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Human Reproduction Vol.17, No.12 pp. 3251–3253, 2002
Population variation in age-related decline in male salivary
testosterone
Peter T.Ellison
1,7
, Richard G.Bribiescas
2
, Gillian R.Bentley
3
, Benjamin C.Campbell
4
,
Susan F.Lipson
1
, Catherine Panter-Brick
5
and Kim Hill
6
1
Department of Anthropology, Harvard University, Cambridge, MA,
2
Department of Anthropology, Yale University, New Haven, CT,
USA,
3
Department of Anthropology, University College London, London, UK,
4
Department of Anthropology, Boston University,
Boston, MA, USA,
5
Department of Anthropology, Durham University, Durham, UK and
6
Department of Anthropology, University of
New Mexico, Albuquerque, NM, USA
7
To whom correspondence should be addressed at: Department of Anthropology, Peabody Museum, Harvard University,
11 Divinity Avenue, Cambridge, MA 02138 USA. E-mail: pellison@fas.harvard.edu
BACKGROUND: Age-related declines in free and bioavailable testosterone are frequently reported for Western
populations, but interpopulation variation in this pattern has not previously been investigated. METHODS: Salivary
testosterone was measured using a consistently applied protocol on morning samples collected from men in four
populations (USA, Congo, Nepal, and Paraguay) representing different geographical, ecological, and cultural
settings. RESULTS: Mean testosterone levels varied significantly between the four populations. The mean testosterone
differences between populations were greatest for young men (aged 15–30 years) and insignificant for older men
(aged 45–60 years). The slope of age-related decline in testosterone was significant in the USA and Congolese
participants, but not in the Nepalese or Paraguayan participants. CONCLUSIONS: Age patterns of testosterone
decline vary between populations primarily as a result of variation in the peak levels attained in young adulthood.
The potential consequences of this variation for other aspects of male health deserve investigation.
Key words: ageing/population variation/salivary testosterone/testosterone
Introduction
Although formerly controversial, an age-related decline in free
and bioavailable testosterone in healthy males is now a
frequently reported pattern in Western populations (Ferrini and
Barrett-Connor, 1998; Vermeulen et al., 1999; Harman et al.,
2001). Age-related declines in testosterone levels in males
have been associated with changes in body composition,
including increases in fat mass, decreases in muscle mass,
and decreases in bone mineral density (Denti et al., 1999;
Vermeulen et al., 1999; Kenny et al., 2000; van den Beld
et al., 2000). Reflecting these linkages to body composition,
age-related declines in male testosterone are also associated
with elevated risk of type II diabetes (Stellato et al., 2000;
Haffner et al., 1996), coronary heart disease (Simon et al.,
1997; De Pergola et al., 1997), ischemic stroke (Jeppesen
et al., 1996) and osteoporosis (Francis, 1999; Snyder et al.,
1999a). Low testosterone levels in older men are also
associated with low libido, erectile dysfunction, and depression
(Barrett-Connor et al., 1999; Schweiger et al., 1999; Wang
et al., 2000). On the other hand, high testosterone levels have
been associated with elevated risk and progress of prostate
cancer (Crawford, 1992; van Tinteren and Dasio, 1993).
Testosterone supplementation of older men has been shown to
result in increases in lean-body mass, decreases in fat mass,
© European Society of Human Reproduction and Embryology 3251
increases in bone mineral density, and improvements in mood
and sexual function (Bhasin and Tenover, 1997; Snyder et al.,
1999a,b; Winters, 1999).
Despite evidence of its clinical importance, relatively little
is known about population variation in age patterns of
testosterone. This contrasts strikingly with the increasing
awareness of population variation in female ovarian steroid
profiles and its relationship to disease risk (Ellison et al., 1993;
O’Rourke and Ellison, 1993; Ellison, 1999; Jasienska et al.,
2000; Jasienska and Thune, 2001). There are scattered reports
of male testosterone levels from non-Western, non-clinical
populations, but the comparability of these data is limited
by differences in sample collection, handling, and assay
procedures (Guerra-Garcia et al., 1969; Smith et al., 1975;
Christiansen, 1991a,b; Beall et al., 1992; Campbell, 1994).
This report presents data on age variation in male salivary
testosterone values from four populations spanning broad
genetic, ecological, and life style differences. All the samples
were collected using the same protocols and were assayed in
the same laboratory using consistent methods. The data are
used for a preliminary test of the hypothesis that significant
population variation exists in the pattern of age-related decline
in male testosterone. By analogy with findings for women
(Ellison et al., 1993), we expect that non-Western males will
P.T.Ellison et al.
Table I. Mean (pmol/l) salivary testosterone levels (T) from men in four populations, for total sample and for three age groups.
Population All ages 15 to ⬍30 years 30 to ⬍45 years 45–60 years
T (pmol) SEM n T (pmol) SEM n T (pmol) SEM n T (pmol/l) SE n
USA 259 10 106 335 20 24 288 17 31 238 14 26
Congo 268 12 33 286 15 17 250 19 11 247 34 5
Nepal 240 13 37 251 18 22 224 19 14 225 0 1
Paraguay 192 12 45 197 25 15 187 14 21 192 36 8
P-value 0.0002 0.0001 0.0004 NS
P-value is given for one-way ANOVA; NS ⫽ not significant.
have lower levels of testosterone in adulthood and slower rates
of decline in testosterone with increasing age.
Materials and methods
Participants in this study represent males from four populations that
are geographically, genetically, ecologically, and culturally distinct:
Lese horticulturalists from the Ituri Forest, Democratic Republic of
the Congo (formerly Zaı
¨
re), (Bentley et al., 1993; n ⫽ 33); Tamang
agropastoralists from central Nepal (n ⫽ 39; Ellison and Panter-
Brick, 1996); Ache foragers from southern Paraguay (Bribiescas,
1996; n ⫽ 45) and residents of Massachusetts, USA (n ⫽ 106). Lese,
Tamang, and Ache participants represent all available willing males
in the corresponding study areas. The USA participants were recruited
by public advertisement, thus the potential for self-selection bias
should be noted. Age data were derived from detailed demographic
interviews in the Congo, Nepal, and Paraguay and from self-report
in the USA.
In all cases participants provided between one and five morning
saliva samples collected within 2 h of waking from 1–5 days according
to established collection protocols which minimize the risk of contam-
ination with serum or gingival fluid (Lipson and Ellison, 1989). The
samples were preserved with sodium azide until they could be
transferred to the laboratory and frozen at –20°C. Testosterone levels
have been found to be stable under these collection and handling
procedures for up to 6 months (Lipson and Ellison, 1989). Testosterone
values were determined for each sample by a tritium-based radio-
immunoassay according to published protocols (Ellison et al., 1989).
The sample values for individual participants were averaged to
provide mean values for each subject.
The age pattern of testosterone within each population was analysed
using simple linear regression. Sample sizes were too small to justify
higher order curve fitting. Population variation in average testosterone
values is assessed by analysis of variance and by multiple linear
regression with age, population, and age multiplied by population
interaction as independent variables. For the purposes of the multiple
regression population was re-coded as a binary variable, USA and
non-USA.
Results
The mean salivary testosterone values for men in the four
populations were significantly different (ANOVA, P ⫽ 0.0002,
Table I) although they fall within the broad normal range
(100–1000 pmol/l) for adult males in all cases. However, the
differences are not consistent across age groups and show
convergence with age. Population differences are greatest
3252
among men under the age of 30 years (ANOVA, P ⫽ 0.0001)
and are non-significant for men 45–60 years.
A linear regression of testosterone on age for the combined
data from all four populations indicates a highly significant
negative relationship (y ⫽ 332 – 2.0x, P ⫽ 0.0001). The
individual population regressions of testosterone against age
are significant in the USA (y ⫽ 418 – 3.4x, P ⫽ 0.0001) and
Congo (y ⫽ 346 – 2.3x, P ⫽ 0.03), but not in Nepal (y ⫽
286 – 1.5x, P ⫽ 0.39) or Paraguay (y ⫽ 218 – 0.7x, P ⫽
0.50). A multiple linear regression model with age, population
(recoded as USA and non-USA), and age⫻population inter-
action as independent variables indicates significant effects of
all three variables (y ⫽ 549 – 5.2⫻Age – 131.5⫻Population
⫹ 1.7⫻Age⫻Population, multiple R ⫽ 0.47, P ⫽ 0.0001.
Significance of individual variables: Age, P ⫽ 0.0001; Popula-
tion, P ⫽ 0.0002; Age⫻Population, P ⫽ 0.05).
Discussion
The data presented here provide the first opportunity to consider
population variation in the relationship of male testosterone to
age. All the data were collected according to the same protocols
and analysed with the same assay methods in the same
laboratory. This common methodology helps to control for
many of the sources of variation that may confound the
comparison of results from different studies. The most import-
ant general observation from these data is that age-related
decline in free testosterone, as represented by salivary levels,
is not a uniform characteristic of all populations. In particular,
the rate of decline with age varies significantly between
populations and in some populations (i.e. Nepal and Paraguay)
does not achieve statistical significance, although this may be
due to the sample size limitations in this study.
The testosterone levels of older men (⬎45 years) tend to
converge for all the populations studied while the levels of
younger men (⬍30 years) vary significantly. This suggests
that variability in the pattern of testosterone decline with age,
results from population variation in the reproductive physiology
of young males rather than in population differences in the
rate of reproductive senescence among older males. If so,
research into the mechanisms underlying age patterns of male
testosterone should focus on the determinants of young adult
levels as well as the causes of age-related decline.
Because population differences in age patterns of testoster-
one have not previously been appreciated, the implications of
Interpopulation salivary testosterone variation in males
such variation for patterns of health risk have not been
considered. If, for example, set-points for muscle anabolism
and bone mineral density are established relative to testosterone
levels in young adulthood, a steeper decline in testosterone
from higher young-adult levels might result in more rapid age-
related changes in male body composition, bone mineral
density, and related health risks. Higher testosterone exposure
throughout adulthood in populations with high young-adult
levels may also lead to greater prostate cancer risk. These
possibilities provide additional motivation for increased efforts
to study global variation in male gonadal function to comple-
ment studies of Western populations.
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Submitted on March 7, 2002; resubmitted on June 11, 2002; accepted on July
31, 2002
