 diabetes, incorporate new data describing costs and health utility scores, and incorporate the most recently published data from the UKPDS on the development and progression of complications among intensively treated patients with type 2 diabetes.
Compared with the placebo intervention, the lifestyle and metformin interventions produced clinically meaningful reductions in type 2 diabetes and its microvascular, neuropathic, and cardiovascular complications. Our projections presented in the Figure indicate that the lifestyle and metformin interventions can delay and prevent type 2 diabetes by forestalling its onset by several years and reducing its cumulative incidence.
From the perspective of a health system, the lifestyle intervention was highly cost-effective, costing only $1100 per QALY, and the metformin intervention was in a generally cost-effective range, costing approximately $31 300 per QALY. The lifestyle intervention, compared with the metformin intervention, cost less and resulted in better health outcomes. In sensitivity analysis, we observed important differences by age. Whereas the lifestyle intervention was cost-saving in participants younger than 45 years of age and was cost-effective even in the oldest age groups, the metformin intervention was not cost-effective in participants older than 65 years of age. Otherwise, the results were robust to plausible changes in implementation strategy and participant adherence, as manifest by changes in both costs and treatment effectiveness. Under a scenario of both reduced costs and 20% to 50% reduced effectiveness, the lifestyle intervention was cost-saving relative to the placebo intervention and the metformin intervention cost only $6600 to $21 000 per QALY.
Many recent studies have assessed the relative cost-effectiveness of interventions in diabetes. Few interventions in diabetes are cost-saving, that is, the experimental intervention is both more effective and less expensive than the comparator. Cost-saving interventions in diabetes include preconception counseling for women with type 1 diabetes (30
), angiotensin-converting enzyme inhibitor and angiotensin-receptor blocker therapy for patients with clinical nephropathy (31
), and intensive blood pressure control for patients with hypertension (33
). A recent report estimated that intensive glycemic control for patients with newly diagnosed type 2 diabetes costs approximately $41 000 per QALY over a lifetime (11
) and statin therapy in patients with type 2 diabetes, no coronary disease, and total cholesterol levels greater than 5.18 mmol/L (>200 mg/dL) costs approximately $52 000 per QALY (11
Cost-saving interventions present no difficulty with respect to policy implications. They should be rapidly and widely implemented since they are more effective and less expensive than existing therapies. However, most new treatments in diabetes are more effective and costly, requiring incremental resources per QALY. There is no universally accepted rule to evaluate such treatments (34
). Laupacis and colleagues (35
) have proposed a system to rate interventions on the basis of the likely magnitude of the net benefit associated with their application (cost per QALY). They argue that interventions that cost less than $20 000 per QALY are an appropriate way to use resources and those that cost $20 000 to $100 000 per QALY are probably appropriate, but those that cost greater than $100 000 per QALY may not be a good use of resources.
We based our model on the DPP. No simulation model can perfectly represent reality, and all models have inherent limitations (36
). Participants in the DPP, while broadly representative of the population with impaired glucose tolerance, were volunteers and may have been more highly motivated than nonparticipants. The DPP could not study all clinical relevant interventions or measure disease progression and intervention effects over a lifetime. When long-term information is not available, models may be used to integrate evidence from clinical trials to make inferences about future economic, quality of life, and health outcomes and to provide data for decision making. The predictions provided by a model depend on the clinical trial itself and the assumptions made in the simulation. In our base-case analyses, we assumed that the DPP interventions were applied as they were in the DPP for as long as an individual remained nondiabetic. We further assumed that the costs were the same as those in the DPP, the interventions would remain as effective as they were in the DPP, and participants developing diabetes would receive intensive therapy. Higher costs or lower effectiveness of interventions for diabetes prevention would tend to reduce the cost-effectiveness of diabetes prevention.
In summary, compared with the placebo intervention, the DPP lifestyle and metformin interventions provided substantial health benefits at an attractive cost. The lifestyle intervention, compared with the metformin intervention, provided greater health benefits at lower costs and, from the perspective of a fiscally prudent policymaker, represents the intervention of choice. Investment in DPP lifestyle and metformin interventions in high-risk individuals with impaired glucose tolerance may help stem the current epidemic of diabetes.