What causes semen volume to decrease in men over 40?
Executive summary
Semen volume commonly declines with age and the change becomes more noticeable after the late 30s to 40s, driven by a mix of physiological aging, glandular and structural changes, hormonal shifts, nerve decline, medications and lifestyle factors [1] [2] [3]. Determining the cause requires distinguishing true hypospermia from temporary fluctuation and then investigating seminal-vesicle/prostate contribution, ejaculatory mechanics, endocrine status and reversible contributors such as drugs or infections [4] [5] [6].
1. Age and the baseline decline in semen volume
Multiple large studies and reviews report that key semen parameters including volume, motility and DNA integrity decline with age, with measurable decreases beginning in the mid‑30s and more pronounced effects in men over 40 [1] [7]. Clinical summaries and patient-facing guides note that men over 50 typically have lower semen volumes compared with younger men, and clinicians treat age as a common, non‑pathologic contributor to weaker ejaculations and reduced ejaculate volume [3] [8].
2. The glands that make most of the fluid — seminal vesicles and prostate
Because roughly two‑thirds of ejaculate volume derives from the seminal vesicles and about one‑third from the prostate, damage or dysfunction in these glands—congenital absence, infection, inflammation or surgical injury—directly reduces semen volume [4] [6]. Seminal vesicle atrophy, ejaculatory duct obstruction or congenital absence of the vas deferens can produce markedly low volumes or near‑absence of semen and therefore are primary structural causes to consider [4] [6].
3. Hormonal and systemic disease influences
Endocrine changes with aging—most notably declining testosterone—can reduce secretions from reproductive glands and lower ejaculate volume, and other systemic diseases such as thyrotoxicosis or diabetes can alter semen quantity and quality through hormonal or metabolic effects [9] [5] [6]. Professional sources link low testosterone to reduced seminal gland function and note that excess thyroid hormone and other endocrine disorders associate with abnormalities that include reduced semen volume [9] [5].
4. Nerves, ejaculation mechanics, retrograde ejaculation and surgery
Age‑related deterioration of nerve fibers and pelvic floor muscle function can weaken the contractions that expel semen, producing less forceful ejaculation and smaller volume; neurological disease or damage from surgery can have the same effect [2] [5]. Retrograde ejaculation—when semen flows into the bladder instead of out the urethra—can mimic low external volume and is linked to nerve injury, diabetes, certain medications and bladder‑neck dysfunction [5] [8].
5. Medications, infections, trauma and lifestyle contributors
A wide array of commonly used drugs (antihypertensives, alpha‑blockers and others), prior pelvic surgery, infections such as prostatitis or epididymitis, and genital or pelvic trauma can lower semen volume or block its exit [5] [10] [11]. Lifestyle factors and chronic conditions—including smoking, obesity, heavy alcohol use and metabolic disease—are repeatedly cited as detrimental to ejaculatory volume and overall semen quality, and they are often at least partially reversible with modification [8] [11] [6].
6. Putting it together: evaluation and realistic expectations
Guides for clinicians recommend confirming low volume on repeated semen analyses, assessing medical and surgical history, performing hormonal testing and imaging to look for obstruction or glandular absence, and considering reversible contributors such as drugs or infections before labeling age as the sole cause [5] [4] [6]. Because aging is a common backdrop, some decline may be inevitable, but many specific causes—blockage, infection, medication effects, endocrine disorders and some surgical problems—are potentially treatable once identified [4] [11] [6].