Given the prevalence of diabetes and the personal and economic burden it imposes, efforts have been made to identify the best ways of preventing type 2 diabetes or delaying its onset. Initially, this consisted of randomized clinical trials, followed by translational interventions in the community. As individuals with prediabetes and the metabolic syndrome are at elevated risk for more serious conditions, including diabetes and cardiovascular disease, prevention efforts typically focus on the reduction of diabetes risk factors. One approach is the use of behavioral lifestyle programs, including those adapted from the Diabetes Prevention Program (DPP) lifestyle intervention [13,14]. The focus of these programs is weight loss, a reduction of fat in the diet, and increased physical activity.
2.7.1 Clinical Trials for the Prevention of Type 2 Diabetes
The first major study investigating the possibility of diabetes prevention through lifestyle intervention was the Swedish Malmö study [109]. Enrolling 181 individuals with impaired glucose tolerance (IGT), the study protocol included a six-month period of supervised physical training and six months of dietary education. In 1991, six-year follow-up results were published, indicating that it was possible to induce and maintain lifestyle changes in those with IGT, resulting in improvement in glucose tolerance as well as reducing blood pressure and lipids.
Other international studies also demonstrated that lifestyle modification is an effective approach to prevent or delay diabetes. Results from the Da Qing study in China showed that participants with IGT randomized to one of three active treatment groups, consisting of diet only, exercise only, or diet plus exercise, had diabetes risk reductions of 31%, 46%, and 42%,
respectively, when compared with the control group [16]. The Finnish Diabetes Prevention Study (DPS) reported in 2001 that among participants with IGT, the risk of type 2 diabetes was reduced by 58% in the lifestyle intervention group, compared to the control group [15]. Follow-up of DPS participants over 13 years shows a continuing reduction in diabetes risk in the intervention group, when compared to the control group [110].
In 2002, results from the Diabetes Prevention Program (DPP) in the US were published.
In this trial, 3,234 participants without diabetes were randomized to one of three study arms:
placebo, metformin (850 mg, 2 times per day), or lifestyle modification, with minimum goals of 150 minutes per week of moderate physical activity and 7% weight loss. After almost three years of follow-up, the lifestyle and metformin groups were found to have diabetes risk reductions of 58% and 31% respectively, relative to the placebo group [13]. As well as reducing the incidence of type 2 diabetes, the DPP lifestyle participants had a 41% reduction in the incidence of the metabolic syndrome, compared with the placebo [14]. The DPP lifestyle intervention was also more effective than the placebo or metformin in reducing cardiovascular risk factors and the need for pharmacologic therapy to achieve target blood chemistry values [111]. Ongoing follow-up of DPP participants as part of the Diabetes Prevention Program Outcomes Study (DPPOS) confirms that participants in the lifestyle arm of the original DPP intervention continue to benefit despite partial weight regain, with diabetes incidence rates among lifestyle participants 34% lower in the lifestyle group, and 18% lower in the metformin group, compared with the placebo after 10 years [112]. These DPP results, in conjunction with the earlier international findings, have established the clinical efficacy of type 2 diabetes prevention based on moderate lifestyle intervention.
Building on the studies described above, the Indian Diabetes Prevention Programme [113] randomized individuals of Asian Indian background into one of four groups: 1. Control; 2.
Lifestyle modification; 3. Metformin; 4. Lifestyle plus metformin. The participants had IGT at baseline and were younger, less overweight, and more insulin resistant than the previously mentioned investigations. Lifestyle modification consisted of advice on a healthy diet, specifically, a reduction in total calories, refined carbohydrates, and fats, as well as the avoidance of sugar and inclusion of fiber rich foods. After a median follow period of 30 months, the risk of diabetes was reduced by 28.5% (p=0.018) in the lifestyle group and 26.4% (p=0.029) in the metformin group, compared to the controls. The combination of metformin and lifestyle conferred no additional risk reduction beyond the components taken separately.
2.7.2 Translational Research Studies
Since publication of the DPP results, research efforts have focused on translating the clinical findings of the DPP in a variety of settings. Typically, the DPP curriculum is adapted for group presentation, rather than the one-on-one delivery used in the DPP, and the content of the original 16 sessions may be condensed and offered in fewer sessions.
Several groups have developed DPP-based curriculums and approaches. Of particular interest is the Group Lifestyle Balance (GLB) program, developed by the Diabetes Prevention Support Center (DPSC) at the University of Pittsburgh and used in this investigation. The GLB program consists of 12 weekly core group sessions, with bi-weekly and then monthly follow-up sessions. This year-long program is designed to be delivered by trained group leaders who have
settings, including a primary care practice, out-patient diabetes education clinics, fitness centers, a church, and an underserved urban community [17-25,33]. A DVD adaptation of the GLB program has also been shown to be effective [24]. Other translational approaches include the use of supervised lay community health workers as group leaders in order to increase the pool of potential leaders [44-46,50,114], and various electronic media approaches [48,49,115].
2.7.3 The National Diabetes Prevention Program
Building on the success of clinical and translational programs for preventing type 2 diabetes, in 2010 the US Congress authorized the establishment of the National Diabetes Prevention Program (National DPP) by the Centers for Disease Control (CDC) in order to increase the availability of low cost diabetes prevention intervention programs [116]. This program focuses on four core elements: training, recognition programs, intervention sites, and health marketing.
A variety of training programs are currently available, including through the Diabetes Prevention Support Center (DPSC) at the University of Pittsburgh and the Diabetes Training and Technical Assistance Center (DTTAC) at Emory University. The Diabetes Prevention Recognition Program (DPRP) is a key component of the National DPP. The DPRP maintains a record of and grants recognition to programs that have demonstrated an ability to effectively deliver the lifestyle change intervention and ensure quality and consistency, using an approved curriculum. Additionally, through recognized delivery sites, the National DPP facilitates the provision of diabetes prevention programming in sites around the country, and is helping to facilitate strategies and approaches to increase referrals and participation in these programs [116].
3.0 HEALTH-RELATED QUALITY OF LIFE IN CHRONIC