Longitudinal effects of aging on serum total and free testosterone levels in healthy men. Baltimore Longitudinal Study of Aging.
Many studies have shown cross-sectional (and two small studies, longitudinal) declines in total and/or free testosterone (T) levels, with age, in men. The extent to which decline in T is the result of the aging process per se, as opposed to chronic illness, medication use, and other age-related factors, remains controversial. The frequency with which aging leads to T levels consistent with hypogonadism has also not been defined. These issues bear on the potential use of T replacement in aging men, because aging and hypogonadism have, in common, reduced bone and lean body mass and muscle strength and increased total and abdominal fat. We measured T and sex hormone-binding globulin (SHBG), by RIA, in stored samples from 890 men in the Baltimore Longitudinal Study on Aging. Using a mixed-effects model, we found independent effects of age and date of sampling to reduce T levels. After compensating for date effects, which investigation suggested was artifactual, we observed significant, independent, age-invariant, longitudinal effects of age on both T and free T index (free T index = T/SHBG), with an average change of -0.124 nmol/L.yr and -0.0049 nmol T/nmol SHBG.yr. T, but not free T index, also decreased with increasing body mass index. Use of beta-blocking drugs was associated with higher T and higher free T index levels. Using total T criteria, incidence of hypogonadal T levels increased to about 20% of men over 60, 30% over 70 and 50% over 80 yr of age, and even greater percentages when free T index criteria were employed. Our observations of health factor independent, age-related longitudinal decreases in T and free T, resulting in a high frequency of hypogonadal values, suggest that further investigation of T replacement in aged men, perhaps targeted to those with the lowest serum T concentrations, are justified.
Harman
S M
SM
The Intramural Research Program, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224, USA. harman@kronofoundation.org
Metter
E J
EJ
Tobin
J D
JD
Pearson
J
J
Blackman
M R
MR
D000328:Adult; D000375:Aging / Q000097:blood*; D015142:Baltimore; D006801:Humans; D007006:Hypogonadism / Q000097:blood / Q000453:epidemiology; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D011863:Radioimmunoassay; D012044:Regression Analysis; D015203:Reproducibility of Results; D012738:Sex Hormone-Binding Globulin / Q000032:analysis*; D012923:Social Class; D013739:Testosterone / Q000097:blood*; D044465:White People
D012738:Sex Hormone-Binding Globulin; D013739:Testosterone