Metformin for people with impaired glucose tolerance or impaired fasting blood glucose

Metformin for prevention or delay of type 2 diabetes mellitus and its associated complications in persons at increased risk for the development of type 2 diabetes mellitus

BACKGROUND

The projected rise in the incidence of type 2 diabetes mellitus (T2DM) could develop into a substantial health problem worldwide. Whether metformin can prevent or delay T2DM and its complications in people with increased risk of developing T2DM is unknown.

OBJECTIVES

To assess the effects of metformin for the prevention or delay of T2DM and its associated complications in persons at increased risk for the T2DM.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Scopus, ClinicalTrials.gov, the World Health Organization (WHO) International Clinical Trials Registry Platform and the reference lists of systematic reviews, articles and health technology assessment reports. We asked investigators of the included trials for information about additional trials. The date of the last search of all databases was March 2019.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) with a duration of one year or more comparing metformin with any pharmacological glucose-lowering intervention, behaviour-changing intervention, placebo or standard care in people with impaired glucose tolerance, impaired fasting glucose, moderately elevated glycosylated haemoglobin A1c (HbA1c) or combinations of these.

DATA COLLECTION AND ANALYSIS

Two review authors read all abstracts and full-text articles and records, assessed risk of bias and extracted outcome data independently. We used a random-effects model to perform meta-analysis and calculated risk ratios (RRs) for dichotomous outcomes and mean differences (MDs) for continuous outcomes, using 95% confidence intervals (CIs) for effect estimates. We assessed the certainty of the evidence using GRADE.

MAIN RESULTS

We included 20 RCTs randomising 6774 participants. One trial contributed 48% of all participants. The duration of intervention in the trials varied from one to five years. We judged none of the trials to be at low risk of bias in all 'Risk of bias' domains. Our main outcome measures were all-cause mortality, incidence of T2DM, serious adverse events (SAEs), cardiovascular mortality, non-fatal myocardial infarction or stroke, health-related quality of life and socioeconomic effects.The following comparisons mostly reported only a fraction of our main outcome set. Fifteen RCTs compared metformin with diet and exercise with or without placebo: all-cause mortality was 7/1353 versus 7/1480 (RR 1.11, 95% CI 0.41 to 3.01; P = 0.83; 2833 participants, 5 trials; very low-quality evidence); incidence of T2DM was 324/1751 versus 529/1881 participants (RR 0.50, 95% CI 0.38 to 0.65; P < 0.001; 3632 participants, 12 trials; moderate-quality evidence); the reporting of SAEs was insufficient and diverse and meta-analysis could not be performed (reported numbers were 4/118 versus 2/191; 309 participants; 4 trials; very low-quality evidence); cardiovascular mortality was 1/1073 versus 4/1082 (2416 participants; 2 trials; very low-quality evidence). One trial reported no clear difference in health-related quality of life after 3.2 years of follow-up (very low-quality evidence). Two trials estimated the direct medical costs (DMC) per participant for metformin varying from $220 to $1177 versus $61 to $184 in the comparator group (2416 participants; 2 trials; low-quality evidence). Eight RCTs compared metformin with intensive diet and exercise: all-cause mortality was 7/1278 versus 4/1272 (RR 1.61, 95% CI 0.50 to 5.23; P = 0.43; 2550 participants, 4 trials; very low-quality evidence); incidence of T2DM was 304/1455 versus 251/1505 (RR 0.80, 95% CI 0.47 to 1.37; P = 0.42; 2960 participants, 7 trials; moderate-quality evidence); the reporting of SAEs was sparse and meta-analysis could not be performed (one trial reported 1/44 in the metformin group versus 0/36 in the intensive exercise and diet group with SAEs). One trial reported that 1/1073 participants in the metformin group compared with 2/1079 participants in the comparator group died from cardiovascular causes. One trial reported that no participant died due to cardiovascular causes (very low-quality evidence). Two trials estimated the DMC per participant for metformin varying from $220 to $1177 versus $225 to $3628 in the comparator group (2400 participants; 2 trials; very low-quality evidence). Three RCTs compared metformin with acarbose: all-cause mortality was 1/44 versus 0/45 (89 participants; 1 trial; very low-quality evidence); incidence of T2DM was 12/147 versus 7/148 (RR 1.72, 95% CI 0.72 to 4.14; P = 0.22; 295 participants; 3 trials; low-quality evidence); SAEs were 1/51 versus 2/50 (101 participants; 1 trial; very low-quality evidence). Three RCTs compared metformin with thiazolidinediones: incidence of T2DM was 9/161 versus 9/159 (RR 0.99, 95% CI 0.41 to 2.40; P = 0.98; 320 participants; 3 trials; low-quality evidence). SAEs were 3/45 versus 0/41 (86 participants; 1 trial; very low-quality evidence). Three RCTs compared metformin plus intensive diet and exercise with identical intensive diet and exercise: all-cause mortality was 1/121 versus 1/120 participants (450 participants; 2 trials; very low-quality evidence); incidence of T2DM was 48/166 versus 53/166 (RR 0.55, 95% CI 0.10 to 2.92; P = 0.49; 332 participants; 2 trials; very low-quality evidence). One trial estimated the DMC of metformin plus intensive diet and exercise to be $270 per participant compared with $225 in the comparator group (94 participants; 1 trial; very-low quality evidence). One trial in 45 participants compared metformin with a sulphonylurea. The trial reported no patient-important outcomes. For all comparisons there were no data on non-fatal myocardial infarction, non-fatal stroke or microvascular complications. We identified 11 ongoing trials which potentially could provide data of interest for this review. These trials will add a total of 17,853 participants in future updates of this review.

AUTHORS' CONCLUSIONS

Metformin compared with placebo or diet and exercise reduced or delayed the risk of T2DM in people at increased risk for the development of T2DM (moderate-quality evidence). However, metformin compared to intensive diet and exercise did not reduce or delay the risk of T2DM (moderate-quality evidence). Likewise, the combination of metformin and intensive diet and exercise compared to intensive diet and exercise only neither showed an advantage or disadvantage regarding the development of T2DM (very low-quality evidence). Data on patient-important outcomes such as mortality, macrovascular and microvascular diabetic complications and health-related quality of life were sparse or missing.

Diet, physical activity or both for prevention or delay of type 2 diabetes mellitus and its associated complications in people at increased risk of developing type 2 diabetes mellitus

BACKGROUND

The projected rise in the incidence of type 2 diabetes mellitus (T2DM) could develop into a substantial health problem worldwide. Whether diet, physical activity or both can prevent or delay T2DM and its associated complications in at-risk people is unknown.

OBJECTIVES

To assess the effects of diet, physical activity or both on the prevention or delay of T2DM and its associated complications in people at increased risk of developing T2DM.

SEARCH METHODS

This is an update of the Cochrane Review published in 2008. We searched the CENTRAL, MEDLINE, Embase, ClinicalTrials.gov, ICTRP Search Portal and reference lists of systematic reviews, articles and health technology assessment reports. The date of the last search of all databases was January 2017. We continuously used a MEDLINE email alert service to identify newly published studies using the same search strategy as described for MEDLINE up to September 2017.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) with a duration of two years or more.

DATA COLLECTION AND ANALYSIS

We used standard Cochrane methodology for data collection and analysis. We assessed the overall quality of the evidence using GRADE.

MAIN RESULTS

We included 12 RCTs randomising 5238 people. One trial contributed 41% of all participants. The duration of the interventions varied from two to six years. We judged none of the included trials at low risk of bias for all 'Risk of bias' domains.Eleven trials compared diet plus physical activity with standard or no treatment. Nine RCTs included participants with impaired glucose tolerance (IGT), one RCT included participants with IGT, impaired fasting blood glucose (IFG) or both, and one RCT included people with fasting glucose levels between 5.3 to 6.9 mmol/L. A total of 12 deaths occurred in 2049 participants in the diet plus physical activity groups compared with 10 in 2050 participants in the comparator groups (RR 1.12, 95% CI 0.50 to 2.50; 95% prediction interval 0.44 to 2.88; 4099 participants, 10 trials; very low-quality evidence). The definition of T2DM incidence varied among the included trials. Altogether 315 of 2122 diet plus physical activity participants (14.8%) developed T2DM compared with 614 of 2389 comparator participants (25.7%) (RR 0.57, 95% CI 0.50 to 0.64; 95% prediction interval 0.50 to 0.65; 4511 participants, 11 trials; moderate-quality evidence). Two trials reported serious adverse events. In one trial no adverse events occurred. In the other trial one of 51 diet plus physical activity participants compared with none of 51 comparator participants experienced a serious adverse event (low-quality evidence). Cardiovascular mortality was rarely reported (four of 1626 diet plus physical activity participants and four of 1637 comparator participants (the RR ranged between 0.94 and 3.16; 3263 participants, 7 trials; very low-quality evidence). Only one trial reported that no non-fatal myocardial infarction or non-fatal stroke had occurred (low-quality evidence). Two trials reported that none of the participants had experienced hypoglycaemia. One trial investigated health-related quality of life in 2144 participants and noted that a minimal important difference between intervention groups was not reached (very low-quality evidence). Three trials evaluated costs of the interventions in 2755 participants. The largest trial of these reported an analysis of costs from the health system perspective and society perspective reflecting USD 31,500 and USD 51,600 per quality-adjusted life year (QALY) with diet plus physical activity, respectively (low-quality evidence). There were no data on blindness or end-stage renal disease.One trial compared a diet-only intervention with a physical-activity intervention or standard treatment. The participants had IGT. Three of 130 participants in the diet group compared with none of the 141 participants in the physical activity group died (very low-quality evidence). None of the participants died because of cardiovascular disease (very low-quality evidence). Altogether 57 of 130 diet participants (43.8%) compared with 58 of 141 physical activity participants (41.1%) group developed T2DM (very low-quality evidence). No adverse events were recorded (very low-quality evidence). There were no data on non-fatal myocardial infarction, non-fatal stroke, blindness, end-stage renal disease, health-related quality of life or socioeconomic effects.Two trials compared physical activity with standard treatment in 397 participants. One trial included participants with IGT, the other trial included participants with IGT, IFG or both. One trial reported that none of the 141 physical activity participants compared with three of 133 control participants died. The other trial reported that three of 84 physical activity participants and one of 39 control participants died (very low-quality evidence). In one trial T2DM developed in 58 of 141 physical activity participants (41.1%) compared with 90 of 133 control participants (67.7%). In the other trial 10 of 84 physical activity participants (11.9%) compared with seven of 39 control participants (18%) developed T2DM (very low-quality evidence). Serious adverse events were rarely reported (one trial noted no events, one trial described events in three of 66 physical activity participants compared with one of 39 control participants - very low-quality evidence). Only one trial reported on cardiovascular mortality (none of 274 participants died - very low-quality evidence). Non-fatal myocardial infarction or stroke were rarely observed in the one trial randomising 123 participants (very low-quality evidence). One trial reported that none of the participants in the trial experienced hypoglycaemia. One trial investigating health-related quality of life in 123 participants showed no substantial differences between intervention groups (very low-quality evidence). There were no data on blindness or socioeconomic effects.

AUTHORS' CONCLUSIONS

There is no firm evidence that diet alone or physical activity alone compared to standard treatment influences the risk of T2DM and especially its associated complications in people at increased risk of developing T2DM. However, diet plus physical activity reduces or delays the incidence of T2DM in people with IGT. Data are lacking for the effect of diet plus physical activity for people with intermediate hyperglycaemia defined by other glycaemic variables. Most RCTs did not investigate patient-important outcomes.