In short: An erection is the result of a finely tuned interplay of nerves, blood vessels, erectile tissue, and hormones. In this article, I explain in a factual and easy-to-understand way the physical processes that lead to an erection, the role testosterone and other hormones play, how a testosterone deficiency in midlife can show up, and when replacement therapy makes sense. I also cover the effects of arginine and citrulline, as well as the importance of ejaculations for health.
How does an erection happen? A brief, factual overview
An erection is not purely a "mechanical" process, but the result of coordinated signals and physical changes:
- Nerve impulses: Sexual arousal — psychological or through direct stimulation — activates parasympathetic nerve pathways in the pelvic area. These nerves release messenger substances, especially nitric oxide (NO).
- Vascular response: NO leads to the production of cGMP in the smooth muscle cells of the arteries and erectile tissue (corpora cavernosa), which relaxes the muscle cells. The arteries widen, and more blood flows into the erectile tissue.
- Mechanical component: The venous outflow pathways are compressed by the filling and expansion of the erectile tissue, so that blood is retained in the penis and a stable erection develops.
- Ending the erection: Enzymes such as phosphodiesterase-5 (PDE5) break down cGMP. Sympathetic activation (e.g. during stress) can also bring it to an end.
The role of testosterone and other hormones
Hormones influence erection and sexual function on several levels:
Testosterone
- Libido: Testosterone is central to sexual desire and arousability.
- Penis physiology: Testosterone supports the health of erectile tissue, the regulation of NO synthase (the enzyme involved in NO production), and affects nerve function.
- Local effect: Low testosterone levels can reduce sensitivity and readiness to respond, making erections less frequent or less robust.
Other hormones
- Thyroid hormones: Underactive or overactive thyroid function can affect libido and erectile capacity.
- Prolactin: Elevated levels (e.g. due to a prolactinoma) lower libido and can cause erectile problems.
- Insulin / metabolic hormones: Diabetes and metabolic disorders damage nerves and blood vessels and are a common cause of erectile dysfunction.
Testosterone deficiency in midlife (andropause) — symptoms and diagnosis
As men age, testosterone levels slowly decline in many cases. Typical symptoms of clinically relevant testosterone deficiency include:
- Reduced libido
- Erectile difficulties (especially fewer spontaneous erections)
- Fatigue, lack of drive
- Muscle loss, increased body fat
- Mood swings, depressive moods
- Reduced bone density
Important for diagnosis:
- Measuring total testosterone in the morning (before 10 a.m.) — ideally on several occasions.
- If values are borderline, also check free testosterone and SHBG (binding globulin).
- Clarify the cause (e.g. pituitary dysfunction, medication side effects, chronic illnesses).
Testosterone replacement: benefits, forms, and risks
If a clinically relevant deficiency is diagnosed (symptoms plus confirmed low levels), testosterone therapy can make sense. The goals are to improve libido, mood, body composition, and in some cases erectile function.
Dosage forms
- Transdermal gels or patches
- Intramuscular injections (short- or long-acting)
- Subcutaneous implants
Important during therapy
- Before starting, rule out prostate disease and establish a PSA baseline.
- Regular monitoring of testosterone levels, hematocrit (risk of polycythemia), liver values, and PSA.
- Contraindications: known prostate cancer, severe heart failure, and untreated severe sleep apnea syndrome (risks must be weighed individually).
- Effects on erections can vary — for vascular causes alone, TRT is not always sufficient; often a combination with vascular therapy, PDE5 inhibitors, or lifestyle measures is needed.
Arginine, citrulline: NO precursors and their significance
L-arginine is the amino acid precursor for the formation of nitric oxide (NO) via NO synthase. L-citrulline is converted into arginine in the body and can improve arginine availability over the long term. These amino acids are available over the counter as dietary supplements.
- Effect: Higher arginine levels can lead to more NO being produced, which supports blood vessel relaxation — theoretically beneficial for erections.
- Evidence: For some men with mild erectile dysfunction, L-arginine (often 3–6 g/day) or L-citrulline (commonly 1–3 g/day) shows moderate improvements.
- Safety: Usually well tolerated; side effects may include gastrointestinal discomfort. Caution is advised when taking nitrates at the same time (risk of a severe drop in blood pressure) and possibly with blood pressure medications.
Conclusion: Arginine/citrulline can be a complementary option, but they are not a reliable alternative to established treatments for moderate to severe erectile dysfunction.
Importance of ejaculations — physiological and possible health aspects
Ejaculation is part of normal sexual function. It has several physical and psychological relevance points:
- Reproductive function: Obviously necessary for conception; sperm quality depends on many factors such as age, health status, and ejaculation frequency.
- Prostate health: Observational studies suggest that more frequent ejaculation may be associated with a lower risk of prostate cancer on average. However, causal relationships have not been definitively proven.
- Psychological well-being: Regular sexual activity and satisfaction can reduce stress, promote sleep, and strengthen the relationship.
- Physiological "regulation": Ejaculations ensure the regular replacement of seminal fluid; very long periods of abstinence do not directly impair erectile mechanics, but may become relevant psychologically or in partner contact.
Practical tips: what you can do
- If you have erection problems, start with medical evaluation: cardiovascular risk, diabetes, hormone status.
- Lifestyle optimization: weight control, regular exercise, a healthy diet, quitting smoking, and moderate alcohol consumption improve vascular health and sexual function.
- If testosterone deficiency is suspected: blood tests in the morning, clarify the cause, and discuss treatment options with a specialist if deficiency is confirmed.
- Arginine/citrulline can be tried as an addition, but: watch for interactions (especially with nitrates) and keep expectations moderate.
- Communication with your partner and psychological support for performance anxiety or relationship problems can be crucial.
When should you see a specialist?
- For persistent erection problems, especially if they occur suddenly or are accompanied by chest pain/shortness of breath.
- If symptoms of testosterone deficiency (reduced libido, fatigue, muscle loss) are present — blood tests with your family doctor or an endocrinologist/urologist.
- If you have side effects or concerns about testosterone therapy or supplements.
