Global variation in diurnal cortisol rhythms: evidence from Garisakang forager-horticulturalists of lowland Papua New Guinea

Figures & data

Figure 1. Garisakang unadjusted mean (shaded interquartile range) waking cortisol concentration (top) and diurnal cortisol slope (bottom) across the lifespan, stratified by sex.

Table 1. Sample characteristics (mean, SD) for subadults and adults by sex.

	Subadults (age 4.3–15.9 years)		Adults (age 16.0–70.1 years)
	Females (N = 32)	Males (N = 51)	Females (N = 39)	Males (N = 47)
Age (years)	10.9 (3.6)	10.3 (3.3)	34.6 (14.6)	29.9 (14.4)
Height (cm)	131.8 (16.8)	127.4 (17.3)	152.7 (3.9)	161.6 (5.6)
Height-for-age^a	−2.0 (1.0)	−2.1 (0.8)	–	–
Weight (kg)	28.0 (10.3)	26.0 (9.1)	45.2 (6.2)	54.5 (6.6)
Weight-for-age^a	–0.6 (1.5)	−0.8 (1.4)	–	–
BMI (kg/m^2)	16.2 (1.9)	15.7 (1.5)	19.4 (2.7)	20.9 (1.9)
BMI-for-age^a	−0.9 (0.7)	−0.9 (0.8)	–	–
Saliva samples (#/participant)	8.9 (4.1)	9.9 (4.0)	10.6 (3.9)	9.6 (4.6)
Waking saliva collection time (hh:mm)	6:37 (0:30)	6:42 (0:30)	6:35 (0:29)	6:42 (0:37)
Evening saliva collection time (hh:mm)	17:48 (1:50)	17:59 (1:17)	17:55 (1:26)	17:58 (1:35)
Waking cortisol (nmol/L)	5.16 (1.42)	4.80 (1.39)	4.97 (1.47)	4.72 (1.42)
Cortisol diurnal slope (nmol/L/h)^b	−0.19 (0.14)	−0.20 (0.12)	−0.15 (0.17)	−0.16 (0.11)

^aSubadult age and sex-specific z-scores calculated using World Health Organization multinational growth references (De Onis, 2007). ^bCortisol diurnal slope calculated as slope = (evening cortisol concentration − waking cortisol concentration)/hours between waking and evening sample collection.

Figure 2. Garisakang all-age estimated mean cortisol concentration (shaded 95% CI) by time post-waking, stratified by sex.

Table 2. Multilevel models of Garisakang log₁₀-transformed diurnal cortisol rhythms (nmol/L).

	Model 1		Model 2
Fixed effect	Estimate (SE)	p Value	Estimate (SE)	p Value	Interpretation^a
Intercept	0.687 (0.007)	<.001	0.705 (0.015)	<.001	Mean waking cortisol of 4.86 nmol/L
Age (years)	–	–	−0.000 (0.000)	.970	N.S.
Sex (male = 1)	–	–	−0.030 (0.014)	.039	−0.32 nmol/L if male
Time post-waking	−0.028 (0.001)	<.001	−0.031 (0.002)	<.001	Mean cortisol decline of 6.20%/h
Age (years)	–	–	0.001 (0.000)	.042	+0.03%/h per year older
Sex (male = 1)	–	–	0.001 (0.002)	.645	N.S.
Random effect	Variance (SD)	p Value	Variance (SD)	p Value
Level 1 intercept	0.023 (0.151)	<.001	0.023 (0.151)	<.001	–
Level 2 intercept	0.004 (0.064)	<.001	0.004 (0.063)	<.001	–
Time post-waking	0.001 (0.010)	–	0.001 (0.010)	–	–

^a Estimates for log cortisol concentrations were transformed to standard values to enhance interpretation.

Table 3. Comparative studies reporting salivary diurnal cortisol rhythms in diverse populations. The findings of the present study are provided in bold.

Population	Age (years)	N	Samples/participant	Waking cortisol(nmol/L)	Cortisol slope(nmol/L/h)	References
Garisakang	4–15	83	9.5	4.9	−0.19	Urlacher et al. (this study)
Garisakang	16–70	86	10.0	4.8	−0.16	Urlacher et al. (this study)
Tsimane’	2–15	175	5.1	5.3	−0.21	Nyberg (2012)
Tsimane’	16–82	128	5.3	6.4	−0.26	Nyberg (2012)
Filipino	20–22	1490	2.0	7.5	−0.33	Desantis et al. (2015)
Caribbean	0–18	264	87.6	15.9	–	Flinn and England (1997)
USA (Atlanta)	5–6	28	10–14	10.4	−0.51	Decaro and Worthman (2008)
US CARDIA	18–30	781	1.9	20.3	−0.78	Cohen et al. (2006)
US MIDUS	33–84	1694	8.0	15.2	−0.73	Stawski et al. (2013)

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