Sj. Winters et al., Testosterone, sex hormone-binding globulin, and body composition in young adult African American and Caucasian men, METABOLISM, 50(10), 2001, pp. 1242-1247
This study examined the diurnal variation in circulating total and free tes
tosterone and sex hormone-binding globulin (SHBG) levels in young adult Afr
ican American and Caucasian men in order to investigate whether there are d
ifferences in the secretion of these plasma hormones in populations at diff
erent risks of developing prostate cancer as they age. A significant and si
milar diurnal rhythm for total and free testosterone was found for both gro
ups. Serum levels of total testosterone were 29.4% and 23.9% lower at 8:00
Pm than at 8:00 AM in African American and Caucasian men, respectively. Sig
nificantly higher serum levels of total testosterone (P < .01) and SHBG (P
< .02) were found in the African American than in the Caucasian men in both
the morning and evening, whereas free testosterone levels were similar in
both groups. The higher SHBG levels appear to have an environmental/metabol
ic basis in that the waist circumference, waist-to-hip ratio, and fasting i
nsulin concentration were lower (P < .05) in African Americans than in Cauc
asians. In summary, these data indicate that racial differences in central
adiposity in men are established in early adulthood and influence circulati
ng SHBG and thereby testosterone levels. In light of the findings by others
that SHBG increases cyclic adenosine monophosphate (cAMP) production in th
e prostate and that cAMP-dependent protein kinase A is a coactivator of the
androgen receptor, these studies provide a possible mechanism by which cir
culating androgens may contribute to the increased risk for prostate cancer
among African American men. Copyright (C) 2001 by W.B. Saunders Company.