Declining testicular function with age: Hormonal and clinical correlates

Abstract

Testicular endocrine function and androgen-dependent secondary sexual characteristics were assessed in 283 men 18 to 96 years of age. Mean serum total testosterone levels remained unchanged up to age 70 and declined thereafter. In 29 per cent of the men over 70 years of age total testosterone levels were below the lower limit of normal for young adults, In contrast, mean free or unbound testosterone levels declined after age 50 and were below the lower limit of normal for young adults in 40 per cent of the men over 70 years of age. Serum-luteinizing hormone and follicle-stimulating hormone levels showed a slight but steady rise after age 40 which became more abrupt after age 70. Serum gonadotropin levels were elevated in approximately 60 per cent of the men over 70 years of age. Mean testis length and volume were decreased in 78 per cent and 37 per cent, respectively, of the men over 60 years of age. Facial, pubic and axillary hair were also reduced in amount whereas the prostate was enlarged in 73 per cent of the elderly men. There appeared to be an inverse relationship in older men between testicular size and gonadotropin levels, and a direct relationship between testicular and prostatic sizes. It would appear that some degree of Leydig cell hypofunction commonly begins at around 45 to 50 years of age, becoming more pronounced after age 70. The concomitant elevation in serum gonadotropin levels at this time indicates that this is due to a primary decline in testicular function and is not secondary to pituitary hypofunction.