Metformin May Blunt Exercise Benefits in Diabetes Prevention, Rutgers Study Finds
Key Insights
A Rutgers study of 72 adults at risk for metabolic syndrome (search) found that metformin blunts improvements in blood vessel function, fitness, and blood sugar control typically achieved through exercise.
Researchers discovered that while exercise alone improved vascular insulin sensitivity and blood flow to muscles, adding metformin reduced these beneficial effects.
The findings challenge the long-held medical assumption that combining metformin with exercise provides additive benefits for diabetes (search) and heart disease (search) prevention.
A new study from Rutgers University challenges a fundamental assumption in diabetes (search) care, revealing that metformin—one of the world's most prescribed diabetes medications—may actually counteract the beneficial effects of exercise. The research, published in The Journal of Clinical Endocrinology & Metabolism, found that the drug blunts critical improvements in blood vessel function, fitness, and blood sugar control that normally result from physical activity.
Study Design and Methodology
Researchers recruited 72 adults at risk for metabolic syndrome (search), a cluster of conditions that increase the risk of diabetes (search) and heart disease (search). Participants were divided into four groups: high-intensity exercise with placebo, high-intensity exercise with metformin, low-intensity exercise with placebo, and low-intensity exercise with metformin.
For 16 weeks, the research team tracked changes in blood vessel function under insulin stimulation—a key process that helps blood vessels dilate and deliver oxygen, nutrients, and hormones after meals. This vascular response is crucial because insulin's ability to open blood vessels helps shuttle glucose out of the bloodstream and into tissues, lowering blood sugar after meals.
Unexpected Findings Challenge Medical Practice
The results revealed a striking contradiction to current medical practice. Exercise alone improved vascular insulin sensitivity, meaning blood vessels responded better to insulin and allowed increased blood flow to muscles. However, when metformin was added to the exercise regimen, these improvements diminished significantly.
"Most health care providers assume one plus one equals two," said Steven Malin, a professor in the Department of Kinesiology and Health at Rutgers and lead author of the study. "The problem is that most evidence shows metformin blunts exercise benefits."
The medication also lowered gains in aerobic fitness and reduced the positive effects on inflammation and fasting glucose levels. "Blood vessel function improved with exercise training, regardless of intensity. Metformin blunted that observation, suggesting one type of exercise intensity is not better either with the drug for blood vessel health," Malin explained.
Clinical Implications for Diabetes Management
These findings carry significant implications for the nearly 38 million Americans with type 2 diabetes (search) and the more than 450 million people worldwide affected by the condition. Since 2006, healthcare providers have routinely recommended that patients with high blood sugar take metformin while engaging in regular exercise, believing the combination would deliver superior results.
"If you exercise and take metformin and your blood glucose does not go down, that's a problem. People taking metformin also didn't gain fitness. That means their physical function isn't getting better and that could have long-term health risks," Malin noted.
The mechanism behind metformin's interference with exercise benefits remains unclear, though researchers suspect it may relate to the drug's primary mode of action. Metformin reduces blood glucose levels by inhibiting the liver's glucose production and helping cells use their own insulin more effectively—processes that may inadvertently block the body's ability to respond fully to physical training.
Need for New Treatment Guidelines
The researchers emphasize that their findings should not prompt patients to discontinue metformin or exercise, both of which remain proven therapies for diabetes (search) management. Instead, the study highlights an urgent need to develop better guidelines for combining these treatments.
"We need to figure out how to best recommend exercise with metformin," Malin said. "We also need to consider how other medications interact with exercise to develop better guidelines for doctors to help people lower chronic disease risk."
The study calls for additional research to identify strategies that can preserve the benefits of both exercise and metformin, potentially through modified dosing schedules, different exercise protocols, or alternative medication timing that could optimize the therapeutic effects of both interventions.