For.men, testosterone is the hormone that determines much more than muscle mass or libido. It controls metabolism, energy, mood, and — most important — immune system function.
When testosterone levels are in equilibrium, the body’s systems work in balance. But when it drops too low,.the effect can ripple through nearly every organ, including the.immune system.

Let’s dismantle how testosterone is manufactured, how it fuels your body’s metabolism, and how that directly corresponds to your immune health.

1. How Testosterone is Manufactured in Men
Most of the testosterone in men is manufactured in the testes (approximately 95%), and the remaining portion is manufactured by the adrenal glands. The process is tightly controlled by the hypothalamic–pituitary–gonadal (HPG) axis:
Hypothalamus secretes gonadotropin-releasing hormone (GnRH).
Pituitary gland responds by secreting luteinizing hormone (LH).
LH travels to the testes, stimulating Leydig cells to release testosterone.
Testosterone enters the bloodstream to influence a number of tissues — muscles, bones, brain, fat tissue, and immune cells.
Production peaks early in the morning and drops with age — about 1% per year beyond age 30.

2. Testosterone and Metabolism — The Key to Immunity
Testosterone is more than a muscle builder; it’s a metabolic regulator. Here’s why:
Retains lean muscle mass → Muscle mass burns more calories at rest, helping with weight and blood sugar control.

Regulates fat distribution → Healthy testosterone prevents excess visceral (abdominal) fat, a key source of low-grade, chronic inflammation.

Improves insulin sensitivity → Healthy blood sugar reduces metabolic stress and inflammation.

When testosterone is low:
Muscle mass decreases
Fat mass — especially visceral fat — increases
Insulin resistance may emerge
Chronic low-grade inflammation rises
This metabolic imbalance is one of the main pathways by which low testosterone damages immune function.

3. Testosterone’s Function in the Immune System
Immunomodulation
Testosterone acts on immune cells directly via androgen receptors:
Suppresses runaway inflammation by decreasing pro-inflammatory cytokines (e.g., TNF-α, IL-6).
Promotes balanced immunity by regulating T cell function and preventing overactive immune reactions that destroy healthy tissue.

Autoimmunity
Men tend to have lower rates of autoimmune disease compared to women, partly because testosterone has anti-inflammatory properties. When testosterone is significantly below normal, the risk for some autoimmune diseases can rise.

Infection Response
Healthy testosterone allows the immune system to respond well without generating harmful “cytokine storms” that are linked to poor infection outcomes. Research conducted during the COVID-19 pandemic ended up concluding that low-testosterone men experienced worse illness outcomes.

4. Causes of Low Testosterone in Men
Aging (natural decline after age 30–35)
Obesity and metabolic syndrome
Chronic stress (too much cortisol suppresses testosterone)
Poor sleep
Chronic disease (diabetes, kidney or liver disease)
Certain drugs (opioids, steroids)

5. Five Ways Your Testosterone May Be Damaging Your Immune Health
1. Chronic fatigue
2. Unexplained weight gain (especially around the middle)
3. Recurring colds or lingering illness
4. Loss of muscle mass despite working out
5. Mood changes, brain fog, or lack of energy


6. Guarding Testosterone — Guarding Your Immunity
Lifestyle Strategies
Strength Training — Naturally stimulates testosterone production and preserves muscle.
Healthy Body Composition — Keep visceral fat low to reduce inflammation.
Prioritize Sleep — 7–9 hours of sleep per night; most testosterone is released during deep sleep.
Balanced Nutrition —Lean protein for muscle repair
Healthy fats (omega-3s, olive oil, avocado) for hormone production
Zinc, magnesium, and vitamin D for hormonal balance
Stress Management — Meditation, deep breathing, or spending time outdoors to reduce cortisol.
Limit Alcohol & No Smoking — Both will impede hormone synthesis and immune function.

Medical Evaluation
When changes in lifestyle do not improve symptoms, a total and free testosterone blood test will verify deficiency.
Treatment options are:
Treatment for underlying medical ailments
Medically supervised testosterone replacement therapy (TRT), if needed

Bottom Line
In males, testosterone is not just a hormone of physiological function — it is also a major controller of metabolism and immunity. As long as testosterone levels are normal, the metabolism purrs like a well-oiled machine, inflammation is managed, and the immune system responds to danger in the proper manner.

By maintaining muscle mass, weight control, high-quality sleep, and medical consultation as needed, men can maintain both their testosterone and their immune strength — deep into the older decades of life.