Spotlight on the effects of exercise in diabetes

Several recent studies analyzed the effects of exercise in patients with diabetes.

The first study, published by Diabetes Care on Jan. 16, included 8,528 adult patients with diabetes and a body mass index (BMI) of at least 18.5 kg/m². As part of the Henry Ford Exercise Testing Project, all patients performed a Bruce protocol exercise treadmill stress test between 1991 and 2009. Their fitness levels were categorized by the metabolic equivalents achieved: low (<6), moderate (6 to 9.9), or high (≥10). In follow-up through April 2013, obese patients had a 30% lower mortality risk compared with normal-weight patients. Greater fitness was also associated with lower mortality: Compared with the low-fitness group, patients in the high group had a 70% reduction in mortality risk and those in the moderate group had about a 50% reduction. After adjustment, the study showed that higher BMI was predominantly associated with lower mortality among the low-fitness patients and obese patients with moderate fitness. The study authors concluded that the obesity paradox appears to be less pronounced for patients with the highest fitness level. “While weight loss and improved fitness should both be recommended for patients with diabetes, these observational results highlight the need for further research to test whether prevention strategies focusing on improving fitness may potentially provide a greater reduction in mortality than weight-loss interventions,” they wrote.

A second study, published by Diabetologia on Jan. 20, looked at changes in cardiorespiratory fitness and indicators of vascular health among 63 patients with type 2 diabetes participating in a yearlong exercise trial. They were randomized to moderate continuous training combined with resistance training, high-intensity interval training, or a control group. Patients were compared by whether their cardiorespiratory fitness improved (defined as at least a 5% increase in peak oxygen consumption) during the trial. The results showed that patients in the exercise groups had significant improvements in carotid intima-media thickness and lower-limb arterial stiffness compared to the nonexercisers, regardless of whether their cardiorespiratory fitness improved. “From a clinical standpoint, when assessing the successfulness of an exercise intervention in individuals with type 2 diabetes, practitioners should not overlook the impact of exercise training on other health indicators by simply focusing on [cardiorespiratory fitness], as other favourable health benefits are still obtainable with exercise in this patient population despite lack of improvements in fitness,” the study authors wrote.

Finally, a study published by Mayo Clinic Proceedings on Jan. 30 assessed medication use and cardiovascular risk factors among 92 patients with type 2 diabetes participating in a trial of a lifestyle intervention. All patients received lifestyle advice and target-driven medication management, and two-thirds also received supervised exercise and individualized dietary counseling. The exercise group was divided into tertiles by minutes of exercise completed per week (median minutes per week in each tertile: 178, 296, and 380). Greater amounts of exercise were associated with higher odds of being able to discontinue glucose-lowering medication (number needed to treat in the respective tertiles: 4, 3, and 2). Only the two higher-exercise groups showed significant differences in cardiovascular risk factors such as levels of HbA1c, fitness, two-hour glucose, and triglycerides compared to controls. The study authors concluded that lower levels of exercise are sufficient to affect medication use, but “insofar as remission is a goal, our data suggest that prescribed exercise volumes may need to exceed current recommendations.” They added that “the feasibility of such high volumes of exercise can be questioned” and called for randomized trials to confirm the findings.