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ScienceWeek
MEDICAL BIOLOGY: COFFEE CONSUMPTION AND TYPE 2 DIABETES
The following points are made by R.M. van Dam and F.B. Hu (J. Am. Med. Assoc. 2005 294:97):
1) Type 2 diabetes is a chronic disease associated with high rates of morbidity and premature mortality.[1] An alarming increase in the prevalence of type 2 diabetes is expected,[2] and the need for preventive action is widely acknowledged. While increased physical activity and restriction of energy intake can substantially reduce the incidence of type 2 diabetes,[3,4] insight into the role of other lifestyle factors may contribute to additional prevention strategies for type 2 diabetes.
2) Coffee is among the most widely consumed beverages in the world.[5] Knowledge of both the positive and negative health effects of coffee is important to allow individuals to make informed choices regarding coffee consumption. In addition, data on the health effects of different coffee constituents and of different types of coffee can contribute to disease prevention. For example, switching from pot-boiled to filtered coffee lowers serum low-density lipoprotein cholesterol concentrations, which may have contributed to the marked reduction of the incidence of coronary heart disease in Finland. Coffee contains numerous substances; among them, caffeine, chlorogenic acid, quinides, and magnesium have been shown to affect glucose metabolism in animal or metabolic studies. Coffee consumption has been extensively studied in relation to various diseases, but not until recently has it been examined in relation to risk of type 2 diabetes. In a Dutch study, higher coffee consumption was associated with a substantially lower risk of type 2 diabetes. This finding has been confirmed in several, but not all, subsequent studies.
3) Several plausible mechanisms for a beneficial effect of coffee on glucose metabolism exist. Coffee has been shown to be a major contributor to the total in vitro antioxidant capacity of the diet, which may be relevant as oxidative stress can contribute to the development of type 2 diabetes. Coffee is the major source of the phenol chlorogenic acid. Intake of chlorogenic acid has been shown to reduce glucose concentrations in rats, and intake of quinides, degradation products of chlorogenic acids, increased insulin sensitivity in rats. Chlorogenic acid contributes to the antioxidant effects of coffee, may reduce hepatic glucose output through inhibition of glucose-6-phosphatase, and may improve tissue mineral distribution through its action as a metal chelator. In addition, chlorogenic acid acts as a competitive inhibitor of glucose absorption in the intestine. Indeed, decaffeinated coffee seemed to delay intestinal absorption of glucose and increased glucagon-like peptide-1 concentrations in an intervention study in humans. Glucagon-like peptide-1 is well known for its beneficial effects on glucose-induced insulin secretion and insulin action. This effect may explain the observation that higher coffee consumption was associated with lower postload, rather than fasting, glucose concentrations.
4) Caffeine ingestion can acutely reduce glucose storage, but beneficial effects of caffeine on lipid oxidation and uncoupling protein-3 expression have also been suggested. In US studies, decaffeinated coffee consumption was inversely associated with risk of type 2 diabetes. In addition, in a Japanese study, the inverse association with hyperglycemia was stronger for coffee than for caffeine. These observations suggest that coffee components other than caffeine may have beneficial effects on risk of type 2 diabetes. Coffee also contains substantial amounts of magnesium, which has been linked to better insulin sensitivity and insulin secretion. However, adjustment for magnesium intake did not explain the association between coffee consumption and risk of type 2 diabetes.
5) The authors systematically reviewed all available epidemiological evidence on the relation between habitual coffee consumption and risk of type 2 diabetes. The authors conclude that their systematic review supports the hypothesis that habitual coffee consumption is associated with a substantially lower risk of type 2 diabetes. Longer-term intervention studies of coffee consumption and glucose metabolism are warranted to examine the mechanisms underlying the relationship between coffee consumption and type 2 diabetes.
References (abridged):
1. Nathan DM. Long-term complications of diabetes mellitus. N Engl J Med. 1993;328:1676-1685
2. Wild S, Roglic G, Green A, Sicree R, King H. Globalprevalence of diabetes: estimates for the year 2000 and projections for 2030. Diabetes Care. 2004;27:1047-1053
3. Tuomilehto J, Lindstrom J, Eriksson JG, et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med. 2001;344:1343-1350
4. Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med. 2002;346:393-403
5. Schaefer B. Coffee consumption and type 2 diabetes mellitus [letter]. Ann Intern Med. 2004;141:321
J. Am. Med. Assoc. http://www.jama.com
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Related Material:
ON DIABETES, OBESITY, AND ADIPOCYTES
The following points are made by A.R. Shuldiner et al (New Engl. J. Med. 2001 345:1345):
1) Although 100 years ago type 2 diabetes mellitus was considered a rare disease, there has recently been an explosive increase in its incidence: currently, approximately 16 million Americans have type 2 diabetes, and at least an equal number have impaired glucose tolerance. Insulin resistance and hyperinsulinemia are characteristic of both type 2 diabetes and impaired glucose tolerance. These metabolic derangements, combined with the hypertension and abnormal blood lipids that are common in type 2 diabetes and impaired glucose tolerance, markedly increase the risk of cardiovascular, peripheral vascular, and cerebrovascular disease.
2) Why has the incidence of type 2 diabetes increased so rapidly? Considerable epidemiologic evidence points to excess caloric intake and physical inactivity as the major reasons. A chronic imbalance between energy expenditure and energy intake causes obesity, which is one of the most potent risk factors for insulin resistance and type 2 diabetes. These epidemiologic observations underscore the importance of the relation of adipose tissue to insulin resistance and glucose intolerance.
3) Recent studies have transformed our thinking about the adipocyte. This cell type is no longer regarded as a passive depot for storing excess energy in the form of triglycerides, but as a cell that actively regulates the pathways responsible for energy balance and whose activity is controlled by a complex network of hormonal and neuronal signals. Indeed, the adipocyte secretes chemical messengers that include leptin, tumor necrosis factor alpha, angiotensinogen, and adiponectin. The most recently discovered adipocyte-secreted hormone is resistin, which may be an important link between increased fat mass and insulin resistance.
New Engl. J. Med. http://www.nejm.org
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Related Material:
GLOBAL AND SOCIETAL IMPLICATIONS OF THE DIABETES EPIDEMIC
The following points are made by Paul Zimmet et al (Nature 2001 414:782):
1) Diabetes mellitus, long considered a disease of minor significance to world health, is now taking its place as one of the main threats to human health in the 21st century(1). The past two decades have seen an explosive increase in the number of people diagnosed with diabetes worldwide(2,3). Pronounced changes in the human environment, and in human behavior and lifestyle, have accompanied globalization, and these have resulted in escalating rates of both obesity and diabetes. Hence the recent adoption of the term "diabesity"(4), first suggested by Shafrir several decades ago(5).
2) There are two main forms of diabetes. Type 1 diabetes is due primarily to autoimmune-mediated destruction of pancreatic beta-cell islets, resulting in absolute insulin deficiency. People with type 1 diabetes must take exogenous insulin for survival to prevent the development of ketoacidosis. Its frequency is low relative to type 2 diabetes, which accounts for over 90% of cases globally. Type 2 diabetes is characterized by insulin resistance and/or abnormal insulin secretion, either of which may predominate. People with type 2 diabetes are not dependent on exogenous insulin, but may require it for control of blood glucose levels if this is not achieved with diet alone or with oral hypoglycemic agents.
3) The diabetes epidemic relates particularly to type 2 diabetes, and is taking place both in developed and developing nations. Paradoxically, part of the problem relates to the achievements in public health during the 20th century, with people living longer owing to elimination of many of the communicable diseases. Non-communicable diseases such as diabetes and cardiovascular disease have now become the main public health challenge for the 21st century, as a result of their impact on personal and national health and the premature morbidity and mortality associated with the non-communicable diseases.
4) In summary: Changes in human behavior and lifestyle over the last century have resulted in a dramatic increase in the incidence of diabetes worldwide. The epidemic is chiefly of type 2 diabetes and also the associated conditions known as "diabesity" and "metabolic syndrome". In conjunction with genetic susceptibility, particularly in certain ethnic groups, type 2 diabetes is brought on by environmental and behavioral factors such as a sedentary lifestyle, overly rich nutrition and obesity. The prevention of diabetes and control of its micro- and macrovascular complications will require an integrated, international approach if we are to see significant reduction in the huge premature morbidity and mortality it causes.
References (abridged):
1. Zimmet, P. Globalization, coca-colonization and the chronic disease epidemic: can the doomsday scenario be averted? J. Intern. Med. 247, 301-310 (2000)
2. Amos, A., McCarty, D. & Zimmet, P. The rising global burden of diabetes and its complications: estimates and projections to the year 2010. Diabetic Med. 14, S1-S85 (1997)
3. King, H., Aubert, R. & Herman, W. Global burden of diabetes, 1995-2025. Prevalence, numerical estimates and projections. Diabetes Care 21, 1414-1431 (1998)
4. Astrup, A. & Finer, N. Redefining type 2 diabetes: 'diabesity' or 'obesity dependent diabetes mellitus'? Obesity Rev. 1, 57-59 (2000)
5. Shafrir, E. Development and consequences of insulin resistance: lessons from animals with hyperinsulinemia. Diabetes Metab. 22, 131-148 (1997)
Nature http://www.nature.com/nature
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Notes by ScienceWeek:
The term "metabolic syndrome" encompasses type 2 diabetes (or prediabetes) and a common constellation of closely linked clinical features. Characteristic factors include insulin resistance per se, obesity (in particular abdominal adiposity), hypertension, and a common form of dyslipidaemia (raised triglycerides and low high-density lipoprotein (HDL)-cholesterol with or without elevation of low-density lipoprotein (LDL)-cholesterol). Metabolic syndrome is associated with a markedly increased incidence of coronary, cerebral and peripheral artery disease.
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