Loss of Circadian Rhythmicity in Blood Testosterone Levels with Aging in Normal Men*

Abstract

Previous studies concerning the relationship of serum testosterone levels to aging in normal men have yielded apparently inconsistent results. Studies performing blood sampling in the morning have often shown an age-related decrease in testosterone levels, while those using afternoon samples have failed to show such a decrease. These results suggested to us the possibility that the circadian rhythm in serum testosterone levels might be altered with normal aging in men. Hourly blood samples were obtained for 24 h from 1 young (mean age, 52.2 yr) and 12 old (mean age, 17 yr) healthy men. Total testosterone levels were measured by RIA. The circadian rhythm in serum testosterone levels found in normal young men was markedly attenuated or absent in healthy elderly men; the early morning rise in testosterone levels characteristic of young men was not present in old age. Mean testosterone levels for the entire 24-h day were lower in healthy old men than in young men. These results demonstrate a clear decrease in serum testosterone levels in healthy old men compared to those in young men and provide an explanation for the inability to demonstrate an age-related decline in testosterone levels in earlier studies using serum samples obtained in the afternoon.

Changes in BMI modulate age-associated changes in sex hormone binding globulin and total testosterone, but not bioavailable testosterone in young adult men: the CARDIA Male Hormone Study

“…This is particularly important because the diurnal variation in testosterone appears to be suppressed in older men compared to younger men. 27 Further research is warranted to understand whether there are differential effects of BMI on this variation. Additionally, small volume of serum (approximately 0.5 ml) available for this study precluded the direct measurement of bioavailable testosterone.…”

Age-related changes in neuroendocrine rhythmic function in the rhesus macaque

“…Because leptin is generally associated with suppression of appetite, it also makes biological sense for its peak to occur at night, when diurnal species usually sleep. Similarly, plasma testosterone shows a nocturnal peak in both men and male rhesus macaques (Bremner et al 1983;Tenover et al 1988;Cooke et al 1993;Downs et al 2004;Garyfallou et al 2005;Schlatt et al 2008;Sitzmann et al 2010). Note that because of the underlying pulsatile pattern of its release (Tenover et al 1988;Plant and Witchel 2006), circulating testosterone levels display ultradian fluctuations as well as a 24-h pattern (Fig.…”

Impact of Aging on Steroid Hormone Biosynthesis and Secretion

“…As early as 50-60 years ago it was realized that aging is accompanied by significant reduction in testosterone levels [97,98]. Although some follow-up studies failed to detect age-related decline in plasma testosterone levels in older men [99][100][101][102][103][104], subsequent population-based cross-sectional and longitudinal studies have confirmed progressive loss of testosterone with aging in healthy men [96,[105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121][122]. Mirroring this decline in plasma testosterone concentration is an age associated increase in sex-hormonebinding globulin (SHBG) level [117], a major plasma carrier of testosterone, resulting in even more dramatic decreases in unbound free testosterone [110,[123][124][125], and weakly bound bioavailable testosterone [126,127].…”