TESTOSTERONE LEVELS AMONG ACH] HUNTER-GATHERER MEN A Functional Interpretation of Population Variation among Adult Males
Richard G. Bribiescas
Harvard University
Salivary testosterone levels were m e a s u r e d in a p o p u l a t i o n of N e w World i n d i g e n o u s a d u l t hunter-gatherer m a l e s in order to compare circulating levels of free u n b o u n d bioactive steroid with those p r e v i o u s l y reported a m o n g Boston and n o n w e s t e r n males. The study p o p u l a t i o n consisted of adult Ach6 hunter-gatherer m a l e s (n = 45) living in eastern Paraguay. M o r n i n g and e v e n i n g salivary testosterone levels (Tsal A.M.; Tsal P.M.) a m o n g the Ach~ were c o n s i d e r a b l y lower than western v a l u e s (Boston) and even lower than other p r e v i o u s l y reported n o n w e s t e r n p o p ulations IEfe, Lese, Nepalese). N o association was o b s e r v e d b e t w e e n height, weight, or age and salivary testosterone levels w i t h i n the Ach6 group, although older men (ages > 40) were p o o r l y r e p r e s e n t e d in the s t u d y sample. Nevertheless, a m i l d correlation was o b s e r v e d b e t w e e n Ach4 Tsal A.M. levels and BMI (r = 0.133, p = 0.0725). C o m p a r i s o n of Ach~ values with those for other p o p u l a t i o n s confirms the p r e v a l e n c e of significant i n t e r p o p u l a t i o n a l variation in testosterone levels a m o n g a d u l t males. I n t e r p o p u l a t i o n a l variation in male testosterone is not as great, however, as has b e e n d o c u m e n t e d for o v a r i a n steroids a m o n g f e m a l e s , nor is it l i k e l y that such variation reflects differences in male fecundity. Nevertheless, such i n t e r p o p u l a t i o n a l variation in salivary testosterone
Received July 18, 1995; accepted September 6, 1995.
Address all correspondence to Richard G. Bribiescas, Department of Anthropology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138. E-mail: rgbrib@fas. harvard, edu Copyright 9 1996 by Walter de Gruyter, Inc., New Human Nature, Vol. 7, No. 2, pp. 163-188. 163
York
1045-6767/96/$1.00+.10
164
Human Nature, Vol. 7, No. 2, 1996
levels may have a functional significance in the regulation of protein anabolism in skeletal muscle, thereby affecting the overall energy budget of the organism. It is suggested that relative suppression of average testosterone may be adaptive under conditions of chronic energy shortage. KEYWORDS:Ach4; Hunter-gatherers; Muscle anabolism; Population variation; Salivary testosterone.
Anthropological field investigations in human female reproductive ecology have advanced compelling evidence outlining the adaptive response of human reproductive physiology to energetic stressors in the context of ecological pressures such as diet, workload, and disease (see Ellison 1994 for review). Moreover, salivary steroid hormone assays have proven to be invaluable tools of field studies among anthropological populations in remote and difficult locations due to the noninvasive nature of sample collection, the ability of saliva to be stored at ambient temperature, and the inherent correlation between salivary steroid concentrations and biologically active levels in serum (Ellison 1988; Lipson and Ellison 1989; Navarro et al. 1986, 1987). This relatively n e w methodological paradigm has generated a new understanding of populational variation in female reproductive hormone function as well as suggested a revised outlook on the ramifications of this variation. Among foraging, horticultural, agricultural, and urban women, it has been demonstrated that concentrations of reproductive steroids, such as progesterone and estradiol, vary significantly between populations, indicating that ovarian function is sensitive to such ecological variables as nutrition and workload (Ellison and Lager 1986; Ellison et al. 1986; Ellison, Peacock, and Lager 1989; Jasienska and Ellison 1993; PanterBrick et al. 1993). Hence, variation in ovarian endocrine function appears to be a valid reflection of female fecundity (Ellison et al. 1993). As a result of this growing evidence, human evolutionary biologists have reevaluated the significance of these potentially adaptive features of female reproductive function as well as their role in human evolution, demography, and present-day health issues (Eaton et al. 1994; Ellison 1990; Ellison et al. 1993). Despite these strides in female reproductive ecology, few investigations have focused on the evolutionary biology of h u m a n male gonadal function, particularly the range of h u m a n testosterone variability. While this deficit in our knowledge has been partially addressed by various anthropological investigations of nonwestern males, a large gap remains in our understanding of both the extent and the functional significance of observed variation in male hormone function b e t w e e n populations.
Testosterone Levels among Ach~ Males
165
In order to further our understanding of interpopulational variation in male hormone function, this investigation reports salivary testosterone levels among Ach6 hunter-gatherer males living in eastern Paraguay. A hypothesis regarding the functional significance of population variation in male testosterone levels is also advanced.
MATERIALS AND METHODS Subjects Ach6 subjects consisted of adult males that until recently lived as fulltime nomadic hunter-gatherers. A brief description of the ecological and residence patterns of the Northern Ach6 group is presented to document the ecological pressures that make them a representative nonwestern population. Since first peaceful contact in 1971, the Northern Ach6 have divided their time between missionary settlements and full-time foraging. In 1978, the Catholic colony of Chupa Pou was founded in the Canindeyu forest region of eastern Paraguay approximately 35 km north of Curuguaty near the Jejui Guasu River (Hill and Hawkes 1983). Chupa Pou consists of approximately 70 households (ca. 400 individuals), with occasional small fluctuations due to families and individuals moving between neighboring Ach6 communities. The Northern Ach6 at Chupa Pou are autonomous, owning approximately 800 hectares of land given to them by the Catholic church (Hill and Hurtado 1995). The community grows several crops such as corn and manioc; manioc is the most heavily cultivated since it is easiest to tend. Although horticultural products have become significant components of the Ach6's diet, meat and other forest products obtained through foraging still account for a substantial portion (Hawkes et al. 1987). Foraging trips into the surrounding forest may last days, weeks, or even several months with entire families engaging in full-time hunting and gathering. Time-allocation investigations by Hawkes and colleagues indicate that Ach6 men and w o m e n at Chupa Pou spend 25% and 22% of their time in the forest, respectively (Hawkes et al. 1987). Even w h e n individuals are residing in the colony, they subsist primarily on forest products, such as wild game, grubs, and wild fruits brought back by other individuals from the forest. Occasionally, food products are purchased from local Paraguayans although this is u n c o m m o n since these items are relatively expensive (Hawkes et al. 1987). It is important to note, however, that despite their reported daily high caloric intake (3,827 kcal/day), primarily in the form of meat during
166
Human Nature, Vol. 7, No. 2, 1996
foraging trips in the surrounding forests (Hill et al. 1984), the Northern Ach6 at Chupa Pou ingest significantly less meat when they are residing in the colony, which was the setting for this investigation (16-22% compared with 46% of total dietary caloric intake while in the forest) (Hawkes et al. 1987). Although this does not outline absolute differences in caloric intake, it is indicative of important dietary differences (see Hawkes et al. 1987 for a review). In addition, agricultural products contribute a marginal absolute number of calories to their diet due primarily to the poor crop return as a result of the lack of modern farming implements and methods as well as the poor quality of the sandy local soil (Hill and Hurtado 1995). Furthermore, although Chupa Pou was founded as a Catholic mission, dietary supplements and medical care are almost nonexistent. Although one or more Catholic priests usually reside at the colony, they are poorly trained to handle medical situations or to provide basic health care needs such as inoculations. Visits by Paraguayan government health care workers are infrequent and sporadic. The resulting conditions make pneumonia, gastrointestinal infections, and upper and lower respiratory illnesses commonplace, aggravated over time by open fires in poorly ventilated dirt-floor houses. As a consequence, during the past fifteen years of recorded demographic data, infant mortality as been and continues to be extremely high, with 20% of Northern Ach6 infants failing to reach their first birthday (Hill and Hurtado 1995).
Sample Collection Salivary samples were collected from 46 adult Ach~ males from Chupa Pou (ages 17-approximately 64, p~ = 35.82 --+ 11.84 SE) during July and August 1992. One male was deleted from the final sample due to identification error (final n -- 45). Ages of males younger than 20 years were determined by demographic data of exact year of birth whereas ages of males between 20 and 35 were determined by correlating life histories with known events. Older males (>35 years) were aged by more complicated methods of cross-referencing (Hill and Hurtado 1995). Males w h o reportedly suffered from chronic illnesses such as tuberculosis were excluded from the study as well as those w h o were acutely ill (e.g., colds, pneumonia). Men were recruited randomly in exchange for a communal gift. Subjects were given two 12 x 75 mm polystyrene tubes daily and instructed to collect saliva twice each day, once immediately after waking and once at sunset. Instructions were given verbally in Ach6 and reinforced daily to maximize collection consistency. Variation d u e to individuals having different wake times was minimal since all Ach6
Testosterone Levels among Ach~ Males
167
usually awoke at sunrise and returned from their fields or from the forest at sunset with regularity. Sugarless gum was used as a salivary stimulant. Upon collection, filled tubes were treated with sodium azide (NAN3) to prevent bacterial or fungal contamination. The number of collection days per individual ranged from 1 to 10 (Ix = 5.3). Samples were stored at ambient temperature (ca. 20~ until they were transported to Harvard University where they were immediately placed in frozen storage (-4~ These procedures have previously been validated by Lipson and Ellison (1989).
Assay Procedures Assay procedures follow those of Ellison and colleagues (1988). Salivary samples were thawed and centrifuged for 10 minutes at 3,000 r.p.m, to precipitate proteins and/or mucopolysaccharides. Salivary aliquots of 1.0 ml were pipetted into 18 • 175 mm glass tubes with 100 ~l of tritiated testosterone recovery counts (1,000 cpm/100 ixl) added to quantify extraction efficiency. Aliquots were then extracted by adding 5.0 ml anhydrous ethyl ether and vortexing for 2 minutes. Salivary samples and ether were allowed to separate and then placed in frozen CO 2. Upon freezing of the aqueous saliva, supernatant ether was poured into individual 16 x 100 glass tubes which were then placed under a gentle stream of N 2 and dried in a block heater. The extraction procedure was repeated with the resulting dried residues reconstituted using 1.0 ml of phosphate-gel buffer. Duplicate 400 ;xl aliquots of reconstituted sample were subsequently assayed using a specific antiserum (GDN #250 obtained from G. Niswender, Colorado State University) and a fourposition tritiated testosterone competitor (Amersham Corp., Arlington Heights, IL). Following an overnight incubation at 4~ antibody b o u n d and unbound steroids were separated using dextran-coated charcoal. Scintillation fluid was then added to the b o u n d steroid fraction and measured for beta emissions.
Statistical Analyses Standard descriptive statistics such as means, standard deviations (SD), and standard errors (SE) were calculated for both morning and evening Ach6 salivary testosterone levels. Diurnal patterns of Ach6 salivary testosterone were analyzed using paired t-tests after log transformation of raw values to normalize distributions. Log-transformed interpopulational testosterone levels (Northern Ach6 vs. Efe, Lese, Nepalese) were also analyzed using unpaired, two-tailed t-tests. Previous researchers have cautioned against interpreting interpopulational salivary steroid differences due to possible inter-laboratory variance (Read
168
Human Nature, Vol. 7, No. 2, 1996
1993); however, all of the salivary testosterone values for each of these populations were determined in the same laboratory using identical protocols. Correlations between morning and evening salivary testosterone levels and age, height, weight, and BMI among Ach6 males were calculated using Pearson's product-moment coefficient of correlation on log-transformed data to normalize the distributions and d a m p e n outliers. Results were considered significant at the 0.05 level.
RESULTS Assay Variability Inter-assay variability for Ach6 samples was measured using three separate quality control pools yielding the following results: high pool (~ = 5.34%); medium pool (~ = 5.62%); low pool (.. = 6.27%). Intraassay variability assessed at the 50% binding point (ED 50) of the standard curve was 5.57%.
Salivary Testosterone Levels Ach6 morning salivary testosterone levels are shown in Table 1. Average morning salivary testosterone among Ach6 males was 192 + 12.2 SE pmol/L, with evening salivary testosterone exhibiting a mean of 156 +11.4 SE pmol/L. Diurnal effects among Ach6 males were clearly evident, with 88.8% of subjects demonstrating significantly higher mean morning salivary testosterone in comparison to evening values. As a group, morning salivary testosterone samples were significantly higher than evening samples (paired t = -11.088, d.f. = 89, p < 0.0001), indicative of circadian rhythms observed in other populations (Table 1). No statistically significant relationships were observed b e t w e e n either morning or evening salivary testosterone levels and any of the predefined anthropometric measures--height, weight, or body mass index (BMI). However, with the exclusion of one outlier, a mild positive correlation was Average Morning and Evening Salivary Testosterone values (pmol/L) among Ach6 Males
Table 1.
Morning
Evening
N
Mean
SD
SE
Mean
SD
SE
45
192
81.5
12.2
156
76.7
11.4
3"I
] .9
y=0.016X+ 1.797 r=0.133
2.5.1 o ~
)o
1
.9
$
1.5-
o
:
o
0
o o 1
I
I
I
I
I
20
22.5
25
27.5
30
32.5
0
Log of AM Salivary Testosterone (pmol/L)
BMI
Figure I
Scattergram of average m o r n i n g salivary testosterone; regression with body mass index (BMI) for Ach~ males. 800
-
600 -
[]
AMT~•
[]
PMTsal+ 1.0SE
T %*,.,
o
400 -
T v',.
T
T ,_-i-_,|
%. :.T.T.:m
~
200 -
~,. ~
-- i~]
T
:,:.:,:!
~-~, :';';';i x x :;:::,'! x .. "'":'! k k ~.-C.-'.m \ \ :':+!
0 Boston
Lese
Efe
Nepal
Ache
Population
Figure 2.
Bar graph of average m o r n i n g a n d e v e n i n g salivary testosterone levels a m o n g Ach6, Efe, Lese, a n d Nepal males. 169
H u m a n Nature, Vol. 7, No. 2, 1996
170 t~
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Richard G. Bribiescas
Harvard University
Salivary testosterone levels were m e a s u r e d in a p o p u l a t i o n of N e w World i n d i g e n o u s a d u l t hunter-gatherer m a l e s in order to compare circulating levels of free u n b o u n d bioactive steroid with those p r e v i o u s l y reported a m o n g Boston and n o n w e s t e r n males. The study p o p u l a t i o n consisted of adult Ach6 hunter-gatherer m a l e s (n = 45) living in eastern Paraguay. M o r n i n g and e v e n i n g salivary testosterone levels (Tsal A.M.; Tsal P.M.) a m o n g the Ach~ were c o n s i d e r a b l y lower than western v a l u e s (Boston) and even lower than other p r e v i o u s l y reported n o n w e s t e r n p o p ulations IEfe, Lese, Nepalese). N o association was o b s e r v e d b e t w e e n height, weight, or age and salivary testosterone levels w i t h i n the Ach6 group, although older men (ages > 40) were p o o r l y r e p r e s e n t e d in the s t u d y sample. Nevertheless, a m i l d correlation was o b s e r v e d b e t w e e n Ach4 Tsal A.M. levels and BMI (r = 0.133, p = 0.0725). C o m p a r i s o n of Ach~ values with those for other p o p u l a t i o n s confirms the p r e v a l e n c e of significant i n t e r p o p u l a t i o n a l variation in testosterone levels a m o n g a d u l t males. I n t e r p o p u l a t i o n a l variation in male testosterone is not as great, however, as has b e e n d o c u m e n t e d for o v a r i a n steroids a m o n g f e m a l e s , nor is it l i k e l y that such variation reflects differences in male fecundity. Nevertheless, such i n t e r p o p u l a t i o n a l variation in salivary testosterone
Received July 18, 1995; accepted September 6, 1995.
Address all correspondence to Richard G. Bribiescas, Department of Anthropology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138. E-mail: rgbrib@fas. harvard, edu Copyright 9 1996 by Walter de Gruyter, Inc., New Human Nature, Vol. 7, No. 2, pp. 163-188. 163
York
1045-6767/96/$1.00+.10
164
Human Nature, Vol. 7, No. 2, 1996
levels may have a functional significance in the regulation of protein anabolism in skeletal muscle, thereby affecting the overall energy budget of the organism. It is suggested that relative suppression of average testosterone may be adaptive under conditions of chronic energy shortage. KEYWORDS:Ach4; Hunter-gatherers; Muscle anabolism; Population variation; Salivary testosterone.
Anthropological field investigations in human female reproductive ecology have advanced compelling evidence outlining the adaptive response of human reproductive physiology to energetic stressors in the context of ecological pressures such as diet, workload, and disease (see Ellison 1994 for review). Moreover, salivary steroid hormone assays have proven to be invaluable tools of field studies among anthropological populations in remote and difficult locations due to the noninvasive nature of sample collection, the ability of saliva to be stored at ambient temperature, and the inherent correlation between salivary steroid concentrations and biologically active levels in serum (Ellison 1988; Lipson and Ellison 1989; Navarro et al. 1986, 1987). This relatively n e w methodological paradigm has generated a new understanding of populational variation in female reproductive hormone function as well as suggested a revised outlook on the ramifications of this variation. Among foraging, horticultural, agricultural, and urban women, it has been demonstrated that concentrations of reproductive steroids, such as progesterone and estradiol, vary significantly between populations, indicating that ovarian function is sensitive to such ecological variables as nutrition and workload (Ellison and Lager 1986; Ellison et al. 1986; Ellison, Peacock, and Lager 1989; Jasienska and Ellison 1993; PanterBrick et al. 1993). Hence, variation in ovarian endocrine function appears to be a valid reflection of female fecundity (Ellison et al. 1993). As a result of this growing evidence, human evolutionary biologists have reevaluated the significance of these potentially adaptive features of female reproductive function as well as their role in human evolution, demography, and present-day health issues (Eaton et al. 1994; Ellison 1990; Ellison et al. 1993). Despite these strides in female reproductive ecology, few investigations have focused on the evolutionary biology of h u m a n male gonadal function, particularly the range of h u m a n testosterone variability. While this deficit in our knowledge has been partially addressed by various anthropological investigations of nonwestern males, a large gap remains in our understanding of both the extent and the functional significance of observed variation in male hormone function b e t w e e n populations.
Testosterone Levels among Ach~ Males
165
In order to further our understanding of interpopulational variation in male hormone function, this investigation reports salivary testosterone levels among Ach6 hunter-gatherer males living in eastern Paraguay. A hypothesis regarding the functional significance of population variation in male testosterone levels is also advanced.
MATERIALS AND METHODS Subjects Ach6 subjects consisted of adult males that until recently lived as fulltime nomadic hunter-gatherers. A brief description of the ecological and residence patterns of the Northern Ach6 group is presented to document the ecological pressures that make them a representative nonwestern population. Since first peaceful contact in 1971, the Northern Ach6 have divided their time between missionary settlements and full-time foraging. In 1978, the Catholic colony of Chupa Pou was founded in the Canindeyu forest region of eastern Paraguay approximately 35 km north of Curuguaty near the Jejui Guasu River (Hill and Hawkes 1983). Chupa Pou consists of approximately 70 households (ca. 400 individuals), with occasional small fluctuations due to families and individuals moving between neighboring Ach6 communities. The Northern Ach6 at Chupa Pou are autonomous, owning approximately 800 hectares of land given to them by the Catholic church (Hill and Hurtado 1995). The community grows several crops such as corn and manioc; manioc is the most heavily cultivated since it is easiest to tend. Although horticultural products have become significant components of the Ach6's diet, meat and other forest products obtained through foraging still account for a substantial portion (Hawkes et al. 1987). Foraging trips into the surrounding forest may last days, weeks, or even several months with entire families engaging in full-time hunting and gathering. Time-allocation investigations by Hawkes and colleagues indicate that Ach6 men and w o m e n at Chupa Pou spend 25% and 22% of their time in the forest, respectively (Hawkes et al. 1987). Even w h e n individuals are residing in the colony, they subsist primarily on forest products, such as wild game, grubs, and wild fruits brought back by other individuals from the forest. Occasionally, food products are purchased from local Paraguayans although this is u n c o m m o n since these items are relatively expensive (Hawkes et al. 1987). It is important to note, however, that despite their reported daily high caloric intake (3,827 kcal/day), primarily in the form of meat during
166
Human Nature, Vol. 7, No. 2, 1996
foraging trips in the surrounding forests (Hill et al. 1984), the Northern Ach6 at Chupa Pou ingest significantly less meat when they are residing in the colony, which was the setting for this investigation (16-22% compared with 46% of total dietary caloric intake while in the forest) (Hawkes et al. 1987). Although this does not outline absolute differences in caloric intake, it is indicative of important dietary differences (see Hawkes et al. 1987 for a review). In addition, agricultural products contribute a marginal absolute number of calories to their diet due primarily to the poor crop return as a result of the lack of modern farming implements and methods as well as the poor quality of the sandy local soil (Hill and Hurtado 1995). Furthermore, although Chupa Pou was founded as a Catholic mission, dietary supplements and medical care are almost nonexistent. Although one or more Catholic priests usually reside at the colony, they are poorly trained to handle medical situations or to provide basic health care needs such as inoculations. Visits by Paraguayan government health care workers are infrequent and sporadic. The resulting conditions make pneumonia, gastrointestinal infections, and upper and lower respiratory illnesses commonplace, aggravated over time by open fires in poorly ventilated dirt-floor houses. As a consequence, during the past fifteen years of recorded demographic data, infant mortality as been and continues to be extremely high, with 20% of Northern Ach6 infants failing to reach their first birthday (Hill and Hurtado 1995).
Sample Collection Salivary samples were collected from 46 adult Ach~ males from Chupa Pou (ages 17-approximately 64, p~ = 35.82 --+ 11.84 SE) during July and August 1992. One male was deleted from the final sample due to identification error (final n -- 45). Ages of males younger than 20 years were determined by demographic data of exact year of birth whereas ages of males between 20 and 35 were determined by correlating life histories with known events. Older males (>35 years) were aged by more complicated methods of cross-referencing (Hill and Hurtado 1995). Males w h o reportedly suffered from chronic illnesses such as tuberculosis were excluded from the study as well as those w h o were acutely ill (e.g., colds, pneumonia). Men were recruited randomly in exchange for a communal gift. Subjects were given two 12 x 75 mm polystyrene tubes daily and instructed to collect saliva twice each day, once immediately after waking and once at sunset. Instructions were given verbally in Ach6 and reinforced daily to maximize collection consistency. Variation d u e to individuals having different wake times was minimal since all Ach6
Testosterone Levels among Ach~ Males
167
usually awoke at sunrise and returned from their fields or from the forest at sunset with regularity. Sugarless gum was used as a salivary stimulant. Upon collection, filled tubes were treated with sodium azide (NAN3) to prevent bacterial or fungal contamination. The number of collection days per individual ranged from 1 to 10 (Ix = 5.3). Samples were stored at ambient temperature (ca. 20~ until they were transported to Harvard University where they were immediately placed in frozen storage (-4~ These procedures have previously been validated by Lipson and Ellison (1989).
Assay Procedures Assay procedures follow those of Ellison and colleagues (1988). Salivary samples were thawed and centrifuged for 10 minutes at 3,000 r.p.m, to precipitate proteins and/or mucopolysaccharides. Salivary aliquots of 1.0 ml were pipetted into 18 • 175 mm glass tubes with 100 ~l of tritiated testosterone recovery counts (1,000 cpm/100 ixl) added to quantify extraction efficiency. Aliquots were then extracted by adding 5.0 ml anhydrous ethyl ether and vortexing for 2 minutes. Salivary samples and ether were allowed to separate and then placed in frozen CO 2. Upon freezing of the aqueous saliva, supernatant ether was poured into individual 16 x 100 glass tubes which were then placed under a gentle stream of N 2 and dried in a block heater. The extraction procedure was repeated with the resulting dried residues reconstituted using 1.0 ml of phosphate-gel buffer. Duplicate 400 ;xl aliquots of reconstituted sample were subsequently assayed using a specific antiserum (GDN #250 obtained from G. Niswender, Colorado State University) and a fourposition tritiated testosterone competitor (Amersham Corp., Arlington Heights, IL). Following an overnight incubation at 4~ antibody b o u n d and unbound steroids were separated using dextran-coated charcoal. Scintillation fluid was then added to the b o u n d steroid fraction and measured for beta emissions.
Statistical Analyses Standard descriptive statistics such as means, standard deviations (SD), and standard errors (SE) were calculated for both morning and evening Ach6 salivary testosterone levels. Diurnal patterns of Ach6 salivary testosterone were analyzed using paired t-tests after log transformation of raw values to normalize distributions. Log-transformed interpopulational testosterone levels (Northern Ach6 vs. Efe, Lese, Nepalese) were also analyzed using unpaired, two-tailed t-tests. Previous researchers have cautioned against interpreting interpopulational salivary steroid differences due to possible inter-laboratory variance (Read
168
Human Nature, Vol. 7, No. 2, 1996
1993); however, all of the salivary testosterone values for each of these populations were determined in the same laboratory using identical protocols. Correlations between morning and evening salivary testosterone levels and age, height, weight, and BMI among Ach6 males were calculated using Pearson's product-moment coefficient of correlation on log-transformed data to normalize the distributions and d a m p e n outliers. Results were considered significant at the 0.05 level.
RESULTS Assay Variability Inter-assay variability for Ach6 samples was measured using three separate quality control pools yielding the following results: high pool (~ = 5.34%); medium pool (~ = 5.62%); low pool (.. = 6.27%). Intraassay variability assessed at the 50% binding point (ED 50) of the standard curve was 5.57%.
Salivary Testosterone Levels Ach6 morning salivary testosterone levels are shown in Table 1. Average morning salivary testosterone among Ach6 males was 192 + 12.2 SE pmol/L, with evening salivary testosterone exhibiting a mean of 156 +11.4 SE pmol/L. Diurnal effects among Ach6 males were clearly evident, with 88.8% of subjects demonstrating significantly higher mean morning salivary testosterone in comparison to evening values. As a group, morning salivary testosterone samples were significantly higher than evening samples (paired t = -11.088, d.f. = 89, p < 0.0001), indicative of circadian rhythms observed in other populations (Table 1). No statistically significant relationships were observed b e t w e e n either morning or evening salivary testosterone levels and any of the predefined anthropometric measures--height, weight, or body mass index (BMI). However, with the exclusion of one outlier, a mild positive correlation was Average Morning and Evening Salivary Testosterone values (pmol/L) among Ach6 Males
Table 1.
Morning
Evening
N
Mean
SD
SE
Mean
SD
SE
45
192
81.5
12.2
156
76.7
11.4
3"I
] .9
y=0.016X+ 1.797 r=0.133
2.5.1 o ~
)o
1
.9
$
1.5-
o
:
o
0
o o 1
I
I
I
I
I
20
22.5
25
27.5
30
32.5
0
Log of AM Salivary Testosterone (pmol/L)
BMI
Figure I
Scattergram of average m o r n i n g salivary testosterone; regression with body mass index (BMI) for Ach~ males. 800
-
600 -
[]
AMT~•
[]
PMTsal+ 1.0SE
T %*,.,
o
400 -
T v',.
T
T ,_-i-_,|
%. :.T.T.:m
~
200 -
~,. ~
-- i~]
T
:,:.:,:!
~-~, :';';';i x x :;:::,'! x .. "'":'! k k ~.-C.-'.m \ \ :':+!
0 Boston
Lese
Efe
Nepal
Ache
Population
Figure 2.
Bar graph of average m o r n i n g a n d e v e n i n g salivary testosterone levels a m o n g Ach6, Efe, Lese, a n d Nepal males. 169
H u m a n Nature, Vol. 7, No. 2, 1996
170 t~
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