Testosterone in Men: What It Is, Why It Matters & What 2025 Research Reveals

When most men think about testosterone, they think of muscles, libido, and masculinity. But this hormone does far more than fuel physical strength or sexual drive. Testosterone is central to men’s health across the lifespan—shaping mood, metabolism, bone strength, cardiovascular function, and even inflammation.

The latest research in 2025 is helping us better understand how testosterone affects the body, how deficiencies develop, and what treatment options look like for men of different ages.

How Testosterone Works

Testosterone is the body’s primary androgen, or male sex hormone. It’s mainly produced in the testes, under the control of the brain’s hypothalamic-pituitary-gonadal axis. Signals from the hypothalamus trigger the pituitary gland to release luteinizing hormone (LH), which stimulates testosterone production.

Once in the bloodstream, testosterone binds to receptors throughout the body—affecting tissues as diverse as the brain, bones, blood vessels, and muscles.

Key Functions of Testosterone

Testosterone is not just about reproduction—it influences nearly every system in the body.

• Reproductive health & libido – Regulates sexual desire, erectile function, and sperm production.

• Body composition – Promotes lean muscle, reduces abdominal fat, and stimulates red blood cell production.

• Bone & metabolic health – Maintains bone density and helps regulate glucose and fat metabolism.

• Mood, cognition & energy – Supports motivation, concentration, and overall vitality.

• Heart & vascular health – Plays a role in inflammation, blood vessel flexibility, and cardiovascular risk.

What the Latest Research Says (2025)

The science of testosterone is evolving fast. Here are some of the key findings shaping how we view men’s health today:

1. Testosterone’s broad physiological role

A major review published in UroPrecision this year underscored that testosterone impacts far more than sexual function. It highlighted wide-ranging effects on cardiovascular, metabolic, and immune health—making testosterone deficiency a systemic health issue, not just a quality-of-life problem.

2. Benefits in older men

Large randomized trials show that testosterone therapy in older men can:

• Improve sexual function, mood, and energy.

• Increase bone mineral density and hemoglobin.

• Help prevent or reverse type 2 diabetes.

Importantly, recent long-term studies report reassuring safety data on cardiovascular and prostate risks—two areas of previous concern.

3. Testosterone and inflammation

A 2025 study found that men with low testosterone had higher levels of the inflammatory marker hsCRP. This supports what we see clinically—that hypogonadism is linked to increased systemic inflammation and chronic disease risk.

4. GLP-1 weight-loss drugs boost testosterone

One of the more surprising findings this year: men using GLP-1 receptor agonists (like semaglutide and tirzepatide) for weight loss saw a 53–77% rise in testosterone over 18 months. This is likely due to fat loss (less conversion of testosterone to estrogen by aromatase), reduced inflammation, and improved metabolic health.

5. Hypogonadism is underdiagnosed

Low testosterone becomes more common with age—affecting ~40% of men over 45 and nearly half of men over 80. Symptoms like fatigue, low libido, mood swings, reduced muscle mass, and bone fragility are often brushed off as “just aging”—but may in fact reflect treatable testosterone deficiency.

Practical Takeaways

• Testosterone is about whole-body health, not just masculinity.

• Men with persistent fatigue, low libido, or body composition changes should consider having testosterone checked.

• Lifestyle factors—exercise, nutrition, sleep, and weight management—play a huge role in supporting healthy testosterone.

• When clinically indicated, testosterone therapy can be safe and effective, especially now with stronger evidence in older men.

• Novel therapies like GLP-1 medications may also indirectly improve testosterone by addressing obesity and metabolic dysfunction.

Conclusion

Testosterone is more than a “male hormone”—it’s a foundation of physical and mental health. New research in 2025 highlights its impact on inflammation, metabolism, and long-term disease risk. For men experiencing symptoms or those at risk of deficiency, now is the time to move beyond stigma and take testosterone health seriously.