Longitudinal Effects of Aging on Serum Total and Free Testosterone Levels in Healthy Me... - 0 views
press.endocrine.org/...jcem.86.2.7219
low t low Testosterone Testosterone SHBG FAI free androgen index male hormone hormones aging obesity
shared by Nathan Goodyear on 30 Mar 15
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NUMEROUS CROSS-SECTIONAL INVESTIGATIONS have demonstrated lower concentrations of circulating testosterone (T) and/or free T in older men
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T levels decline at a more or less constant rate, with age, in men, with no period of accelerated decline
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aging in men is associated with decreases in bone mineral density (BMD) (18, 19), lean body and muscle mass
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strength (22, 23) and aerobic capacity (24), as well as with increases in total and abdominal body fat, low-density lipoprotein cholesterol, and/or low-density lipoprotein/high-density lipoprotein cholesterol ratios (25, 26, 27, 28), all of which also occur in nonelderly hypogonadal men
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Most (1, 5, 6, 7, 8, 9), but not all (10, 11, 12), cross-sectional studies have demonstrated a decrease, with age, in total T in men
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total T, but not free T index, tended to decrease with greater BMI is consistent with prior studies showing that obesity is associated with decreases in both SHBG and total T, with an unchanged T-to-SHBG ratio
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The conventional definition for T levels is statistical (values more than 2 sd below the mean), rather than functional. Such a definition does not reflect clinical realities, such as the existence of characteristic individual set points for circulating hormone levels, below which one, but not another, individual may develop metabolic changes of hormone deficiency; nor does it address the concept of reserve capacity, the possibility that persons with hormone levels 2 sd below the population mean still may have adequate hormone concentrations to meet their metabolic needs.
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both T and free T index (a calculated value related to free or bioavailable T) decreased progressively at a rate that did not vary significantly with age, from the third to the ninth decades.
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contrasts with other studies showing diminished free, as well as total, T in with increasing total (48) or abdominal (49) obesity in men.
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Our analysis of date-adjusted T and free T index levels, by decade, showed that relatively high numbers of older men in this generally healthy population had at least one hypogonadal value (defined as below the 2.5th percentile for young men)
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The issue of how properly to define hypogonadism, or indeed any hormone deficiency, remains problematic
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The decrease in free T index was somewhat steeper than that of total T, owing to a trend for an increase in SHBG with age
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It would clearly be better to define the lower limit of normal for a hormone as: the blood level at which metabolic and/or clinical sequelae of hormone deficiency begin to appear, or the level below which definite benefits can be demonstrated for hormone supplementation for a significant proportion of the population
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an effect of aging to lower both total and bioavailable circulating T levels at a relatively constant rate, independent of obesity, illness, medications, cigarette smoking, or alcohol intake
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Article highlights the problems with the definition of low T. This article finds consistent decline in Total Testosterone and FAI with increasing age groups, with a significant portion of men > 60 meeting the required levels for "low T". This study found a decrease in total T and FAI at a consistent rate independent of variables, such as BMI. This study did find a decrease in SHBG and total T with obesity; in contrast to other studies.