New research presented at the Endocrine Society’s annual meeting suggests that even modest increases in blood sugar may affect men’s sexual and reproductive health, potentially more than age or testosterone levels.
The study followed healthy men aged 18 to 85 over several years and found that sperm movement and erectile function declined in those with slightly elevated blood sugar levels, even if those levels were still below the threshold for diabetes.
“Although age and testosterone levels have long been considered an impetus for men’s declining sexual health, our research indicates that these changes more closely correlate with modest increases in blood sugar and other metabolic changes,” said lead researcher Dr. Michael Zitzmann, professor of medicine at University Hospital in Muenster, Germany.
The findings come from the FAME 2.0 study, a long-term project that began in 2014 and tracked 200 healthy men who did not have diabetes, heart disease or cancer. By 2020, 117 participants remained. Researchers analyzed hormone levels, semen quality, erectile function and markers of metabolic health, including blood sugar levels (measured by HbA1c) and body mass index.
Over time, most hormone and semen levels remained within normal ranges. But declines in sperm motility and erectile function were linked to blood sugar levels that were elevated, yet still below the diagnostic threshold for diabetes. Testosterone levels were not associated with erectile function but did appear to influence libido.
“We now know that it’s in our power to retain sexual and reproductive wellbeing in men, even as they age,” Zitzmann said. “This means that men can take steps to preserve or revive their reproductive health with lifestyle choices and appropriate medical interventions.”
The researchers hope the study will help physicians better understand how metabolic health impacts sexual function, and that men will be empowered to protect their health by managing blood sugar through diet, activity and preventive care.
This research was part of the FAME 2.0 study and presented at ENDO 2025, the Endocrine Society’s annual meeting. It has not yet been published in a peer-reviewed journal.