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Effects of Different Modes of Exercise Training on Glucose Control and Risk Factors for Complications in Type 2 Diabetic Patients: a Meta-Analysis

Response to Snowling and Hopkins

¹ Diabetes Division, Department of Clinical Sciences, S. Andrea Hospital, 2nd Medical School, University of Rome, Rome Italy
² Department of Cellular Biotechnology and Hematology, Laboratory of Clinical Chemistry, St. Andrea Hospital, 2nd Medical School, La Sapienza University, Rome, Italy

Address correspondence to Dr. Stefano Balducci, Clinical Science, University of Rome, viale del Policlinico, Rome, 00161, Italy. E-mail: sbalducci{at}esinet.it

We read with great interest the results of the meta-analysis by Snowling and Hopkins (1) on the effects of different modes of exercise training on glucose control and risk factors for complications in type 2 diabetic patients. This most recent meta-analysis of post-2000 randomized controlled trials is perhaps most important because of the size of the cohort (over 1,000 type 2 diabetic patients) and for the study of characteristics and magnitude of effects in more detail than in the previous Boulé meta-analyses (2). Snowling and Hopkins determined that an A1C reduction of 0.8 ± 0.3% is "small" and affirmed in their conclusion that "there are sufficient studies to allow us to conclude that aerobic, resistance, and combined exercise have small to moderate beneficial effects on glucose control in type 2 diabetic patients and small beneficial effects on some related risk factors for complications of diabetes." They thereby suggest that all forms of exercise training produce small benefits in the main measure of glucose control: A1C. I object to this term "small" on two grounds.

First, exercise training has been frequently associated with trivial effects or unclear measures of conventional cardiovascular risk factors, generally in trials of short duration. These measures themselves are affected by many other confounding factors. According to the U.K. Prospective Diabetes Study, exercise therapy can cause an A1C lowering of –0.9% (A1C median 7.0% with intensive therapy vs. 7.9% with conventional therapy) and may reduce retinopathy, nephropathy, and neuropathy in type 2 diabetic patients. Moreover, the overall microvascular complication rate was decreased by 25%, and there was a 25% reduction in diabetes-related deaths, a 7% reduction in all-cause mortality, and an 18% reduction in combined fatal and nonfatal myocardial infarction (3). These results confirm previous conclusions of two randomized clinical trials: the Diabetes Control and Complications Trial and the Stockholm Diabetes Intervention Study. These are not "small" improvements.

Moreover, in our recent study, we have shown that long-term aerobic exercise training can modify the natural history of peripheral diabetic neuropathy or even prevent its onset. The difference in A1C values between two groups through the 4 years of the study was only –0.42% (4). I think it would do us well to remember the positive pleiotrophic effects of continuous physical exercise. Second, exercise training has been associated recently with substantial and positive effects on plasma lipoprotein profile (5), inflammation markers (6), and endothelial dysfunction (7), with probable consequential positive effects on cardiovascular morbidity and mortality.

Finally, it could be deleterious and counterproductive to continuously refer to the idea of "small" benefits, given the notorious difficulty in some medico-scientific circles to accept the idea that physical exercise may constitute therapeutic treatment for a disease such as type 2 diabetes. Despite concrete evidence in favor of exercise as therapy, it is already difficult to translate the proof of benefits of exercise as therapy into everyday practice. It is belittling of the significance of the findings of very real benefits derived from exercise as therapy and, I believe, reflects a dismissive evaluation of our own work and weakens the already fragile applications of the concept of exercise as therapy for diabetic individuals.

While I agree with the authors that it is necessary to investigate the combined effect of exercise, training, diet, and drugs in order to rationalize therapy to achieve the best use and to implement any synergistic effects of a combination therapy, I still affirm that it is a big achievement that, as the authors claim, "the effects of exercise are similar to those of dietary, drug, and insulin treatment." This is no mean result.

References

1. Snowling NJ, Hopkins WG: Effects of different modes of exercise training on glucose control and risk factors for complications in type 2 diabetic patients: a meta-analysis. Diabetes Care 29:2518–2527
   
2. Boulé NG, Kenny GP, Haddad E, Wells GA, Sigal1 RJ: Meta-analysis of the effect of structured exercise training on cardiorespiratory fitness in type 2 diabetes mellitus. Diabetologia 46:1071–1081, 2003[Medline]
   
3. Diabetes Control and Complications Trial Research Group: The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med 329:977–986, 1993[Abstract/Free Full Text]
   
4. Balducci S, Iacobellis G, Parisi L, Di Biase N, Calandriello E, Leonetti F, Fallucca F: Exercise training can modify the natural history of diabetic peripheral neuropathy. J Diabetes Complications 20:216–223, 2006[Medline]
   
5. American Diabetes Association: Implications of the United Kingdom Prospective Diabetes Study (Position Statement). Diabetes Care 25 (Suppl. 1):S28–S32, 2002
   
6. Kraus WE, Houmard JA, Duscha BD, Knetzger KJ, Wharton MB, McCartney JS, Bales CW, Henes S, Samsa GP, Otvos JD, Kulkarni KR, Slentz CA: Effects of the amount and intensity of exercise on plasma lipoproteins. N Engl J Med 347:1483–1492, 2002[Abstract/Free Full Text]
   
7. Soinio M, Marniemi J, Laasko M, Lehto S, Ronnemaa T: High-sensitivity C-reactive protein and coronary heart disease mortality in patients with type 2 diabetes: a 7-year follow-up study. Diabetes Care 29:329–333
   
8. Fuchsjäger-Mayrl G, Pleiner J, Wiesinger GF, Sider AE, Quittan M, Nuhr MJ, Francesconi C, Seit H-P, Francesconi M, Schmetterer L, Wolzt M: Exercise training improves vascular endothelial function in patients with type 1 diabetes. Diabetes Care 25:1795–1801
   

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				N. J. Snowling and W. G. Hopkins Effects of Different Modes of Exercise Training on Glucose Control and Risk Factors for Complications in Type 2 Diabetic Patients: a Meta-Analysis: Response to Balducci et al. Diabetes Care, April 1, 2007; 30(4): e26 - e26. [Full Text] [PDF]

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