Low Testosterone Isn't the Culprit—Sugar Is

The Hidden Link Between Blood Sugar and Sexual Health

It’s common for middle-aged men to experience a decline in libido or sexual performance. For many years, aging or low testosterone were often cited as the main causes. However, new research is shedding light on a different, more subtle factor: blood sugar levels.

A long-term study presented at the Endocrine Society’s annual meeting in San Francisco found that even small increases in a key blood sugar marker can lead to a decline in sperm movement and erectile function, even in men who are not diabetic. This suggests that blood sugar may be playing a more significant role in sexual health than previously thought.

Understanding the Research

The study, part of the FAME 2.0 project, followed 200 healthy men aged 18 to 85 over six years. None had diabetes, heart disease, or cancer. By 2020, 117 participants remained. Researchers assessed their semen quality, hormone levels, and metabolic health, with a focus on hemoglobin A1c (HbA1c), a marker that reflects average blood sugar levels over the past two to three months.

While hormone levels and semen volume remained within normal ranges, the study found that sperm motility declined significantly in men with rising HbA1c levels, even if their values stayed below the 6.5% threshold that defines diabetes. Erectile function also declined, but only in those whose HbA1c levels increased.

In contrast, testosterone levels, which are often blamed for age-related sexual decline, had little effect on erectile function. Instead, libido appeared to track more closely with testosterone, and even that was influenced by HbA1c levels. This indicates that lifestyle choices and medical interventions can help preserve reproductive health.

The Role of Blood Sugar in Sexual Health

For many men, blood sugar is not something they think about until a diagnosis of diabetes or a warning from their doctor. However, experts warn that ignoring this hidden factor can have serious consequences for long-term health and vitality.

Chronically elevated glucose, even at levels considered “normal,” can damage blood vessels and nerves essential for arousal and performance. According to data from the U.S. Centers for Disease Control and Prevention, nearly one in four Americans with diabetes don’t know they have it. Millions more are in the prediabetic zone without symptoms—except possibly in the bedroom.

This silent erosion is becoming more recognized among physicians. Dr. Jamin Brahmbhatt, a urologist and surgeon, wrote in a recent commentary that sexual health is rarely the first thing people associate with blood sugar. However, chronically high glucose levels can impact intimacy over time, leading to erectile dysfunction before a man is ever diagnosed with or thought to be at risk for diabetes.

Metabolic Health and Aging

The FAME 2.0 study adds weight to this clinical suspicion. By using rigorous semen analyses, hormone assays, and questionnaires, researchers were able to determine which changes were due to age alone and which were linked to blood sugar. The conclusion was clear: metabolic health plays a bigger role than age in sexual and reproductive function.

This finding changes how we think about aging well. A man in his 70s with stable blood sugar may retain better fertility and function than a man in his 40s whose A1c has edged into the prediabetic range.

The Impact of GLP-1 Medications

The growing popularity of GLP-1 medications like semaglutide (Ozempic, Wegovy) for weight loss and blood sugar control is also bringing attention to the connection between metabolic health and sexual function. These drugs, which mimic a gut hormone that regulates appetite and glucose, have shown side benefits ranging from improved sleep to better sexual function.

At the same Endocrine Society meeting, researchers found that testosterone levels increased in men who lost weight on GLP-1 injections—even without direct hormone therapy. The proportion of men with normal testosterone levels jumped from 53% to 77% over 18 months, with an average weight loss of just 10%.

A New Perspective on Health

These findings highlight the close relationship between the body’s metabolic and reproductive systems. Sugar may be influencing more aspects of health than previously understood. As research continues to uncover these links, it becomes increasingly clear that maintaining stable blood sugar levels is crucial for overall well-being, especially when it comes to sexual health.