Cochrane for Clinicians
Putting Evidence into Practice
The Role of Exercise in Patients with Type 2 Diabetes
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Clinical Scenario
A 65-year-old woman with new-onset type 2 diabetes and an A1C level of 8 percent wants to know if she can control her diabetes without taking medications or insulin.
Clinical Question
What should physicians tell patients with type 2 diabetes about the role of exercise?
Evidence-Based Answer
Regular exercise reduces A1C levels, adiposity, and triglyceride levels. However, no research has definitively proved a benefit of exercise on patient-oriented outcomes such as diabetes-related morbidity and mortality.1
Cochrane Abstract
Background: Exercise is generally recommended for persons with type 2 diabetes. However, some studies evaluate an exercise intervention including diet or behavior modification or both, and the effects of diet and exercise are not differentiated. Some exercise studies involve low participant numbers, lacking power to show significant differences that may appear in larger trials.
Objectives: To assess the effects of exercise in type 2 diabetes.
Search Strategy: Trials were identified through the Cochrane Central Register of Controlled Trials (CENTRAL), Medline, EMBASE, and manual searches of bibliographies. Date of last search was March 3, 2005.
Selection Criteria: All randomized controlled trials comparing any type of well-documented aerobic, fitness, or progressive resistance-training exercise with no exercise in persons with type 2 diabetes.
Data Collection and Analysis: Two authors1 independently selected trials, assessed trial quality, and extracted data. Study authors were contacted for additional information. Any information on adverse effects was collected from the trials.
Primary Results: Fourteen randomized controlled trials comparing exercise against no exercise in type 2 diabetes were identified, involving 377 participants. Trial durations ranged from eight weeks to 12 months. Compared with the control, the exercise intervention significantly improved glycemic control as indicated by a decrease in A1C levels of 0.6 percent (-0.6; 95% confidence interval [CI], -0.9 to -0.3; P < .05). This result is statistically and clinically significant. There was no significant difference between groups in whole body mass, probably because of an increase in fat-free mass (muscle) with exercise, as reported in one trial (13.9 lb [6.3 kg]; 95% CI, 0.0 to 27.8 [0.0 to 12.6]). There was a reduction in visceral adipose tissue with exercise (-7.1 square in [-45.5 cm2]; 95% CI, -9.9 to -4.2 [-63.8 to -27.3]), and subcutaneous adipose tissue also decreased. No study reported adverse effects in the exercise group or complications of diabetes. The exercise intervention significantly increased insulin response (131 area under the curve; 95% CI, 20 to 242; one trial), and decreased plasma triglycerides (-22.1 mg per dL [-0.25 mmol per L]; 95% CI, -42.5 to -1.8 [-0.48 to -0.02]). No significant difference was found between groups in quality of life (one trial), plasma cholesterol, or blood pressure.
Reviewers' Conclusions: This meta-analysis shows that exercise significantly improves glycemic control and reduces visceral adipose tissue and plasma triglycerides, but not cholesterol, in persons with type 2 diabetes, even without weight loss.
These summaries have been derived from
Cochrane reviews published in the Cochrane Database of Systematic Reviews in
the Cochrane Library. Their content has, as far as possible, been checked with
the authors of the original reviews, but the summaries should not be regarded
as an official product of the Cochrane Collaboration; minor editing changes
have been made to the text (http://www.cochrane.org).
Practice Pointers
Exercise, diet control, smoking cessation,
and reduction of alcohol use are recommended lifestyle modifications for
persons with type 2 diabetes.2 The American
Diabetes Association recommends that persons with diabetes get at least 150
minutes of aerobic physical activity per week for improvement of glycemic
control, and advocates performance of resistance exercises targeting all major
muscle groups at least three times per week.3
Although some patients may be highly motivated to pursue lifestyle
interventions to avoid the use of insulin or medications, others may see
lifestyle changes as a burden that adds to the complexities of managing type 2
diabetes. Furthermore, there may be skepticism among physicians and patients
about whether exercise can have a clinically meaningful impact on
type 2
diabetes compared with any number of diabetes drugs available.
This Cochrane review provides strong evidence that exercise programs ranging in duration from eight weeks to one year reduce A1C levels by approximately 0.6 percent, as well as reducing adipose tissue and triglyceride levels.1 However, the studies reviewed did not provide definitive evidence of improvement in quality of life, morbidity, or mortality. The durations were insufficient to evaluate changes in mortality rates and there was minimal reporting of quality-of-life measures.
The clinical significance of a 0.6 percent reduction in A1C levels resulting from exercise might be extrapolated by a comparison with the average 1 to 2 percent reduction achieved with most classes of oral hypoglycemic agents.4 In the United Kingdom Prospective Diabetes Study, a 1 percent lower A1C level was associated with a 21 percent lower risk of death related to diabetes, a 14 percent lower risk of myocardial infarction, and a 37 percent lower risk of microvascular complications.5 However, this study did not demonstrate that therapies targeted to reduce A1C levels improved patient-oriented outcomes.6 Therefore, although it has been proven that among persons with diabetes who have lower A1C levels there are fewer deaths, heart attacks, and microvascular complications, there is not yet conclusive evidence that lowering A1C levels through exercise leads to a corresponding risk reduction in patient-oriented outcomes (a benefit that has been demonstrated for tight control of blood pressure and lipid levels in patients with diabetes).
Although common sense seems to support the importance of exercise for type 2 diabetes, there are several issues to consider when applying the evidence to patient care. First, despite evidence that exercise reduces adiposity in patients with type 2 diabetes, exercise should not be recommended as a primary means for weight loss (particularly short-term weight loss) because of the lack of a short-term net reduction in body mass index. Second, although the studies reviewed showed drops in rates of exercise participation, patients who continued to exercise maintained their A1C level reductions-thus, although long-term exercise may not be for everyone, it will benefit those who pursue it. Third, reductions in A1C levels were noted across a wide range of activity levels-from low-intensity, once-weekly qigong to high-intensity progressive resistance training.
REFERENCES
1. Thomas DE, Elliott EJ, Naughton GA. Exercise for type 2 diabetes mellitus. Cochrane Database Syst Rev 2006;(3):CD002968.
2. Diabetes: taking charge of your diabetes. Accessed December 7, 2006, at: http://familydoctor.org/049.xml.
3. American Diabetes Association. Standards of medical care in diabetes-2006. Diabetes Care 2006;29(suppl 1):S4-42.
4. Inzucchi SE. Oral antihyperglycemic therapy for type 2 diabetes: scientific review. JAMA 2002;287:360-72.
5. Stratton IM, Adler AI, Neil HA, Matthews DR, Manley SE, Cull CA, et al. Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes (UKPDS 35): prospective observational study. BMJ 2000;321:405-12.
6. McCormack J, Greenhalgh T. Seeing what you want to see in randomised controlled trials: versions and perversions of UKPDS data. United Kingdom prospective diabetes study. BMJ 2000;320:1720-3.
Address correspondence to William E. Cayley, Jr., M.D., M.Div., at bcayley@yahoo.com. Reprints are not available from the author.
Author disclosure: Nothing to disclose.
The Cochrane Abstract above is a summary of a review from the Cochrane Library. It is accompanied by an interpretation that will help clinicians put evidence into practice. William E. Cayley, Jr., M.D., M.Div., presents a clinical scenario and question based on the Cochrane Abstract, followed by an evidence-based answer and a critique of the review. The practice recommendations in this activity are available at http://www.cochrane.org/reviews/en/ab002968.html.
This clinical content conforms to AAFP criteria for evidence-based continuing medical education (EB CME). See Clinical Quiz on page 307.
The series coordinator for AFP is Clarissa Kripke, M.D., Department of Family and Community Medicine, University of California, San Francisco.
Cochrane Briefs
Clinical Question
Does screening for prostate cancer reduce all-cause or prostate-cancer-specific mortality or impact quality of life?
Evidence-Based Answer
There is insufficient evidence to determine whether screening for prostate cancer reduces mortality or impacts quality of life.
Practice Pointers
This Cochrane review identified two randomized controlled trials (RCTs) comparing mass screening for prostate cancer to no screening: the Quebec trial and the Norrkoping trial. Both studies reported data on prostate cancer incidence, disease-specific mortality, stage at diagnosis, and treatment follow-up. Neither study reported data on quality of life, all-cause mortality, costs, or adverse effects of screening (e.g., false-negative or false-positive results, adverse effects of biopsy, treatment complications). These studies had serious methodologic flaws resulting in a high risk of bias.
The Quebec trial recruited men 45 to 80 years of age from electoral registrations in Quebec City, Canada. A total of 31,133 men were randomly selected to be offered screening, and 15,353 were not invited to screening. Men with prostate cancer and those previously screened and referred to the study's clinic were excluded. Screening was performed annually by a digital rectal examination (DRE) and prostate-specific antigen (PSA) test; by DRE, PSA, and transrectal ultrasound-guided biopsy; or by PSA alone.
The reported relative risk (RR) of death from prostate cancer in men who were screened was 0.39 (95% confidence interval, 0.19 to 0.65). However, only 23 percent of those invited for screening were screened, and 7.3 percent in the nonscreening control group were screened. To address this high rate of crossover from the invited group to the uninvited group, the Cochrane reviewers performed intention-to-treat analysis from the study's raw data. Reanalysis found no difference in prostate-cancer-specific mortality between the two groups at 11-year follow-up.
The second trial recruited men 50 to
69 years
of age from Norrkoping, Sweden, from the national population register. A total
of 9,026 men were identified, with one in six invited to screening (1,494
invited; 7,532 not invited). Exclusion criteria were not reported. Screening
was performed every three years by DRE alone or by DRE and PSA testing. Of
those invited for screening, 70 to 77 percent were screened. There were no data
on how many uninvited men received screening. In the intention-to-treat
analysis, there was no difference between the two groups in
prostate-cancer-specific death at 15-year follow-up.
There are two ongoing large-scale RCTs of prostate cancer screening: the European Randomised study of Screening for Prostate Cancer trial and the Prostate, Lung, Colorectal and Ovarian cancer screening trial. It is anticipated that findings from these two trials will be available in the next few years and will provide the evidence needed to determine whether screening for prostate cancer should be offered routinely. In the meantime, shared decision making-including a discussion of the false-positive and false-negative results of screening tests, the variable natural history of prostate cancer in various individuals, and the uncertainty of the net benefit of early detection and treatment in asymptomatic men-has been recommended by major professional organizations.1-3
Source: Ilic D, et al. Screening for prostate cancer. Cochrane Database Syst Rev 2006;(3):CD004720.
REFERENCES
1. U.S. Preventive Services Task Force. Screening for prostate cancer: recommendation and rationale. Ann Intern Med 2002;137:915-6.
2. Smith RA, von Eschenbach AC, Wender R, Levin B, Byers T, Rothenberger D, et al., for the ACS Prostate Cancer Advisory Committee, ACS Colorectal Cancer Advisory Committee, and ACS Endometrial Cancer Advisory Committee. American Cancer Society guidelines for the early detection of cancer: update of early detection guidelines for prostate, colorectal, and endometrial cancers. Also: update 2001-testing for early lung cancer detection [Published correction appears in CA Cancer J Clin 2001;51:150]. CA Cancer J Clin 2001;51:38-75.
3. Prostate-specific antigen (PSA) best practice policy. American Urological Association (AUA). Oncology (Williston Park) 2000;14:267-72. Accessed December 7, 2006, at: http://www.cancernetwork.com/journals/oncology/o0002e.htm.
Vaccines for Preventing Influenza in Older Patients
Clinical Question
Are influenza vaccines safe and effective in persons 65 years and older?
Evidence-Based Answer
According to data obtained primarily from poor-quality observational studies, influenza vaccination in older persons living in long-term care facilities appears to prevent approximately 45 percent of pneumonia cases, hospital admissions, and influenza-related deaths. In older persons living in the community, influenza vaccination prevents about 25 percent of hospitalizations from influenza or respiratory illness. The vaccines appear to be safe.
Practice Pointers
The authors of this review identified 71 case-control studies, cohort studies, and randomized controlled trials (RCTs) assessing the effectiveness of influenza vaccination against influenza or influenza-like illness; 64 of these studies addressed vaccine effectiveness in older persons.
There were five RCTs addressing vaccine effectiveness, with about 5,000 observations. Because vaccine type, setting, and outcomes were different in each study, conclusions were limited. A meta-analysis of two of these trials with a total of 2,567 patients showed that inactivated vaccines were more effective than placebo against influenza-like illness and influenza in community settings where there is a high viral circulation (vaccine effectiveness [VE] = 43 percent; 95% confidence interval [CI], 21 to 58 percent); pooled data from three RCTs showed that the vaccines were effective against influenza (VE = 58 percent; 95% CI, 34 to 73 percent).
Vaccines appear to be safe. Based on pooled data from four RCTs, local adverse events such as tenderness and sore arm were significantly more common with vaccine than with placebo; however, differences in systemic side effects were not statistically significant between the two groups.
In the cohort studies, healthier patients with better access to health care services may have received the vaccination preferentially, making the comparison groups different at baseline and overestimating the effectiveness of the vaccine. Likewise, the benefits for all-cause mortality found only in observational studies may reflect differences between vaccinated and nonvaccinated groups rather than a true effect. Evidence from RCTs, in which bias is reduced, is limited because of the relatively small total number of patients studied. Because of universal recommendations for influenza vaccination in older persons, it is unlikely that a randomized placebo-controlled trial will be performed to provide the high-quality evidence required.
Overall, these results support the conclusion that vaccination benefit is maximized if those at greatest risk for influenza complications are successfully targeted for vaccination. The effectiveness of vaccination in older persons living in community-based settings was more modest. The Advisory Committee on Immunization Practices recommends annual influenza vaccination for the following groups: persons at high risk for influenza-related complications and severe disease, including children six to 59 months of age, pregnant women, persons 50 years or older, and persons of any age with certain chronic medical conditions; and those who live with or care for persons at high risk.1
Source: Rivetti D, et al. Vaccines for preventing influenza in the elderly. Cochrane Database Syst Rev 2006;(3):CD004876.
REFERENCE
1. Smith NM, Bresee JS, Shay DK, Uyeki TM, Cox NJ, Strikas RA, and the Advisory Committee on Immunization Practices. Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practices (ACIP) [Published correction appears in MMWR Morb Mortal Wkly Rep 2006;55:800]. MMWR Recomm Rep 2006;55(RR-10):1-42.
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