The impact of aerobic fitness on arterial stiffness and adrenal cortex hormones in middle-aged and older adults

Abstract

An increase in arterial stiffness with advance aging is a risk for cardiovascular disease. Cardiovascular dysfunction is associated with the imbalance of adrenal cortex hormones, especially with the cortisol/dehydroepiandrosterone sulfate (DHEAs) ratio. However, the impact of aerobic fitness on arterial stiffness and cortisol/DHEAs ratio is unclear. The aim of this study was to investigate the relationship between aerobic fitness, arterial stiffness, and cortisol/DHEAs ratio. A total of 198 middle-aged and older adults (aged 50–79 years old) participated in this study. The aerobic fitness evaluated by peak oxygen consumption (VO_2peak), carotid-femoral pulse wave velocity (cfPWV) as an indicator of arterial stiffness, and serum cortisol and DHEAs and their ratio were measured. The subjects were divided into the lower (n = 100) and the higher (n = 98) aerobic fitness groups based on the median value of VO_2peak. There were no significant differences in serum cortisol and DHEAs concentration alone between the lower and higher fitness groups. However, the cortisol/DEHAs ratio and cfPWV in the higher fitness group was smaller than in the lower fitness group (p < 0.05). The cortisol/DHEAs ratio was significantly correlated with cfPWV (r = 0.159, p < 0.05). These findings suggest that the cortisol/DHEAs ratio is associated with aerobic fitness and arterial stiffness in middle-aged and older adults.

IT IS WELL ESTABLISHED that arterial stiffness increases with advancing age [1]. Stiffened artery lead to elevate systolic blood pressure and left ventricular after load, and decreased coronary perfusion [2, 3]. An increase in arterial stiffness is an independent risk factor for cardiovascular diseases [4]. Therefore, attenuating the increase in arterial stiffness is preferable in middle-aged and older adults. Previous studies imply that regular exercise and higher fitness reduce arterial stiffness [5], and exercise capacity is associated with arterial stiffness [6]. However, little is known about the underlying mediated the relationship between exercise and arterial stiffness.

Aging also affects the secretion of adrenal steroid hormones, a key component of stress response in the hypothalamic-pituitary-adrenal (HPA) axis [7]. Two hormones, cortisol and dehydroepiandrosterone (DHEA), are secretory signaling steroids released from the adrenal cortex of the zona fasciculata and the zona reticularis, respectively, and they have opposing actions that DEHA appears to act as a counterbalance to the negative implication of cortisol for health outcome [8]. It is well known that older adults have higher circulating cortisol and lower DHEA sulfate (DHEAs) levels, and the decline in DHEAs with age is termed as adrenopause [9, 10]. Elevated cortisol and reduced DHEAs are associated with blood pressure and cardiovascular function [11, 12], and DHEA replacement can improve arterial stiffness in elderly men and women [13]. Moreover, the imbalance of high cortisol and low DHEAs levels and consequent increase in the cortisol/DHEAs ratio is thought to be a significant marker of health deterioration with age [14]. Additionally, the ratio of cortisol and DHEAs is associated with mental disorders, and cardiovascular diseases, as well as all-cause and cause-specific mortality [15, 16]. Recently, Heaney et al. [17] have reported that the cortisol/DHEAs ratio is lower in physically active individuals with high life-event stress. Taken together, it is plausible that adrenal hormones, especially the cortisol/DHEAs ratio, may be associated in higher fitness-related lower arterial stiffness. However, there has been no study investigating the association among aerobic fitness, adrenal cortex hormones, and arterial stiffness in a large number of samples.

The purpose of this study was to investigate the impact of aerobic fitness on adrenal hormones and arterial stiffness. Therefore, the present cross-sectional study examined associations between adrenal hormones including cortisol, DHEAs, and their ratio, the aerobic exercise capacity, and the arterial stiffness in a cohort of middle-aged and older adults. We hypothesize that aerobic fitness-related difference in arterial stiffness is associated with the level and ratio of cortisol and DHEAs.

Materials and Methods

Subjects

This study used a cross-sectional design and a total of 198 middle-aged and older healthy adults (81 men and 117 women, age 50–79 years) participated in this study. Subjects with a smoking habit, anti-hypertensive medication, hormone replacement therapy, cardiovascular, or cerebrovascular disease were excluded. All women were postmenopausal. All potential risks associated with the study were explained to the subjects, and written informed consent was provided by all participants. All procedures were reviewed and approved by the ethical committee of the University of Tsukuba, Japan.

Procedures

All experiments were conducted in the morning after a 12-hour overnight fast. Subjects abstained from alcohol and caffeine for at least 12 hours and did not exercise for at least 24 hours before the experiments. Measurements were performed in a quiet, temperature-controlled room (24–26°C). We measured arterial stiffness, hemodynamics, adrenal hormones, blood sample chemistry, and aerobic exercise fitness.

Measurements

Carotid-femoral pulse wave velocity (cfPWV), indicative of arterial stiffness, was measured by a semi-automated vascular testing system in participant at a supine position. Briefly, left carotid and left femoral pressure waveforms were obtained by two applanation tonometry sensors incorporating an array of 15 transducers (Form PWV/ABI, Colin Medical Technology, Komaki, Japan). The distance between the left common carotid and left common femoral arterial recording sites was divided by the transit time to calculate cfPWV. Brachial systolic blood pressure and diastolic blood pressure, and heart rate were measured with an electrocardiogram and oscillometric extremity cuff. Blood samples were collected from the antecubital vein after overnight fasting. cfPVW and blood pressure measurements were taken at least three times that were recorded over a 30 s period.

Plasma and serum were collected and stored at –80°C, until they were used for specific assays. Serum cortisol, serum DHEAs concentration, plasma noradrenaline concentration, and plasma aldosterone concentration were determined using chemiluminescence immunoassay, chemiluminescence enzyme immunoassay, high- performance liquid chromatography, and radioimmunoassay, respectively. The intra-assay coefficient of variation was 2.23% for noradrenaline, 6.7% for aldosterone, 1.74% for DHEAs, and 2.51% for cortisol measurements. Serum total cholesterol, high density lipoprotein cholesterol, low density lipoprotein cholesterol, triglyceride, and plasma glucose were determined using the standard enzymatic technique, all by a commercial laboratory (LSI Medience Corporation Ltd., Tokyo, Japan).

Peak oxygen uptake (VO_2peak) was measured during the incremental exercise test on a bicycle ergometer (AEROBIKE 75XL III; Konami Wellness, Tokyo, Japan) with online computer-assisted circuit spirometer (AE300S; Minato Medical Science, Osaka, Japan). All subjects performed a symptom-limited cycling exercise test, which consisted of warm-up at 20 W for 2 minutes and followed by a 10 W increase per minute. We measured the average of oxygen uptake every 30 s during the exercise test until exhaustion or if one of following criteria was met: clinical complaints of exhaustion by the participant, unable to maintain cadence (<50 rpm) for several seconds, or attainment of age-predicted maximal heart rate (208 – 0.7 × age) [18]. Heart rate was monitored continuously with an electrocardiogram. VO_2peak was defined as the highest value recorded during the test and used as an index of aerobic fitness.

Statistical analyses

All data are expressed as means ± standard deviation (SD). To assesses the effect of aerobic exercise fitness, the subjects were divided into the lower or a higher fitness groups based on the median value of a VO_2peak in each age group (over or under 65 years old) and sex (men or women). The analysis of normality was performed with the Shapiro-Wilk test. The independent t-test or Mann-Whitney U test was used to evaluate group differences in continuous variables based on the result of the Shapiro-Wilk normality test. Pearson’s product correlation analysis was used to test the associations between cfPWV and adrenal hormone level after skewed variables were log-transformed and achieved normal distributions. All statistical data analyses were performed using SPSS software (Version24; IBM, Armonk, NY), and statistical significance was set a piriori at p < 0.05 for all comparisons.

Results

Table 1 shows the characteristics of the study participants. There were no significant differences in age, height, cholesterols, triglyceride, glucose, heart rate, or blood pressures between the lower and higher fitness groups. Weight and cfPWV in the higher fitness group was significantly smaller than that in the lower fitness group. VO_2peak in the higher fitness group was significantly higher than that in the lower fitness group. Table 2 shows the impact of aerobic fitness on adrenal hormones. Significant group differences were not found in noradrenaline, aldosterone, cortisol, and DHEAs concentration levels. However, the cortisol/DHEAs ratio in the higher fitness group was significantly smaller than that in the lower fitness group (0.088 ± 0.059 vs. 0.103 ± 0.058, p < 0.05) (Fig. 1). Furthermore, there was a significant positive correlation between the cortisol/DHEAs ratio and cfPWV (r = 0.159, p < 0.05) (Fig. 2).

Table 1 Characteristics and arterial stiffness in lower and higher aerobic fitness groups

	All	Lower fitness	Higher fitness
n (men/women)	198 (81/117)	100 (40/60)	98 (41/57)
Age, years	63 ± 7	63 ± 7	63 ± 6
Height, cm	161 ± 8	161 ± 8	161 ± 8
Weight, kg	59 ± 9	60 ± 9	57 ± 9*
Total cholesterol, mg/dL	222 ± 34	222 ± 35	223 ± 33
HDL cholesterol, mg/dL	64 ± 16	63 ± 16	66 ± 15
LDL cholesterol, mg/dL	135 ± 31	135 ± 33	134 ± 28
Triglyceride, mg/dL	98 ± 50	98 ± 51	98 ± 50
Glucose, mg/dL	96 ± 16	98 ± 19	94 ± 11
Heart rate, bpm	60 ± 7	61 ± 8	59 ± 7
Systolic blood pressure, mmHg	126 ± 15	127 ± 16	124 ± 14
Diastolic blood pressure, mmHg	77 ± 10	77 ± 10	76 ± 9
cfPWV, cm/s	958 ± 178	985 ± 209	931 ± 136*
VO2peak, mL/min/kg	23 ± 5	20 ± 3	26 ± 4*

Data are shown in Means ± SD. HDL, high density lipoprotein; LDL, low density lipoprotein; VO_2peak, peak oxygen uptake; cfPWV, carotid-femoral pulse wave velocity. * p < 0.05 vs. Lower fitness group.

Table 2 Adrenal hormones in lower and higher aerobic fitness groups

	All	Lower fitness	Higher fitness
Noradrenaline, ng/mL	0.37 ± 0.18	0.36 ± 0.17	0.37 ± 0.19
Aldosterone, pg/mL	132 ± 50	133 ± 50	131 ± 50
DHEAs, μg/dL	124 ± 74	118 ± 73	130 ± 74
Cortisol, μg/dL	9 ± 4	10 ± 4	9 ± 4

Data are shown in Means ± SD. DHEAs, dehydroepiandrosterone sulfate.

Fig. 1

Cortisol/DHEAs (dehydroepiandrosterone sulfate) ratio in lower and higher aerobic fitness group.

Fig. 2

The relationship between cortisol/DHEAs (dehydroepiandrosterone sulfate) ratio and cfPWV (carotid-femoral pulse wave velocity).

Discussion

This study evaluated aerobic fitness, arterial stiffness, and adrenal hormones in middle-aged and older adults. The salient findings of the present study were that the higher aerobic fitness group had lower arterial stiffness and cortisol/DHEAs ratio was correlated with arterial stiffness. Physiological response to various stresses induces the activation of the endocrine system, such as the HPA axis, resulting in the secretion of cortisol and DHEA secreted from the adrenal cortex. It is well known that chronic high cortisol concentration reduces immune function and cognitive function [10]. In contrast, DHEA has an anti-glucocorticoid effect that regulates cortisol and then attenuates the increase in cortisol concentration [19]. Previous studies have demonstrated that the ratio of increased cortisol to decreased DHEAs with aging was associated with depression [20, 21]. Furthermore, a higher cortisol/DEHAs ratio was observed in patients with cardiovascular diseases [16]. In the present study, we found that the cortisol/DHEAs ratio was correlated with both VO_2peak and cfPWV in general healthy middle-aged and older populations. These results suggest that age-related deterioration in adrenal cortical hormone balance is associated with aerobic exercise capacity and arterial function.

Aerobic exercise fitness evaluated by VO_2peak is related to arterial function including its stiffness; thus, people who have undergo endurance training have more compliant artery than sedentary [22]. It has been reported that exercise training-related decrease in arterial stiffness is mediated by several physiologically active substances such as endothelin-1 and asymmetric dimethylarginie or steroid hormone such as testosterone [23-25]. These steroid hormones are founded to enhance endothelial function [26]. In this study, the ratio of cortisol to DHEAs was significantly different between aerobic fitness categories and was correlated with arterial stiffness rather than cortisol or DHEAs alone. These results suggested that fitness-related changes in arterial stiffness would be partly mediated by adrenal cortex hormones.

Physical and/or psychological stress increase the levels of both DHEA and cortisol. DHEA has an anti-glucocorticoid effect that suppresses the elevation of cortisol levels [27]. Over secretion of cortisol, as compared to that of DHEAs, seems to modulate adrenocortical and HPA activity and catabolic/anabolic balance [28]. Furthermore, the balance of two adrenal cortex hormones is higher in Alzheimer’s disease and ischemic stroke [29, 30]. In the present study, higher fitness level was associated with a lower cortisol/DHEAs ratio and cfPWV, and there was a weak but significant correlation between these two entities. The secretions of cortisol and DHEAs is complexly co-regulated by each other, and the balance between the two hormones has been usually considered to be an indicator of the health status [10]. In this regard, the interpretation of hormone ratio should be made cautiously, since the physiological mechanism underlying the effects of the hormone ratio is poorly understood [31]. It is possible that the analyses of such a hormone ratio can become a good marker of arterial stiffness and cardiovascular risks. However, further studies are warranted to understand the specific hormone ratio that can be indicative of a balance between adrenal hormones, and the underlying mechanisms that contribute to exercise fitness and vascular function.

There is a small but significant difference in the cortisol/DHEAs ratio between the higher and lower fitness groups (Fig. 1). Whether such a small difference is physiologically significant remains to be determined. However, it should be noted that a cohort-based study demonstrated that the cortisol/DHEAs level in hypertensive patient was significantly higher than normotensive peers, although such a difference was not so large (0.099 ± 0.082 vs. 0.086 ± 0.051, 13%) [32]. Moreover, another study reported that acute aerobic exercise decreased about 10% of cortisol/DHEAs level in healthy older adults [33]. Collectively, these findings suggest that >10% deference in the cortisol/DHEAs levels may be associated with exercise-induced vascular adaptation.

The decrease in DHEAs with age is known to deteriorate cardiovascular health [11]. DHEA has a favorable effect on vascular function including nitric oxide synthase activation, endothelial cell proliferation, and endothelial-dependent dilation [34]. In this regard, a previous study on young adults reported that there is no difference in DHEAs concentrations between endurance-trained men with higher aerobic capacity and sedentary peers [35]. Similarly, in this study, no significant difference was evident in each concentration of DHEAs as well as noradrenaline, aldosterone, and cortisol alone between the higher and lower aerobic fitness groups in middle-aged and older adults. Thus, it is unlikely that aerobic exercise capacity is associated with the individual concentration of adrenal hormones. Taking together, the cortisol/DHEAs ratio may reflect exercise-related changes in arterial stiffness, which implicates the importance of assessing their balance. A potential benefit of assessing the cortisol and DHEAs as a ratio is that it captures the preferential production of one hormone over the other.

The findings of the current study have clinical implications. Increase in arterial stiffness with age is a strong risk factor for total cardiovascular events in general healthy populations [36]. In this regard, aerobic exercise fitness is known to have a favorable effect on the arterial aging [37]. Gando et al. [38] reported that higher aerobic fitness exhibited lower arterial stiffness progression after 2 years follow up. In accordance with the results of previous studies, our findings demonstrated that arterial stiffness was associated with aerobic fitness, and adrenal hormone levels, the cortisol/DHEAs ratio. These findings highlight the importance of the evaluating and the management of aerobic fitness and adrenal hormone balance in preventing cardiovascular disease.

The present study has some limitations. First, this study focused only on healthy middle-aged and older adults, and we observed a blunted effect of aerobic fitness on health-related outcomes such as the blood pressure and parameters of blood chemistry. The findings of this study did not include other populations, such as young adults or patients with mental disorders, hypertension, and diabetes mellitus. Second, DHEA (and DHEAs) is converted into androgens through androstenedione [39]. It has been also reported that arterial stiffness and endothelial function are associated with the level of testosterone in adult men [26, 40]. However, testosterone levels were not assessed in this study since testosterone is converted to estradiol in women, and testosterone level is very low in women than in men. Third, the study subjects were not analyzed separately each sex. It has been reported that in middle-aged and older populations the cortisol/DHEAs ratio was higher in women than in men [41]. Similarly, women in the present study had a higher cortisol/DHEAs ratio than men, although the impact of aerobic fitness was not different between men and women. These observations suggest that aerobic fitness is similarly associated with adrenal and arterial function in both men and women. Forth, the present study was a cross-sectional study that cannot determine the cause-effect relationship of aerobic exercise, the adrenal hormone ratio and arterial stiffness. Further studies are warranted to investigate the effects of regular exercise on the relation between adrenal hormones and arterial stiffness.

In conclusion, we demonstrated that the higher aerobic fitness group exhibited lower arterial stiffness and cortisol/DEHAs ratio in healthy middle-aged and older adults. Moreover, arterial stiffness correlated with the cortisol/DHEAs ratio. The results of the present study imply that the balance of adrenal cortical hormones is important for aerobic exercise-related decreases in arterial stiffness.

Acknowledgements

This work was supported by the Japan Society for the Promotion of Science KAKENHI, Grand Number 16K16594.

Disclosure

None of the authors have any potential conflicts of interest associated with this research.

References

• 1   Smulyan  H,  Asmar  RG,  Rudnicki  A,  London  GM,  Safar  ME (2001) Comparative effects of aging in men and women on the properties of the arterial tree. J Am Coll Cardiol 37: 1374–1380.
• 2   Tomiyama  H,  Arai  T,  Koji  Y,  Yambe  M,  Motobe  K, et al. (2004) The age-related increase in arterial stiffness is augmented in phases according to the severity of hypertension. Hypertens Res 27: 465–470.
• 3   Boutouyrie  P,  Tropeano  AI,  Asmar  R,  Gautier  I,  Benetos  A, et al. (2002) Aortic stiffness is an independent predictor of primary coronary events in hypertensive patients: a longitudinal study. Hypertension 39: 10–15.
• 4   O’Rourke  MF (1999) Isolated systolic hypertension, pulse pressure, and arterial stiffness as risk factors for cardiovascular disease. Curr Hypertens Rep 1: 204–211.
• 5   Tanaka  H,  Dinenno  FA,  Monahan  KD,  Clevenger  CM,  DeSouza  CA, et al. (2000) Aging, habitual exercise, and dynamic arterial compliance. Circulation 102: 1270–1275.
• 6   Vaitkevicius  PV,  Fleg  JL,  Engel  JH,  O’Connor  FC,  Wright  JG, et al. (1993) Effects of age and aerobic capacity on arterial stiffness in healthy adults. Circulation 88: 1456–1462.
• 7   Phillips  AC,  Carroll  D,  Gale  CR,  Lord  JM,  Arlt  W, et al. (2010) Cortisol, DHEA sulphate, their ratio, and all-cause and cause-specific mortality in the Vietnam Experience Study. Eur J Endocrinol 163: 285–292.
• 8   Saccò  M,  Valenti  G,  Corvi Mora  P,  Wu  FC,  Ray  DW (2002) DHEA, a selective glucocorticoid receptor antagonist: its role in immune system regulation and metabolism. J Endocrinol Invest 25: 81–82.
• 9   Deuschle  M,  Gotthardt  U,  Schweiger  U,  Weber  B,  Körner  A, et al. (1997) With aging in humans the activity of the hypothalamus-pituitary-adrenal system increases and its diurnal amplitude flattens. Life Sci 61: 2239–2246.
• 10   Buford  TW,  Willoughby  DS (2008) Impact of DHEA(S) and cortisol on immune function in aging: a brief review. Appl Physiol Nutr Metab 33: 429–433.
• 11   Hougaku  H,  Fleg  JL,  Najjar  SS,  Lakatta  EG,  Harman  SM, et al. (2006) Relationship between androgenic hormones and arterial stiffness, based on longitudinal hormone measurements. Am J Physiol Endocrinol Metab 290: E234–E242.
• 12   Akishita  M,  Hashimoto  M,  Ohike  Y,  Ogawa  S,  Iijima  K, et al. (2007) Low testosterone level is an independent determinant of endothelial dysfunction in men. Hypertens Res 30: 1029–1034.
• 13   Weiss  EP,  Villareal  DT,  Ehsani  AA,  Fontana  L,  Holloszy  JO (2012) Dehydroepiandrosterone replacement therapy in older adults improves indices of arterial stiffness. Aging Cell 11: 876–884.
• 14   Elenkov  IJ (2004) Glucocorticoids and the Th1/Th2 balance. Ann N Y Acad Sci 1024: 138–146.
• 15   Young  AH,  Gallagher  P,  Porter  RJ (2002) Elevation of the cortisol-dehydroepiandrosterone ratio in drug-free depressed patients. Am J Psychiatry 159: 1237–1239.
• 16   Hechter  O,  Grossman  A,  Chatterton  RT Jr (1997) Relationship of dehydroepiandrosterone and cortisol in disease. Med Hypotheses 49: 85–91.
• 17   Heaney  JL,  Carroll  D,  Phillips  AC (2014) Physical activity, life events stress, cortisol, and DHEA: preliminary findings that physical activity may buffer against the negative effects of stress. J Aging Phys Act 22: 465–473.
• 18   Tanaka  H,  Monahan  KD,  Seals  DR (2001) Age-predicted maximal heart rate revisited. J Am Coll Cardiol 37: 153–156.
• 19   Buoso  E,  Lanni  C,  Molteni  E,  Rousset  F,  Corsini  E, et al. (2011) Opposing effects of cortisol and dehydroepiandrosterone on the expression of the receptor for activated C kinase 1: implications in immunosenescence. Exp Gerontol 46: 877–883.
• 20   Markopoulou  K,  Papadopoulos  A,  Juruena  MF,  Poon  L,  Pariante  CM, et al. (2009) The ratio of cortisol/DHEA in treatment resistant depression. Psychoneuroendocrinology 34: 19–26.
• 21   van Niekerk  JK,  Huppert  FA,  Herbert  J (2001) Salivary cortisol and DHEA: association with measures of cognition and well-being in normal older men, and effects of three months of DHEA supplementation. Psychoneuroendocrinology 26: 591–612.
• 22   Tanaka  H,  DeSouza  CA,  Seals  DR (1998) Absence of age-related increase in central arterial stiffness in physically active women. Arterioscler Thromb Vasc Biol 18: 127–132.
• 23   Otsuki  T,  Maeda  S,  Iemitsu  M,  Saito  Y,  Tanimura  Y, et al. (2007) Vascular endothelium-derived factors and arterial stiffness in strength- and endurance-trained men. Am J Physiol Heart Circ Physiol 292: H786–H791.
• 24   Tanahashi  K,  Akazawa  N,  Miyaki  A,  Choi  Y,  Ra  SG, et al. (2014) Aerobic exercise training decreases plasma asymmetric dimethylarginine concentrations with increase in arterial compliance in postmenopausal women. Am J Hypertens 27: 415–421.
• 25   Kumagai  H,  Zempo-Miyaki  A,  Yoshikawa  T,  Tsujimoto  T,  Tanaka  K, et al. (2015) Lifestyle modification increases serum testosterone level and decrease central blood pressure in overweight and obese men. Endocr J 62: 423–430.
• 26   Green  DJ,  Hopkins  ND,  Jones  H,  Thijssen  DH,  Eijsvogels  TM, et al. (2016) Sex differences in vascular endothelial function and health in humans: impacts of exercise. Exp Physiol 101: 230–242.
• 27   Karishma  KK,  Herbert  J (2002) Dehydroepiandrosterone (DHEA) stimulates neurogenesis in the hippocampus of the rat, promotes survival of newly formed neurons and prevents corticosterone-induced suppression. Eur J Neurosci 16: 445–453.
• 28   Kamin  HS,  Kertes  DA (2017) Cortisol and DHEA in development and psychopathology. Horm Behav 89: 69–85.
• 29   Armanini  D,  Vecchio  F,  Basso  A,  Milone  FF,  Simoncini  M, et al. (2003) Alzheimer’s disease: pathophysiological implications of measurement of plasma cortisol, plasma dehydroepiandrosterone sulfate, and lymphocytic corticosteroid receptors. Endocrine 22: 113–118.
• 30   Blum  CA,  Mueller  C,  Schuetz  P,  Fluri  F,  Trummler  M, et al. (2013) Prognostic value of dehydroepiandrosterone-sulfate and other parameters of adrenal function in acute ischemic stroke. PLoS One 8: e63224.
• 31   Sollberger  S,  Ehlert  U (2016) How to use and interpret hormone ratios. Psychoneuroendocrinology 63: 385–397.
• 32   Carroll  D,  Phillips  AC,  Lord  JM,  Arlt  W,  Batty  GD (2011) Cortisol, dehydroepiandrosterone sulphate, their ratio and hypertension: evidence of associations in male veterans from the Vietnam Experience Study. J Hum Hypertens 25: 418–424.
• 33   Heaney  JL,  Carroll  D,  Phillips  AC (2013) DHEA, DHEA-S and cortisol responses to acute exercise in older adults in relation to exercise training status and sex. Age (Dordr) 35: 395–405.
• 34   Akishita  M,  Hashimoto  M,  Ohike  Y,  Ogawa  S,  Iijima  K, et al. (2010) Low testosterone level as a predictor of cardiovascular events in Japanese men with coronary risk factors. Atherosclerosis 210: 232–226.
• 35   Sato  K,  Iemitsu  M,  Katayama  K,  Ishida  K,  Kanao  Y, et al. (2016) Responses of sex steroid hormones to different intensities of exercise in endurance athletes. Exp Physiol 101: 168–175.
• 36   Willum-Hansen  T,  Staessen  JA,  Torp-Pedersen  C,  Rasmussen  S,  Thijs  L, et al. (2006) Prognostic value of aortic pulse wave velocity as index of arterial stiffness in the general population. Circulation 113: 664–670.
• 37   Seals  DR,  Nagy  EE,  Moreau  KL (2019) Aerobic exercise training and vascular function with ageing in healthy men and women. J Physiol 597: 4901–4914.
• 38   Gando  Y,  Murakami  H,  Kawakami  R,  Yamamoto  K,  Kawano  H, et al. (2016) Cardiorespiratory fitness suppresses age-related arterial stiffening in healthy adults: a 2-year longitudinal observational study. J Clin Hypertens (Greenwich) 18: 292–298.
• 39   Labrie  F (1991) Intracrinology. Mol Cell Endocrinol 78: C113–C118.
• 40   Vlachopoulos  C,  Ioakeimidis  N,  Miner  M,  Aggelis  A,  Pietri  P, et al. (2014) Testosterone deficiency: a determinant of aortic stiffness in men. Atherosclerosis 233: 278–283.
• 41   Laughlin  GA,  Barrett-Connor  E (2000) Sexual dimorphism in the influence of advanced aging on adrenal hormone levels: the Rancho Bernardo Study. J Clin Endocrinol Metab 85: 3561–3568.