Abstract
BackgroundCortisol is often used as a biological marker for stress. When measured in urine or serum, representing a short-term measurement of the hormone, it has been associated with unfavorable sleep characteristics and both low and high physical activity levels. However, cortisol in hair represents a long-term stress measure and has been suggested as a promising new marker for chronic stress. Therefore, we aimed to examine the association between objectively measured sleep, physical activity and hair cortisol levels in preschool children.MethodsIn order to obtain objective measures of physical activity and sleep habits, 54 children aged 2–6 years wore an ActiGraph for 5 consecutive days and nights. For chronic stress measurements of each child, hair was cut from the back of the head close to the scalp for analysis of cortisol levels. Associations between measured sleep quality and quantity and level of physical activity and hair cortisol levels were estimated using linear regression analysis, presented as β. Results were adjusted for sex, age and BMI z-score.ResultsWe found no significant association between log-transformed cortisol (pg/mg) and sleep duration (hours) (β = − 0.0016, p = 0.99), sleep efficiency (β = − 3.1, p = 0.18), sleep latency (β = 0.015, p = 0.16) or physical activity level (100 counts per min) (β = 0.014, p = 0.22). However, sleep latency (min) was directly associated with physical activity (counts per min) levels (β = 35.2, p = 0.02), while sleep duration (hours) (β = − 142.1, p = 0.55) and sleep efficiency (%) (β = − 4087, p = 0.26) showed no significant associations.ConclusionsIn our study, a high physical activity level was associated with poorer sleep habits. Neither sleep quality nor physical activity were related to long term cortisol exposure. These results are among the first to study associations between objectively measured sleep, physical activity and chronic cortisol levels among preschool children. More and larger studies are therefore needed.
Highlights
Cortisol is often used as a biological marker for stress
Previous studies that have examined the association between sleep quality and salivary cortisol levels among children seem to generally agree that shorter sleep duration and/or longer sleep onset latency, were directly related to cortisol measured in saliva, in both longitudinal and cross-sectional studies
Two studies that examined the association of salivary cortisol on sleep characteristics among children both reported a higher morning cortisol among children that presented with poor sleep habits compared to those with better sleep habits [6, 15]
Summary
Cortisol is often used as a biological marker for stress. When measured in urine or serum, representing a short-term measurement of the hormone, it has been associated with unfavorable sleep characteristics and both low and high physical activity levels. We aimed to examine the association between objectively measured sleep, physical activity and hair cortisol levels in preschool children. There are multiple ways of measuring cortisol, which include saliva, urine, blood and, more recently, hair The latter measures long term cortisol levels (chronic stress) [11] while the three former are short term measurements (acute stress) [12]. Cortisol measured in hair is a relatively new measurement, and to our knowledge, no previous studies have examined its relationship with sleep quality or PA in children. Previous studies that have examined the association between sleep quality and salivary cortisol levels among children seem to generally agree that shorter sleep duration and/or longer sleep onset latency, were directly related to cortisol measured in saliva, in both longitudinal and cross-sectional studies. Associations between sleep and cortisol, measured in saliva, serum or urine, are often modest or lacking [11, 17,18,19]
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