The DPS is a randomized, controlled, multicenter lifestyle intervention study conducted in Finland. The DPS included five study centers in Helsinki, Kuopio, Turku, Tampere, and Oulu. The main aim of the DPS was to assess the efficacy of lifestyle modification on preventing or delaying the onset of T2D in people with IGT. Study participants were recruited mainly by screening of high-risk individuals, such as first-degree relatives of T2D patients, who voluntarily responded to local advertisements, or were identified in earlier epidemiological surveys. The main inclusion criteria were BMI over 25 kg/m2, age 40–64 years, and IGT on the basis of the mean values of two oral glucose tolerance tests.
Randomization of the study participants started in November 1993, the recruitment period lasted until June 1998 and the intervention period lasted until the end of 2001. The data used in this work was based on the information of the study baseline and three-year
examinations. The study design and the methodology are described in more detail elsewhere (329-331).
The characteristics for the DPS population are presented in Table 13. Altogether 522 overweight individuals, 172 men and 350 women with IGT participated, and were randomly allocated to an intensive, individualized diet and exercise intervention or a control group. Randomization was done by the study physician, with the use of a randomization list, with stratification according to center, gender, and the mean plasma glucose concentration two hours after oral glucose challenge (331). Study design was single-blinded, as the staff members involved in the intervention had to be aware of the group assignment. Criteria for exclusion included the presence of chronic disease rendering survival for six years unlikely, and other characteristics (psychological or physical disabilities) deemed likely to interfere with participation in the study. The participants gave written informed consent. The study protocol was approved by the Ethics Committee of the National Public Health Institute in Helsinki, Finland.
9.2.2 Advice for the lifestyle intervention group
The main goals of the lifestyle intervention were based upon available evidence on risk factors of diabetes. The participants in the intervention group (n=265) were given detailed advice to achieve the goals: 1) weight reduction of ≥5%, 2) fat intake <30% of the total energy intake, 3) SFAs <10% of total energy intake, 4) dietary fiber intake to ≥15 g per 1000 kcal, and 5) moderate exercise for ≥30 minutes per day.
The intensive intervention consisted of seven face-to-face counseling sessions with the study nutritionist during the first year of the study, and one session every three months thereafter for three years. The first-year sessions were tailored based on the food records, focusing on specific individual problems. However, each session had a preplanned topic, for example regular meal patterns and substituting energy-dense foods containing SFAs, sugar, or alcohol with lower-energy items. Consumption of whole-grains instead of refined grains, abundant daily consumption of vegetables and fruits, consumption of low-fat milk and meat products, soft margarines and vegetable oils rich in unsaturated fatty acids were also recommended. The plate model was used to estimate portion sizes. Additionally, there were voluntary group sessions, expert lectures, low-fat cooking lessons, visits to local supermarkets, and possibility to have between-visit phone calls and discussions by letters.
The goal was to equip the participants with the necessary knowledge and skills and to achieve gradual, permanent behavioral changes (330). Very-low-calorie diet was considered to be used for two to five weeks, if preferred by the subject, to boost weight loss.
The exercise intervention was individualized and aimed at increasing all physical activity. It was based on daily physical activities, endurance exercise (such as walking, jogging, swimming, aerobic ball games, or skiing) and muscle strengthening. Progressive, individually tailored, supervised circuit-type resistance training sessions to improve the functional capacity and strength of the large muscle groups of the upper and lower body were also offered. Training sessions began four to six months after randomization. The exercise intervention has been described in more detail elsewhere (330,331).
9.2.3 Advice for the control group
At baseline, the participants in the control group (n=257) were given general verbal and written information, a two-page leaflet, on diet and exercise. This was done either individually or in one group session. The principles of the message for the control group were the same as for the intervention group participants: to reduce weight, increase physical activity, and to make qualitative changes in diet. The advice the control group received concerning healthy lifestyle could be regarded “a mini-intervention”. The control group visited the research centers once a year for three years and all the measurements were similar in both groups.
Table 13. The baseline characteristics of the participants in the Finnish DPS.1 DPS participants without BDI scores availablen=382 BDI-scores availablen=140 Intervention (n=196)Control (n=186)P-value2Intervention (n=69)Control (n=71)P-value2 Men/women63/13350/1360.26028/4131/400.422 Age (years) 54.7 (7.5)53.9 (6.9)0.33357.7 (6.4)57.4 (6.5)0.786 Education: high school or upper (%) 37 33 0.23622 31 0.566 Living without a spouse (%) 26 23 0.55422 15 0.756 BDI scores (points)6.8 (5.6)6.7 (5.5)0.945 BDI scores ≥11 (n/%)14/2016/230.453 Antidepressant medicine use (n)540.533120.511 Body mass index (kg/m2)31.8 (4.8)31.0 (4.4)0.11130.2 (3.4)31.2 (4.7)0.166 Physical activity (min/week) 375 (319)410 (378)0.335535 (353)507 (390)0.663 Total energy (kcal/day) 1780 (527)1737 (532)0.4321744 (503)1760 (515)0.857 Fat (% of energy) 36.4 (6.9) 37.2 (6.2) 0.20235.2 (6.3) 36.8 (7.2) 0.147 PUFAs (% of energy) 5.85 (1.73)5.94 (2.26)0.6335.33 (1.66)5.58 (1.32)0.408 Fiber (g/day) 20.0 (7.3) 19.3 (7.7) 0.38121.1(6.9) 20.4 (7.0) 0.805 Alcohol (g/day) 8.9 (17.8)6.1 (12.9)0.0805.1 (16.4)4.8 (9.4) 0.885 Smoking (ever smokers %)41450.27244550.118 Abbreviations: BDI, Beck Depression Inventory; DPS, Diabetes Prevention Study; PUFA, polyunsaturated fatty acid 1Data are expressed as the mean (SD) unless otherwise indicated. 2Significance of the difference between groups was assessed by Student’s t test, Mann-WhitneyU-test and χ2 test.
9.2.4 Assessment of depressive symptoms
Depressive symptoms were assessed with the Finnish version of the self-administered 21-item BDI, which is one of the most commonly used instruments for measuring the severity of depression (42). The BDI is a well-known and well-validated self-report measurement method of depressive symptoms (332). Also the Finnish version of the 21-BDI has been validated (333). The version used in the DPS, BDI Ia (Appendix 1), is a modestly modified version of the original version, as for example the alternative “a” and “b” statements have been removed to ease the use, and symptoms are asked for the preceding two weeks (334).
However, the symptom evaluation scale is similar to the previous version. In clinical work, the BDI has been established as a common tool for assessing depressive symptoms and progress in the follow-up. Moreover, the mean BDI scores correlate well with the prevalence of depression determined by clinical interviews (335).
Patients choose from a group of sentences the one which best describes how they have been feeling during the past two weeks, resulting in total scores from 0 to 63. The cut-off point for elevated depressive symptoms was set at 11 points, 0 to 10 indicating normal mood and 11 or more indicating elevated depressive symptoms. The same cut-off point was used in an earlier intervention study (303). Participants reported the use of antidepressant medication at baseline and subsequently at each annual study visit. There were two study centers out of five that carried out the BDI, and therefore the BDI scores were available for 140 individuals (69 in the intervention group and 71 in the control group; 59 men and 81 women, respectively). Table 13 presents the baseline characteristics for those participants who had BDI scores available, as well as for the rest of the study population. There were no statistically significant differences in any of the variables between intervention and control groups.
9.2.5 Assessment of diet and other variables
Diet was assessed using three-day food records four times a year. Intakes of nutrients were calculated using a dietary analysis program, the Finnish Food Composition Database (Fineli), developed by the National Public Health Institute (336). The program allows modification of database recipes, e.g., the use of skimmed instead of whole milk can be coded (330). Participants completed a medical-history questionnaire and underwent a physical examination. Participants underwent a 75-g oral glucose tolerance test at baseline and at each annual visit, as described previously (329,331). Physical activity was assessed at baseline and at each annual visit with the validated the 12-month Leisure-time Physical Activity Questionnaire (325). Information on antidepressant prescriptions was obtained from a linkage to the medication reimbursement register of the Finnish Social Insurance Institution. The weight and height of the participants was measured by a study nurse, and the BMI was calculated as the ratio of weight in kilograms to the square of height in meters.
Anthropometric measurements of height, weight, waist circumference and blood pressure measurements have been described in more detail previously (329). Weight was measured at every visit, and a weight chart was drawn.
9.2.6 Statistical methods
The data were expressed as means ± standard deviations (SD). The α–level was set at ≤0.05.
The differences in baseline variables between intervention and control group were tested by using the ANOVA, Student’s t-test, Mann-Whitney U-test and chi-squared test. Normal distributions were tested with the Kolmogorov-Smirnov (Lilliefors) test. The non-parametric Mann-Whitney U-test was utilized when the distribution of the values was skewed. Non-parametric two-related samples test (Wilcoxon) was used to evaluate the changes in BDI scores within the intervention and control groups during the intervention.
Because the BDI scores had skewed distributions, unadjusted differences in mean BDI scores between groups were evaluated using Mann-Whitney U-tests both at baseline and at
three years. A forward stepwise linear multivariate regression analysis was used to find the strongest determinants of the change in BDI scores (P in 0.10, P out 0.20). All statistical tests were two-tailed. Data were analyzed using SPSS for Windows version 14.0 statistical software (SPSS Inc., Chicago, Illinois, U.S.).