A Rutgers-led randomized trial reports that the diabetes drug metformin reduced several improvements that typically follow exercise training, including gains in blood vessel function, aerobic fitness and measures of glucose control.
Rutgers researchers, led by Steven Malin of the Department of Kinesiology and Health, report in The Journal of Clinical Endocrinology & Metabolism that adding metformin to a structured exercise program blunted benefits that exercise alone produced. The corrected‑proof abstract describes a double‑blind, placebo‑controlled, 16‑week trial in adults at risk for metabolic syndrome, with participants assigned to low‑ or high‑intensity training while receiving either metformin (2,000 mg/day) or placebo. Vascular insulin sensitivity was assessed with a euglycemic–hyperinsulinemic clamp paired with macro‑ and microvascular measures. Exercise without metformin improved vascular responses and aerobic capacity, but these gains were diminished when metformin was used. (academic.oup.com)
Rutgers’ summary of the study adds that exercise enhanced blood flow to muscles and lowered post‑meal blood sugar, while metformin reduced improvements in blood vessel function, aerobic capacity and markers of inflammation and fasting glucose. Those points align with the journal’s abstract, which reports that VO₂max rose in exercise‑plus‑placebo groups but not when metformin was added, and that metformin attenuated reductions in fasting glucose and inflammatory markers. (sciencedaily.com)
“Blood vessel function improved with exercise training, regardless of intensity. Metformin blunted that observation,” Malin said, according to Rutgers’ news release and ScienceDaily’s write‑up of the study. He added: “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.” (rutgers.edu)
Why might this happen? Rutgers’ materials note that metformin can inhibit aspects of mitochondrial activity—actions that help regulate blood sugar and oxidative stress but may also interfere with some cellular adaptations to training, such as improved mitochondrial efficiency and aerobic performance. These are presented as hypotheses requiring further study. (rutgers.edu)
Participant counts differ across sources. Rutgers’ release says 72 adults were enrolled, divided among four groups by exercise intensity and pill assignment. The journal abstract lists group allocations that sum to 91. It is not immediately clear from public materials whether the larger figure reflects randomization before exclusions, subgroup analyses, or another accounting; the peer‑reviewed abstract is treated here as the primary methodological record. (rutgers.edu)
Context for care: Rutgers’ release notes that, since 2006, medical guidance has encouraged patients with elevated blood sugar to combine metformin with regular exercise. Separately, the American Diabetes Association’s Standards of Care have long recommended structured physical activity for people with diabetes and, for some high‑risk adults with prediabetes, considering metformin in addition to lifestyle modification. Together, these recommendations help explain the interest in how the drug and exercise interact. (rutgers.edu)
The authors and Rutgers emphasize that the findings do not advise stopping either metformin or exercise. Rather, they argue for closer clinical monitoring and more research to determine how best to preserve the benefits of both. (rutgers.edu)
Nearly 35 million Americans are estimated to have type 2 diabetes—a figure consistent with CDC data showing more than 38 million people with diabetes overall, 90–95% of whom have type 2. That prevalence underscores the stakes of optimizing drug–exercise combinations for prevention and care. (cdc.gov)
