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IGT Tied to Increased Mortality

A study in Diabetes Care showed that 74.7% of deaths among patients with impaired glucose tolerance happened after progression to type 2 diabetes.

A July 13 study published online in Diabetes Care found increased risk of mortality in patients with impaired glucose tolerance (IGT), with progression to type 2 diabetes the key risk factor.

This study is an epidemiological analysis of the 23-year follow-up study of participants with IGT from the Da Qing Diabetes Prevention Study to examine the extent to which IGT alone and the subsequent development of diabetes influence mortality.

Researchers from the Chinese Academy of Medical Sciences in Beijing compared mortality before and after diabetes development in 542 patients with IGT. Participants were enrolled in a six-year lifestyle diabetes prevention trial and were followed for 23 years from 1986 to 2009.

During the 23-year follow-up, 174 (32.1%) died, with an overall death rate of 15.9/1,000 person-years. The majority of deaths (74.7%; 130 of 174) occurred after progression to type 2 diabetes, with age-adjusted death rates of 11.1/1,000 person-years before and 19.4/1,000 person-years after the development of type 2 diabetes. The cumulative mortality was 37.8%  in participants who developed type 2 diabetes during first 10 years of follow-up, 28.6% in those who progressed to type 2 diabetes in 10–20 years, and 13.9%  in those who did not develop to type 2 diabetes within 20 years. Time-dependent multivariate Cox proportional hazards analyses, with adjustment for baseline age, sex, intervention, and other potential confounding risk factors, showed that the development of type 2 diabetes was associated with a 73% higher risk of death.

In 2010–11, an estimated 92-113 million adults in China had diabetes, and approximately 100 million others had impaired glucose tolerance (IGT), placing them at high risk of developing the disease. While excess risk for death among people with diabetes is well-documented in Western populations and in some Asian populations, IGT also predicts excess mortality. Most studies of mortality in people with IGT have had relatively short-term follow-up and lack follow-up evaluations to determine whether they subsequently developed diabetes. The extent that the excess mortality is attributable to IGT itself or is attributable to diabetes, which develops in many with IGT, is controversial.

Qiao et al. examined this question in a Finnish population and concluded that IGT is an independent risk predictor for all-cause mortality and that the excess risk in people with IGT cannot be explained by the subsequent development of overt diabetes. However, two other studies, also with follow-up to identify incident diabetes, concluded that the excess mortality in those with impaired fasting glucose (IFG) and IGT occurs primarily among those who developed type 2 diabetes, and that the risk increases with increasing duration of type 2 diabetes. Understanding the extent to which IGT itself or the subsequent development of type 2 diabetes influences excess mortality has important implications for the design, conduct, and utility of diabetes prevention programs.

Distinguishing between these possibilities is crucial to the design and conduct of diabetes prevention programs, and ultimately their importance. If the excess mortality associated with IGT occurs mainly after the development of diabetes, then delaying or preventing the development of diabetes may be expected to lower mortality risk. Conversely, if the excess mortality is primarily associated with IGT (or IFG) and is not related to progression to type 2 diabetes, then delaying or preventing type 2 diabetes may have little or no effect in reducing excess mortality.

This study is to our knowledge the first long-term, population-based cohort study of mortality related to IGT in China. IGT was associated with increased risk of death, but much of the increase was the result of the subsequent development of type 2 diabetes in many of those with IGT.  The results provide a strong rationale for type 2 diabetes prevention in people with IGT because they indicate that the risk of death in people with IGT is much lower before than after the development of type 2 diabetes.

The researchers concluded from the results that IGT is associated with increased risk of mortality, but much of this excess risk is attributable to the development of type 2 diabetes.

Practice Pearls

  • 74.7% of deaths among patients with IGT happened after progression to type 2 diabetes.
  • Study provides a strong rationale to prevent pre-diabetes turning into diabetes.
  • Preventing the progression to diabetes has a major impact on the quality and duration of life.

 

Diabetes Care Publish Ahead of Print, published online July 13, 2016