Economic Evaluation of Combined Diet and Physical Activity Promotion Programs to Prevent Type 2 Diabetes Among Persons at Increased Risk: A Systematic Review for the Community Preventive Services Task Force

Diabetes is a highly prevalent, severe, and costly disease in the United States. Approximately 29 million Americans (9.3% of the U.S. population) had diabetes in 2012, and that number is projected to increase (1, 2). Diabetes is the leading cause of kidney failure, blindness, and amputation, as well as a major cause of heart disease and stroke (2). In the United States in 2012, the total medical cost of diagnosed diabetes was estimated at $176 billion, and the cost of productivity loss due to diabetes was another $69 billion (3).

Type 2 diabetes accounts for 90% to 95% of all cases of diagnosed diabetes. Common risk factors for type 2 diabetes include obesity, family history of diabetes, physical inactivity, hypertension, hypercholesterolemia, and elevated glucose level. In addition, approximately 37% of the U.S. population aged 20 years or older and 51% of those aged 65 years or older had prediabetes in 2012, meaning that they were at increased risk for type 2 diabetes (2). However, only about 10% of at-risk persons knew their risk status (4).

Randomized clinical trials around the world have shown that combined diet and physical activity promotion programs could prevent or delay progression to type 2 diabetes among persons at increased risk (5–8). Studies have also demonstrated the feasibility and effectiveness of such programs when they are implemented in primary care or community settings (9). In 2014, a systematic review done for the Community Preventive Services Task Force found that programs implemented in health care or community settings effectively reduced the risk for diabetes in persons at increased risk; increased the likelihood of reversion to normoglycemia; and reduced weight and other risk factors for cardiovascular disease, such as elevated blood pressure and lipid levels (10).

Given the potentially large population that is eligible for diet and physical activity promotion programs and the resources needed for implementation, information on program cost and cost-effectiveness is critical for policy decisions, such as benefit coverage for payers, as well as planning for program design and implementation. As a companion to the aforementioned effectiveness review, we did this systematic economic review for the Community Preventive Services Task Force to estimate the cost associated with diet and physical activity promotion programs and the cost-effectiveness and cost–benefit ratios of these programs.

Methods

Data Sources and Searches

We searched the Cochrane Library, EMBASE, MEDLINE, PsycINFO, Sociological Abstracts, Web of Science, EconLit, and CINAHL for English-language articles published between January 1985 and 7 April 2015. Details of the search strategy are available on the Guide to Community Preventive Services (Community Guide) Web site (www.thecommunityguide.org) and in Appendix Table 1 (11). We also screened reference lists of relevant studies and reviews and considered studies identified by the parallel review of the effectiveness of diet and physical activity promotion programs (10).

Study Selection

We included studies that provided information on program cost; cost–benefit ratio; or incremental cost-effectiveness ratio (ICER), which is measured as dollars per life-year gained (LYG), quality-adjusted life-year (QALY) saved, or disability-adjusted life-year (DALY) averted. Included studies on program cost had to evaluate the actual program implementation cost. Included cost-effectiveness or cost–benefit studies had to meet published criteria for conducting and reporting economic evaluation analysis (12).

We used the same inclusion criteria as the aforementioned effectiveness review for study population, intervention, comparison population, and publication language (10). Criteria included a population at increased risk for type 2 diabetes, based on glycemic measures or risk scores for diabetes, presence of cardiovascular disease, or presence of the metabolic syndrome; intervention with both diet and physical activity components delivered in at least 2 contact sessions over at least 3 months; comparison with a similar population receiving either usual care (standard lifestyle advice) or no intervention for the cost-effectiveness studies; and publication in English. We further restricted our review to studies in high-income countries to provide economic estimates relevant to U.S. settings and populations.

Data Extraction and Quality Assessment

Two authors extracted data from each article according to the Cochrane systematic review protocol (13) and the Community Guide protocol for economic evaluations (14).

Data Synthesis and Analysis

Intervention costs are reported as program costs per participant, including costs to identify eligible participants (through recruitment in the community, referral from providers, or screening and referral in study settings) and to implement the diet and physical activity promotion program (staff time, training materials, and other costs). We also generated program costs per participant per session, calculated by dividing program costs per participant by the total number of core and maintenance sessions delivered. Medians and interquartile intervals (IQIs) of study estimates were reported as summary measures. If there were 4 data points, we reported the range; if there were 3 or fewer data points, all were reported.

Subgroup analyses of intervention costs were done to explore potential factors affecting costs. For delivery setting, we grouped each study into those based on the U.S. DPP (Diabetes Prevention Program) study, in which the intervention was delivered in a clinical trial setting following rigorous procedures as described in study protocols (5), and those done in real-world settings, in which diet and physical activity promotion programs were translated to community or primary care settings, with (translational DPP programs) or without (translational non-DPP programs) explicit adaptation of DPP training materials.

For delivery method, we categorized each study into 1 of the following groups: individual-based programs, in which a participant met 1-on-1 with the program provider at each core session; group-based programs, in which the participants met as a group with the program provider at each core session; or mixed programs, in which the core sessions included both individual and group sessions.

For the type of personnel delivering the program, we grouped each study by whether the program was delivered by health professionals (such as medical staff, physicians, nurses, physiotherapists, case managers, or dietitians), trained laypersons (such as certified diabetes educators, lay health educators, trained community health workers, or trained volunteers with type 2 diabetes), or a mix of health professionals and trained laypersons.

Cost-effectiveness estimates were measured as ICERs, with medians and IQIs provided as summary measures. To improve comparability of ICERs across the studies, we reported them separately by the outcome measures used in different studies: QALYs saved, LYGs, or DALYs averted. For studies found to be cost-saving, we calculated the negative net cost per QALY saved, LYG, or DALY averted whenever possible to calculate the median ICER.

Two economic perspectives were considered: the health system perspective, in which only medical costs and benefits relevant to health systems were considered, and the societal perspective, in which direct nonmedical and indirect costs were also considered. When studies provided sufficient data, we calculated ICERs for perspectives beyond those reported.

As with cost estimates, subgroup analysis of ICERs was done by delivery method. We examined cost-effectiveness estimates by type of analysis: within-trial analysis, in which ICERs were calculated from data on actual costs and benefits; modeling of a trial or extension of trials, in which studies used simulation models to estimate program cost and effectiveness during or beyond the trial period; or modeling of the national effect, in which studies estimated ICERs for programs delivered by scaling up programs to the entire country in which the study was conducted.

Because time horizon is important in program planning and budget allocation, we reported ICERs by length of follow-up (short-term [<10 years] or long-term [≥10 years]). In addition, we reported ICERs stratified by country setting (U.S.- or non–U.S.-based) to better inform programs in the United States.

All costs were adjusted to 2013 U.S. dollars by using the Consumer Price Index for medical care services (15) and annual foreign exchange rates from the Federal Reserve Bank for conversion of other currencies (16). If a study did not mention the year used in cost calculations, we assumed costs to be as of 1 year before the study publication year. Interventions were considered cost-effective if the ICER was less than $50 000 per QALY saved, less than $50 000 per LYG (17), or less than the per capita gross domestic product of the relevant country for cost per DALY averted, as recommended by the World Health Organization (18).

Role of the Funding Source

This study was done by employees of the U.S. government as part of their official duties and received no external funding.

Results

After screening, 28 studies met our inclusion criteria and were included in our final review (Figure 1) (19–46). Of these, 6 cost-only studies (20–23, 26, 27) and 6 cost-effectiveness studies (19, 24, 25, 28–30) provided information on the actual cost of diet and physical activity promotion programs, and 22 contributed cost-effectiveness estimates of the programs (19, 24, 25, 28–46). Fourteen studies were U.S.-based (19–24, 26, 27, 31, 35–38, 46). No cost–benefit studies were identified.

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Intervention Costs

Of the 12 studies that reported the actual costs of implementing the program (20–31), only 4 included costs for identifying persons at increased risk (22, 24, 27, 29). The major cost driver was staff time to deliver the intervention. Most studies provided program cost information embedded in an evaluation of program effectiveness or cost-effectiveness without doing a formal cost analysis (Appendix Table 2).

Program costs per participant ranged from $191 to $5881 (median, $653 [IQI, $383 to $1160]). The most expensive program was the 10-year DPP/DPPOS (Diabetes Prevention Program Outcomes Study), which cost $5881 per participant (19). The cost from the first 3 years (the trial period for DPP, which was based on individual sessions delivered by health professionals) was $4687; the remaining maintenance and follow-up period, called the DPPOS period, was group-based and accounted for only $1194. The translational programs were less intense than the DPP trial and usually had fewer sessions and shorter duration. Most of them were group-based or had a mixture of group and individual sessions and were delivered by either trained laypersons or a mix of health professionals and trained laypersons (Appendix Table 2). They were also less costly than the DPP trial. The median program cost per participant was $424 (IQI, $340 to $793) for the 8 translational DPP programs (20–27) and $1160 (range, $427 to $1416; 4 data points) for the 3 translational non-DPP programs (28–30) (Table 1).

The median cost per participant per session was $30. The cost per session of the DPP/DPPOS was $102. The median costs per participant per session for the 8 translational DPP programs and the 3 translational non-DPP programs were $25 (IQI, $16 to $48) and $27 (range, $4 to $64), respectively (Table 1).

The median cost per participant was lower in the group-based programs ($417 [IQI, $341 to $600]) (20–25, 28, 29) than in the DPP/DPPOS ($5881) (19) and the translational non-DPP program ($1242) (29) (Appendix Table 2), both of which used individual sessions. It was also lower than the median cost of programs with a mix of individual and group sessions (median, $918 [range, $839 to $1416]) (26, 27, 30) (Table 1). The median cost per participant for translational programs delivered by trained laypersons (median, $357 [range, $191 to $839]) (21, 22, 26) was lower than that for those delivered by health professionals (median, $1077 [IQI, $381 to $1329]; 4 programs; 5 data points) (20, 28–30); however, there was large variation within personnel type, possibly due to a mixture of delivery settings and methods (Table 1).

Cost-Effectiveness of the Programs

Of 22 studies reporting the cost-effectiveness of the programs, 8 were U.S.-based (19, 24, 31, 35–38, 46). Seventeen studies reported the outcome measure as cost per QALY saved (19, 24, 25, 28–31, 35–40, 42–44, 46), 6 reported cost per LYG (32–34, 39, 40, 43), and 2 reported cost per DALY averted (41, 45). All studies except 1 (42) reported ICERs from a health system perspective. Eight studies (19, 28, 31, 36, 38, 39, 42, 44) reported ICERs from a societal perspective, and 7 (19, 28, 31, 36, 38, 39, 44) reported both health system and societal perspectives. However, only 1 study included all of the costs and benefits from society as a whole (44). Eighteen studies used modeling techniques (24, 28, 30, 32–46), 2 of which modeled the cost-effectiveness of nationwide community-based programs (45, 46). Fourteen studies were based on data from the DPP trial or the Finnish Diabetes Prevention Study, which used individual sessions (19, 31, 33–41, 43, 44, 46). Most modeling studies considered the health and cost consequences of the program for at least 10 years (28, 30, 32–43, 45, 46). Appendix Table 3 provides estimates of cost-effectiveness or cost–utility ratios from individual studies, which served as the basis for the summary measure of ICERs.

Of the 16 studies that included cost per QALY saved from the health system perspective, all but 1 (35) reported ICERs below the cost-effectiveness threshold of $50 000 per QALY saved (Figure 2). Three studies reported cost savings (36, 43, 46). The median ICER from the 16 studies was $13 761 per QALY saved (IQI, $3067 to $21 899).

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From the health system perspective, subgroup analyses were done with 5 studies that reported ICERs for both individual- and group-based programs (19, 31, 35, 36, 38). The medians were $15 846 (IQI, $7980 to $72 723) and $1819 (IQI, −$5027 to $16 443) per QALY, respectively. Six studies (24, 25, 28–30, 46) that evaluated the cost-effectiveness of translational programs found a median ICER of $7115 per QALY (IQI, $2252 to $27 582). Two of them were conducted in the United States (24, 46); 1 reported an ICER of $5494 per QALY, and the other reported cost savings.

Studies in the United States reported a median ICER of $9824 per QALY (IQI, $1930 to $41 982; 8 studies), and non-U.S. studies reported a median ICER of $13 860 per QALY (IQI, $6203 to $21 899; 8 studies). By method, the median ICER of the 4 within-trial analyses was $28 097 per QALY (range, $5359 to $50 694) (19, 25, 29, 31). Twelve modeling studies reported a median ICER of $13 367 per QALY (IQI, $2303 to $17 614). By time horizon, the median ICERs were $17 614 per QALY (IQI, $5427 to $45 521; 5 studies) for studies that considered the benefits and costs of the program over less than 10 years and $13 367 per QALY (IQI, $1805 to $15 846; 11 studies) for studies that extended 10 years or beyond (Table 2).

Two studies conducted in Australia (41, 45) reported cost per DALY averted from the health system perspective and used the Australian 2013 per capita gross domestic product of $67 468 as the cost-effectiveness threshold (47). Both studies found the programs to be cost-effective ($21 195 and $50 707 per DALY).

Six other studies reported ICERs as cost per LYG (32–34, 39, 40, 43); all were below the $50 000 threshold. Two studies showed negative costs per LYG, which indicated cost savings (34, 43). The median ICER was $2684 per LYG (IQI, −$2444 to $17 410).

Discussion

Our review found a median ICER for diet and physical activity promotion programs of $13 761 per QALY saved. The 25th and 75th percentiles of the ICERs from the 16 studies that reported cost per QALY saved from the health system perspective were both under $50 000 per QALY, which is a conventional cost-effectiveness threshold (17). The ICERs of diet and physical activity promotion programs measured by cost per LYG or DALY averted were also all under commonly used cost-effectiveness thresholds (18). Thus, we conclude that diet and physical activity promotion programs are cost-effective and involve an efficient use of health care resources.

Our evidence search identified 4 pertinent systematic or narrative reviews evaluating the evidence on cost-effectiveness of diet and physical activity promotion programs for participants at increased risk for type 2 diabetes (48–51). Results from these reviews also suggested that such programs were either cost-effective or cost-saving, independent of country or delivery setting. Previous reviews did not synthesize evidence on costs of diet and physical activity promotion programs. Our systematic review includes 18 additional studies; supports the overall finding of cost-effectiveness; and provides comparative economic estimates by delivery method, setting, and staffing to inform program planning and implementation.

Given the current evidence base, we cannot definitively conclude that the programs are cost-saving. Only 3 studies that reported cost per QALY saved found the program to be cost-saving (36, 43, 46). For the 2 U.S. studies, 1 (36) reported that the DPP program was cost-saving over a lifetime horizon when delivered in group sessions, and the other (46) reported that a nationwide diabetes prevention program became cost-saving in its 11th year, implying that the programs may not save costs in the short term. However, few health care interventions have been found to be cost-saving, and many medical services that are typically covered by insurance have much higher ICERs than the diet and physical activity promotion programs (52). In a 2010 review of the cost-effectiveness of interventions for diabetes prevention and control, the median ICER for lifestyle interventions was at the low end of the spectrum, and the interventions were much more cost-effective than many diabetes treatment interventions, such as intensive glycemic control (48).

Most cost-effectiveness studies in our review were model-based because most trials lasted 3 years or less, but both the health and economic effects of the program were expected to last beyond the trial period. Estimated long-term ICERs of the programs from those modeling studies provided valuable information for decision makers in forecasting the health and economic effects of the program. One common critique of model-based studies is a lack of transparency of the models. To ensure the validity of the estimates, we explicitly abstracted studies in which information on program cost and effectiveness was clearly described in the model. Most studies used either a previously validated model or a model used in previous peer-reviewed publications, and all studies explicitly stated important assumptions used to predict future health and economic outcomes of the program. Model-based ICER estimates varied widely, which could have been due to different model structures and health assumptions, such as the rates of progression of diabetes and its complications beyond the trial period. Despite this variation in the derivation of ICERs with the use of modeling, all but 1 study showed that the ICERs of the programs were far below conventional cost-effectiveness thresholds. The 1 study that reported a much higher ICER used a model with a structure that differed greatly from the other studies and assumed a much slower rate of progression to diabetes in the model (35). However, even for this study, when the intervention was delivered in a group setting, the ICER was below the threshold of $50 000 per QALY.

Our findings have several important implications for programs implemented in the field, such as the National Diabetes Prevention Program, a public–private partnership led by the Centers for Disease Control and Prevention to implement a low-cost intervention adapted from the DPP in communities across the country (53). Group-based programs were less costly and more cost-effective than individual-based programs. In group-based programs, several participants could be counseled in the same session; thus, the cost per participant was lower. Evidence also showed that group-based programs may achieve effectiveness similar to that for individual-based programs (10). To reduce cost and achieve higher cost-effectiveness of diet and physical activity promotion programs, it seems that group-based programs should be used when the programs are implemented in real-world settings.

The cost of these programs may present a barrier to implementation despite the evidence on program cost-effectiveness. The original DPP trial was individual-based and resource-intensive. However, the program cost was much lower when it was implemented in a group format in primary care clinics and communities or translational DPP programs and was lower than or similar to currently reimbursable medical practices. For example, the annual per capita expenditure (in 2012 U.S. dollars) on prescription medications for persons with diabetes was $1423 (3), and Medicare currently pays $25.52 per counseling session for weight-loss programs (54). Further, program scale-up is expected to create economies of scale, further reducing the cost. Programs were found to be more cost-effective in longer-term follow-up studies, given that health benefits often last beyond the program period. In addition, many diabetes-related complications do not appear immediately after a person develops diabetes, which limits the ability of short-term studies to capture the full range of health benefits and medical costs avoided by the intervention.

We identified several limitations of the evidence base that future research should address. First, few studies estimated the cost associated with recruiting and engaging eligible persons to participate in the programs, which may generate additional costs when the programs are scaled up. Second, only 2 studies provided a rigorous cost analysis, and there is a lack of information to better understand the cost of scaling up the programs, such as the cost of programs delivered by trained laypersons (27). Third, only 2 studies evaluated the cost-effectiveness of programs implemented in primary care and community settings in the United States. Fourth, although the societal perspective is often preferred, of the 22 cost-effectiveness studies identified, only 8 reported this perspective and only 1 included all cost and benefit components (12). In addition, 1 study reported an ICER from a health plan (payer) perspective. Fifth, no cost–benefit analyses were identified in the review. Finally, although we attempted to stratify ICERs by program features, these characteristics were so intertwined that formal statistical testing of the effect of a single feature was not feasible.

In summary, the available economic evidence indicates that combined diet and physical activity promotion programs are cost-effective when delivered to persons at increased risk for type 2 diabetes. Evidence further suggests that programs using group sessions delivered by trained diabetes educators or laypersons are an economically efficient approach for communities and health care systems, especially those faced with limited resources and an increasing demand for services.

Health care providers have an essential role in the prevention of type 2 diabetes among patients at increased risk. In most cases, clinicians will be involved in identifying at-risk patients, delivering initial or ongoing behavioral counseling (55), and arranging referrals to available services. Our findings, combined with the findings from the concurrent effectiveness review (10), add to the growing body of evidence that diet and physical activity promotion programs using group sessions delivered by trained personnel are both effective and cost-effective. As national, state, and local efforts to implement evidence-based programs expand, health care providers will have additional, effective intervention options for patients identified as being at increased risk for type 2 diabetes.