The widely used diabetes drug, metformin, may weaken the gains from exercise, new research suggests.
More than 450 million people across the world have type 2 diabetes, and treatment often hinges on lifestyle changes alongside medication.
For nearly half a century, doctors have prescribed metformin and recommended daily physical activity to diabetes patients, on the basis that using both together improves outcomes.
Researchers say metformin may undermine the beneficial effects of physical training.
Metformin reduces blood glucose levels by inhibiting the liver’s glucose production and by helping cells use their own insulin more effectively.
Rutgers University kinesiologist Steven Malin, an author of the new study, said: “Most health care providers assume one plus one equals two.
“The problem is that most evidence shows metformin blunts exercise benefits.”
Researchers say the latest findings raise urgent questions for doctors about how the two therapies can be better combined.
The study recruited 72 adults at risk of metabolic syndrome – a cluster of conditions that raise the risk of diabetes and heart disease – and divided them into four groups: high-intensity exercise with placebo, high-intensity with metformin, low-intensity with placebo, and low-intensity with metformin.
For four months, researchers tracked changes in how participants’ blood vessels responded under insulin stimulation, a process known to help vessels dilate and deliver oxygen, hormones and nutrients after meals.
They found that exercise helped the blood vessels respond better to insulin, allowing more blood flow to muscles, but these improvements shrank if metformin was added.
Metformin also appeared to diminish gains from aerobic exercise and reduce the positive effects on inflammation and fasting glucose.
Researchers suspect the very process that makes metformin effective may be blocking the body’s ability to respond fully to physical training.
Dr Malin noted: “Blood vessel function improved with exercise training, regardless of intensity.”
He added: “Metformin blunted that observation, suggesting one type of exercise intensity isn’t better either with the drug for blood vessel health.
“People taking metformin also did not gain fitness. That means their physical function isn’t getting better and that could have long-term health risk.”
Researchers call for further studies to find strategies that preserve the benefits of both exercise and metformin.
Dr Malin said: “We need to figure out how to best recommend exercise with metformin.
“We also need to consider how other medications interact with exercise to develop better guidelines for doctors to help people lower chronic disease risk.”