Abstract
In older people, less diurnal variability in cortisol levels has been consistently related to worse physical performance, especially to slower walking speed (WS). The cortisol awakening response (CAR) is a discrete component of the hypothalamic-pituitary-adrenal axis that has been related to several health problems, such as cardiovascular disease and/or worse performance on executive function and memory. The relationship between the CAR and physical performance in older people is poorly understood. In this study, in 86 older people (mean age = 64.42, SD = 3.93), we investigated the relationship between the CAR and WS, a commonly used measure of physical performance in the older population that has also been related to health problems, such as cardiovascular disease and executive function performance in older people. Additionally, we studied whether the relationship between the CAR and WS was independent from cortisol levels on awakening and several possible confounders. Results showed that a CAR of reduced magnitude (measured with 3 samples each day, for two consecutive days, and calculated as the area under the curve with respect to the increase), but not cortisol levels on awakening, was related to slower WS. In addition, this relationship was independent from cortisol levels on awakening. It is possible that a CAR of reduced magnitude would contribute to less diurnal cortisol variability, affecting physical performance. Additionally, it is possible that a CAR of reduced magnitude affects WS through a possible negative effect on executive function, or that the association between the CAR and WS is due to the fact that both are related to similar health problems and to changes in cognitive performance in older people.
Highlights
The activity of the hypothalamic-pituitary-adrenal axis (HPA-axis) and the change in cortisol levels follow a circadian rhythm
Our findings confirm the results observed by Gardner et al [8] and Gardner et al [9], but they contrast with those observed in Kumari et al [7] and Johar et al [10], who observed the opposite relationship and no relationship, respectively
It is worth noting that, compared to this previous research, in the present study we used three salivary samples on two consecutive weekdays to measure cortisol levels, we controlled for possible non-adherence to the protocol, enhancing the reliability of cortisol awakening response (CAR) measurements, and we controlled for perceived stress in the previous month and self-reported physical activity
Summary
The activity of the hypothalamic-pituitary-adrenal axis (HPA-axis) and the change in cortisol levels follow a circadian rhythm. This circadian rhythm involves three discrete components: (i) the cortisol awakening response (CAR), (ii) a decline in cortisol levels during the rest of the day (showing a sharp decline in the morning and a gradual decline in the afternoon and early evening); and (iii) an increase in cortisol levels from the second half of the night until waking [1]. The CAR consists of a rapid 50 to 160% increase in cortisol concentration after awakening that. CAR and Walking Speed in Older People
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