Abstract
Physical fitness has salutary psychological and physical effects in older adults by promoting neuroplasticity and adaptation to stress. In aging, however, the effects of fitness on the hypothalamic-pituitary-adrenal (HPA) axis are mixed. We investigated the association between cardiorespiratory fitness and HPA activity in healthy elderly men (n = 22, mean age 68 y; smokers, obese subjects, those taking drugs or reporting recent stressful events were excluded), by measuring in saliva: i) daily pattern of cortisol secretion (6 samples: 30’ post-awakening, and at 12.00, 15.00, 18.00, 21.00, 24.00 h); and ii) the cortisol response to a mental challenge. Cardiorespiratory fitness (VO2max) was estimated using the Rockport Walking Test and the participants were assigned to high-fit (HF, ≥60°, n = 10) and low-fit (LF, ≤35°, n = 12) groups according to age-specific percentiles of VO2max distribution in the general population. At all daytimes, basal cortisol levels were lower in the HF than the LF group, most notably in the evening and midnight samples, with a significant main effect of physical fitness for cortisol levels overall; the area-under-the-curve for total daily cortisol output was significantly smaller in the HF group. Among the subjects who responded to mental stress (baseline-to-peak increment >1.5 nmol/L; n = 13, 5 LF, 8 HF), the amplitude of cortisol response and the steepness of recovery decline displayed an increasing trend in the HF subjects, although between-group differences failed to reach the threshold for significance. In conclusion, cardiorespiratory fitness in healthy aging men is negatively correlated with daily cortisol output and contributes to buffering the HPA dysregulation that occurs with advancing age, thus possibly playing a beneficial role in contrasting age-related cognitive and physical decline.
Highlights
Aging is a complex, multifactorial process which shows great individual variability
Stressrelated psychosocial and affective dimensions seem to play a role in moderating age-related changes in HPA activity: in a large sample spanning 50 years of adulthood, the increase in cortisol output across the day was shown to correlate with higher levels of average negative affect [9]; in older adults, notably those reporting high levels of perceived stress, decline in selfesteem has been shown to predict an elevated diurnal cortisol output [10]; a 4-year longitudinal study involving 157 community-dwelling aged persons showed that levels and increases of sleep duration buffered the long-term elevation of diurnal cortisol secretion [11]
Age-related effects on cortisol secretion have mainly been ascribed to the impairment of feedback inhibition of HPA activity due to neuronal loss within specific brain areas, such as prefrontal cortex and hippocampus, which exert an inhibitory action on stress-sensitive neurons in the amygdala and hypothalamus [12,13,14]
Summary
Multifactorial process which shows great individual variability. The trajectory of aging could be related to a variety of factors, including individual differences in the hypothalamic-pituitary-adrenal (HPA) axis activity [1, 2]. Cortisol secretion levels follows a typical circadian rhythm, sharply increasing within 1 hour after waking and steadily declining thereafter, reaching a nadir in the late evening hours [3] Major changes in this diurnal pattern have consistently been observed with aging. Stressrelated psychosocial and affective dimensions seem to play a role in moderating age-related changes in HPA activity: in a large sample spanning 50 years of adulthood, the increase in cortisol output across the day was shown to correlate with higher levels of average negative affect [9]; in older adults, notably those reporting high levels of perceived stress, decline in selfesteem has been shown to predict an elevated diurnal cortisol output [10]; a 4-year longitudinal study involving 157 community-dwelling aged persons showed that levels and increases of sleep duration buffered the long-term elevation of diurnal cortisol secretion [11]. Frequent HPA activation and increased cortisol secretion are proposed as being etiological in the development of several chronic conditions that become manifest in the older population, including cardiovascular disease [16], cognitive decline [17,18,19], depression [20, 21], and frailty [22, 23]
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