International Journal of Diabetes Mellitus 1 (2009) 22–25
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International Journal of Diabetes Mellitus
journal homepage: ees.elsevier.com/locate/ijdm
Review Approach to dysglycemia: Do we need to treat impaired glucose tolerance and impaired fasting glucose?
Mousa A. Abujbara, Kamel M. Ajlouni *
National Center for Diabetes, Endocrinology and Genetics, P.O. Box 13165 Amman 11942, Jordan article info abstract
Article history: Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are not only a surrogate for the state Received 7 October 2008 of insulin resistance but are also associated with the microvascular and macrovascular complications tra- Accepted 7 November 2008 ditionally linked to diabetes. They predict an increased risk for death and morbidity due to cardiovascular disease. There is growing evidence that early detection of this state of ‘‘pre-diabetes” enables us to limit these recognized complications and perhaps to halt the progression to diabetes. For all pre-diabetes patients’ life style modifications, emphasizing modest weight loss & moderate physical activity are strongly rec- ommended. Pharmacological intervention may also be necessary. Many studies have shown several drugs, both antidiabetic and nonhypoglycemic agents to be useful. If pharmacological treatment is required, Metformin is considered the first choice because of its safety, tolerability, efficacy and low cost. Ó 2009 International Journal of Diabetes Mellitus. Published by Elsevier Ltd. All rights reserved.
1. Introduction Between 1997 and 2006, eight major clinical trials examined whether lifestyle or pharmacologic interventions would prevent Diabetes and its complications are a growing concern world- or delay the development of diabetes in populations with IFG wide. It has become an epidemic menace in most developed and/or IGT [4,5,7,12]. All of these trials demonstrated a reduction and many developing countries. Globally, the number of people in the development of diabetes of 25–60% over the period of fol- with diabetes is expected to almost double in the next two low-up depending on the type of intervention applied [8–11]. decades, increasing from 194 million in 2003 to 380 million in 2025 [1]. The associated morbidity, mortality and high costs of health care, made type 2 diabetes an important global public 2. Definition of pre-diabetes and its natural history health challenge and target for prevention. In Jordan, it was esti- mated that the total treatment costs (direct and indirect) incurred The ADA defines normal glucose tolerance as a FPG < 100 mg/dl in regards to diabetes was 1,308 Billion JD per year [2], an enor- and 2 h PG in response to a 75 g OGTT of <140 mg/dl [13]. Diabetes mous public health burden, and made the prevention of diabetes is defined as a FPG P 126 mg/dl or a 2 h PG P 200 mg/dl during an a critical health goal. OGTT. IFG and IGT represent intermediate states of abnormal glu- Progression to overt diabetes from a pre-diabetic state occurs cose regulation that exist between normal glucose homeostasis gradually, over a period of many years; however, current estimates and diabetes. It is a state of heightened risk of developing type 2 indicate that most individuals (perhaps up to 70%) with pre-dia- diabetes and other associated complications. betic state eventually develop diabetes [3–5]. Studies have shown Two different categories of pre-diabetes exist: IFG which is de- that patients during the pre-diabetic state are at increased risk of fined by an elevated fasting plasma glucose (FPG) concentration microvascular (retinopathy, nephropathy and neuropathy) and (P100 and <126 mg/dl) [14] and IGT which is defined by an ele- macrovascular (cardiovascular disease and stroke) complications vated 2-h plasma glucose concentration (P140 and <200 mg/dl) and thus have higher morbidity and mortality than individuals after a 75-g glucose load on the oral glucose tolerance test (OGTT) with normal glucose homeostasis [6]. in the presence of an FPG concentration <126 mg/dl [14]. Studies have shown that an oral glucose tolerance test (OGTT) is a more sensitive measure of early abnormalities in glucose regula- * Corresponding author. Tel.: +962 6 535 3374; fax: +962 6 535 33 76. tion than fasting plasma glucose or HbA1c [6]. This is possibly due E-mail address: [email protected] (K.M. Ajlouni). to the fact that IGT is a consequence of two processes that are
1877-5934/$ - see front matter Ó 2009 International Journal of Diabetes Mellitus. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijdm.2009.03.011 M.A. Abujbara, K.M. Ajlouni / International Journal of Diabetes Mellitus 1 (2009) 22–25 23 intimately associated with obesity and drive pre-diabetic hyper- complications are also present in the pre-diabetic state and that glycemia: insulin resistance and dyslipidemia [15]. In obesity, as their risk increases with the distribution of blood glucose concen- skeletal muscles lose sensitivity to insulin, more glucose is taken tration well below the overt diabetes. The Aus Diab studies, for up by adipocytes, stimulating the production and release of more example, which is a population-based survey of 11,247 adults free fatty acids (FFAs) and triglycerides (TG). Elevated circulating aged over 25 years found that 21.7% of individuals with pre-dia- FFAs in turn promote hyperglycemia by stimulating hepatic betes (IGT and/or IFG) had at least one microvascular complica- gluconeogenesis while inhibiting insulin-mediated glucose uptake tion [22]. and storage as glycogen. In a cross-sectional study, neuropathy was found in 26% of 279 The prevalence of IFG and IGT varies considerably among differ- patients with diabetes, 11.2% of 89 patients with IGT, and only 3.9% ent ethnic groups. Data also indicate that the prevalence of IFG and of 577 age-matched normal control subjects [23]. IGT associated IGT is 26% and 15% respectively [16]. Also in Jordan Ajlouni et al re- neuropathy is a symmetric, distal sensory polyneuropathy with ported the prevalence of pre-diabetes (IFG and IGT) to be 10% in prominent neuropathic pain which is phenotypically similar to dia- 1997 [17]and the prevalence of IFG to be 7.8% in 2004 [18]. The betic neuropathy [24,25]. This reflects similar fiber loss and altered prevalence of IFG and IGT also differs by age and sex, being more nerve morphology in both IGT and diabetes. Autonomic dysfunc- common in women than in men and increasing with advancing tion manifested mainly as vagal dysautonomia (abnormal heart age [19]. rate recovery following exercise, blunted R–R interval variability to deep breathing, and reduced expiration to inspiration ratio) is also prevalent in pre-diabetes [26]. Microalbuminuria also has an increased prevalence in IGT. A very large population based study in China [27] demonstrated that the rate of albumin excretion was significantly higher among IGT subjects compared with the non-diabetic control group (7.2 ± 5.7 vs. 4.5 ± 2.8). Independent studies have noted an approximate fourfold in- crease in the prevalence of retinopathy among Pima Indians with IGT compared with age-matched control subjects [28]. Data suggest that the first stage of retinal injury occurs during IGT [28].
5. Macrovascular complications of prediabetes
A diagnosis of pre-diabetes not only identifies subjects who are at increased risk of diabetes but also at risk of cardiovascular and The course of pre-diabetes (both IGT and IFG) is variable and other macrovascular complications of diabetes. Data have shown difficult to predict. The different rates of progression reflect differ- that IGT patients are at greater risk of death from all causes and ent genetic and environmental factors. Furthermore, patients with have a two to fivefold increased incidence of new-onset cardiovas- both IGT and IFG develop diabetes twice the rate as do individuals cular ischemia, fatal and total myocardial infarction, and stroke in who manifest a single abnormality [20]. Patients with a higher FPG comparison with their age-matched normoglycemic control sub- (i.e. 6.1–6.9 mmol/L [110–125 mg/dL]) are also at much higher risk jects [29,30]. The Paris prospective study [31] has shown during of progression to diabetes than those with lower (but abnormal) the ten year follow up period that subjects with impaired glucose FPG levels (5.6–6.0 mmol/L [100–109 mg/dL]) [4]. tolerance have about 50% increased risk of cardiovascular mortal- ity. Other studies have shown an increased incidence of heart fail- ure and coronary artery disease in patients with IGT irrespective of 3. Pathogenesis of IFG and IGT progression to diabetes [32,33]. While some studies have shown that both IGT and IFG confer an The basic patho-physiological mechanisms underlying pre-dia- increased risk of cardiovascular disease [34], others, like the Funag- betes are insulin resistance and defective insulin secretion. How- ata diabetes study, suggest that IGT is more strongly associated ever, IFG and IGT differ in the nature of both of these defects [21]. with cardiovascular disease risk than with fasting hyperglycemia In isolated IFG, there is a predominant hepatic insulin resistance [29]. with relatively preserved skeletal muscle sensitivity to insulin. On the other hand, in isolated IGT the hepatic insulin sensitivity is nor- 6. Rationale for the prevention of diabetes and mal to slightly reduced and the resistance of skeletal muscles to endations for clinical management insulin is moderate to severe. recomm IFG and IGT also differ in their pattern of impairment of insulin The considerable increase in the incidence of diabetes and its secretion. In isolated IFG there is a decrease in the first-phase (0– serious long term complications strongly support efforts to pre- 10 min) insulin secretory response to intravenous glucose and a re- vent or delay its occurrence. This is the rationale behind the con- duced early-phase (first 30 min) insulin response to oral glucose sensus statement for the management of patients with pre- but the late-phase (60–120 min) plasma insulin response during diabetes released by the ADA in October, 2006. The panel con- the OGTT is normal. In isolated IGT there is a defect in both early cluded that intervention was warranted, based on the expecta- and late-phase insulin secretion. tion that delay of diabetes would postpone the requirement for complicated treatment regimens and that microvascular compli- 4. Microvascular complications of prediabetes cations (and potentially CVD) would be delayed or prevented [13]. Classically diabetes is associated with microvascular and mac- Fortuitously, a wide variety of interventions have been shown rovascular complications but growing evidence shows that these to alter the natural course of IFG and IGT and their progression 24 M.A. Abujbara, K.M. Ajlouni / International Journal of Diabetes Mellitus 1 (2009) 22–25
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Cover Image
Retinal Arteriolar Cholesterol Emboli A funduscopic image of a 59 year old man who was referred due to visual obscuration. Two years prior, multiple retinal arteriolar cholesterol emboli and a saddle embolus superior to the optic nerve was seen (Panel A, arrow). Two months later, an increase in number of cholesterol emboli occurred (Panel B). Four weeks later, whitening in the inferior macular region was noted (Panel C), consistent with an occlusion at the second major bifurcation of the inferior temporal branch of the retinal artery. For further information, please search on: Michael C. Retinal Arteriorlar Cholesterol Emboli. N Engl J Med. Feb 2008. p. 826.