Androgens in Health and Disease.pdf - E Library

350 Tenover
Table 1
Changes in Androgen Target Organs with Normal Aging
and with T Replacement in Young Hypogonadal Men
Young adult hypogonadal men
Target organ Changes seen with aging Pre-T a With T treatment
Muscle mass ↓ ↓ ↑
Muscle strength ↓ ↓ ↑
Fat mass ↑ ↑ ↓
Bone mineral density ↓ ↓ ↑
Libido ↓ ↓ ↑
Erectile function ↓ ↓ ↑
Sense of well-being or mood ↔/↓ ↓ ↑
a Compared to age-matched eugonadal men; ↓: decreased; ↑: increased; ↔: no change.
AGE-RELATED CHANGES IN ANDROGEN TARGET ORGANS
Androgens are known to have a variety of important physiologic actions, including
effects on muscle, bone, mood, prostate, bone marrow, cognitive function, and sexual
function. In hypogonadal young men who are replaced with T, changes in these various
areas have been reported (see Table 1). Declining lean body mass and strength, increased
fat mass, declining bone mineral density (BMD), decreased libido and potency, a decline
in general sense of well-being, and increased irritability are associated in variable degrees
with male aging (see Table 1).
Muscle and Fat
Sarcopenia, the loss of muscle mass, is an important finding with aging. The cumulative
decline in lean body mass, predominantly muscle mass, with age is about 35–40%
between the ages of 20 and 80 yr (33,34). This loss of muscle mass results predominantly
from a decrease in the number of type II, fast twitch fibers important for production of
power (35). In healthy older people, there is a strong correlation between muscle mass
and muscle strength (36), but the causes of the decline in muscle mass and strength with
age are probably multifactorial. Decreased muscle strength can lead to decreased physical
function (37). Androgens have long been known for their anabolic effects, and
physiological replacement of T in hypogonadal young men (38) or supraphysiological
treatment of eugonadal young men (39) has been shown to result in increases in lean body
mass, muscle size, and strength.
As muscle mass declines with age, body weight remains relatively constant, because
fat mass increases (40). Much of this is intra-abdominal fat, which has metabolic and
clinical implications (41). Independent of age, abdominal fat mass has been shown to
correlate inversely with serum free-T levels (42,43).
Bone
Male osteoporosis is becoming an important clinical entity as the life-span of men
increases (44). After age 60 yr, hip fracture rates in men increase dramatically, doubling
each decade (45). Mortality after hip fracture is higher in men than in women (46). Both