Distribution characteristics of salivary cortisol measurements in a healthy young male population.
BACKGROUND
Salivary cortisol has been used in various fields of science as a non-invasive biomarker of stress levels. This study offers the normative reference values of cortisol measurement for healthy young males.


RESULTS
Salivary cortisol levels were measured in 267 healthy young males (age: 21.7 ± 1.5 years) in the early morning on two consecutive days and were analyzed by radioimmunoassay. Frequency distribution analysis was conducted with mean values of the measurements taken on the 2 days. The mean salivary cortisol level was 20.39 ± 7.74 nmol/l (median: 19.31 nmol/l). The skewness and kurtosis of the distribution of the raw data were 0.72 and 0.68, respectively. They were both improved by a square root transformation but not by a logarithmic transformation.


CONCLUSIONS
The skewness of the distribution for salivary cortisol measured in the early morning is considerably smaller than that previously reported from afternoon measurements. A "floor effect" may be an explanation for the difference in the distribution characteristics of salivary cortisol.
Center for Environment, Health and Field Sciences, Chiba University, Chiba, Japan. kobayasi@ishikawa-nu.ac.jp.
Hiromitsu
H
Kobayashi
Center for Environment, Health and Field Sciences, Chiba University, Chiba, Japan. ymiyazaki@faculty.chiba-u.jp.
Yoshifumi
Y
Miyazaki
D000328:Adult; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis*; D007564:Japan / Q000453:epidemiology; D008297:Male; D012016:Reference Values; D012463:Saliva / Q000737:chemistry*; D055815:Young Adult
D006854:Hydrocortisone