Background: It is essential to anticipate and limit the social, economic and sanitary cost of type 2 diabetes (T2D),\nwhich is in constant progression worldwide.\nWhen blood glucose targets are not achieved with diet and lifestyle intervention, insulin is recommended whether\nor not the patient is already taking hypoglycaemic drugs. However, the benefit/risk balance of insulin remains\ncontroversial. Our aim was to determine the efficacy and safety of insulin vs. hypoglycaemic drugs or diet/placebo\non clinically relevant endpoints.\nMethods: A systematic literature review (Pubmed, Embase, Cochrane Library) including all randomised clinical\ntrials (RCT) analysing insulin vs. hypoglycaemic drugs or diet/placebo, published between 1950 and 2013, was\nperformed. We included all RCTs reporting effects on all-cause mortality, cardiovascular mortality, death by\ncancer, cardiovascular morbidity, microvascular complications and hypoglycaemia in adults ââ?°Â¥ 18 years with\nT2D. Two authors independently assessed trial eligibility and extracted the data. Internal validity of studies\nwas analyzed according to the Cochrane Risk of Bias tool. Risk ratios (RR) with 95 % confidence intervals (95 % CI)\nwere calculated, using the fixed effect model in first approach. The I2 statistic assessed heterogeneity. In case of\nstatistical heterogeneity, subgroup and sensitivity analyses then a random effect model were performed. The alpha\nthreshold was 0.05. Primary outcomes were all-cause mortality and cardiovascular mortality. Secondary outcomes\nwere non-fatal cardiovascular events, hypoglycaemic events, death from cancer, and macro- or microvascular\ncomplications.\nResults: Twenty RCTs were included out of the 1632 initially identified studies. 18 599 patients were analysed:\nInsulin had no effect vs. hypoglycaemic drugs on all-cause mortality RR = 0.99 (95 % CI =0.92ââ?¬â??1.06) and\ncardiovascular mortality RR = 0.99 (95 % CI =0.90ââ?¬â??1.09), nor vs. diet/placebo RR = 0.92 (95 % CI = 0.80ââ?¬â??1.07) and\nRR = 0.95 (95 % CI 0.77ââ?¬â??1.18) respectively. No effect was found on secondary outcomes either. However, severe\nhypoglycaemia was more frequent with insulin compared to hypoglycaemic drugs RR = 1.70 (95 % CI = 1.51ââ?¬â??1.91).\nConclusions: There is no significant evidence of long term efficacy of insulin on any clinical outcome in T2D.\nHowever, there is a trend to clinically harmful adverse effects such as hypoglycaemia and weight gain. The only\nbenefit could be limited to reducing short term hyperglycemia. This needs to be confirmed with further studies.
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