The main objective of this study was to verify the relationship between sarcopenia and salivary cortisol levels in older adults LTCF residents. There is wide variability in the sarcopenia prevalence reported in the literature (25). The sarcopenia prevalence found in the sample (17.1%) is in agreement with another Brazilian study which estimated a prevalence of 17% through a systematic review for the country (12). However, these values are closer to the lower limits of other studies published in the international literature for older adults living in LTCFs, such as in the studies by Shen et al.(3) and Rodríguez-Rejón et al. (26), who found a variation of 22 to 85% and 17.7 to 73.3%, respectively. It is important to highlight that the findings on sarcopenia prevalence are intrinsically related to the assessment methods and instruments, the cut-off points used, the inclusion and exclusion criteria of the sample, as well as linked to the population characteristics of each sample.
The age variable regarding demographic information is noteworthy, as the sarcopenic older adults also had the highest mean age. It is known that the aging process is accompanied by a tendency to decrease muscle mass and strength, and that this process can be modulated by genetics and lifestyle (14). There is strong evidence that the incidence of sarcopenia increases with age (1) and several studies also corroborate this factor among institutionalized older adults (4, 27, 28). However, through a systematic review that investigated the prevalence and factors associated with sarcopenia in LTCFs, Shen et al.(3) found that age still maintains an inconsistent association with sarcopenia and that new studies are necessary to assess this relationship.
Mean arm, hip and waist circumferences, as well as BMI itself, were also lower in the sarcopenic older adult group. This difference may be related to the nutritional status of the subjects, as several studies associate poor nutrition with the presence of sarcopenia (27–30). In addition, it is noteworthy that the BMI measurements are also linked to the adopted skeletal muscle mass prediction calculations. In the present investigation, with the exception of age, no relationship was found between sociodemographic variables and specific chronic health conditions with sarcopenia, although some studies indicate that female gender (27) and cognitive dysfunctions (28), for example, may be associated.
The relationship found between sarcopenia and salivary cortisol, the main objective of this study, can be determined by the difference between the cortisol measurements verified throughout the day, in which the sarcopenic older adult group had higher values than the non-sarcopenic older adult group. In addition to the differences between the values of the first, second and third measurements, the mean value, the decline rate and the amplitude values derived from the cortisol measurements were also higher in the sarcopenic older adult group.
Waters et al. (31) found higher salivary cortisol concentrations in a group of sarcopenic older adults when compared to older adults classified in other body compositions (normal, obese and obese-sarcopenic). These results were expressed both by the cortisol peak after breakfast, as well as by the area under the cortisol curve (AUC) performed during the day.
Yanagita et al. (8) analyzed (among other variables) the balance between the cortisol and dehydroepiandrosterone sulfate (DHEA-S) hormones in sarcopenic and non-sarcopenic older adult patients with Type 2 Diabetes Mellitus. They found that there were significantly higher cortisol values and lower DHEA-S values in the sarcopenic group, which raised the cortisol/DHEA-S ratio. The study showed that a cortisol/DHEA-S ratio ≥ 0.2 was the strongest risk factor for sarcopenia in older adult diabetic patients. Furthermore, they observed that the more severe the sarcopenia, the higher the circulating cortisol levels and lower DHEA-S levels, indicating a probable influence of adrenal hormones on the pathophysiology of sarcopenia. Although the present study did not assess the function of DHEA-S, it was possible to carry out a comparison of cortisol levels alone.
Westbury et al. (32) investigated the association of inflammation markers, including cortisol, with the components of muscle mass, strength and function, in addition to the verification of sarcopenia using the algorithm proposed by the EWGSOP through a longitudinal study among community-dwelling older adults. The authors found that a higher cortisol level was considered a predictor of a decrease in the subjects’ appendicular lean mass after 10.8 years of follow-up.
Another study compared patients, men and women, with adrenal incidentaloma (AI) classified into two groups: non-functioning AI and those with subclinical hypercotisolemia. The results showed that the excess, even if slight, of cortisol present in the second group was associated with lower skeletal muscle mass among female patients (33). This study did not collect enough data for the classification needed for sarcopenia.
These findings reinforce the relationship of the hormone cortisol with sarcopenia and/or with the musculoskeletal system, which is intrinsically related to the pathophysiology of sarcopenia. However, unlike the present study, most of the articles mentioned analyzed cortisol through single collections. This increases the methodological problems of diurnal cortisol assessment, as it is a hormone which undergoes several changes in concentrations throughout the day (7). In addition, the studies used different methods to assess sarcopenia, which also makes it difficult to compare the results.
Cortisol-derived measures, such as cortisol decline index and amplitude, represent diurnal variation in cortisol, and lower values indicate lesser resilience of the HPA axis (34). Both were higher in sarcopenic older adults, indicating a greater drop in cortisol per hour. However, despite the greater descending slope of the cortisol curve, the amount of cortisol in sarcopenic older adults remained higher throughout the day than in non-sarcopenic older adults.
An important fact is that all the older adults identified as sarcopenic in this study were classified as having severe sarcopenia. It is possible that most older adult LTCF residents are considered frail or pre-frail (10) and therefore received the most severe classification for sarcopenia.
A higher cortisol concentration in sarcopenic older adult LTCF residents suggests that these individuals may be more exposed to a greater degree of stress when compared to institutionalized older adults who do not have sarcopenia. Cortisol is considered an important marker of physiological stress. It is released by the adrenal glands from the activation of the HPA axis, and is of substantial importance, since its concentrations interfere in various systems of the body. The normal aging process is associated with changes in the endocrine system with consequent hormonal changes, which include the gradual and sustained increase in glucocorticoids (35).
Sarcopenia is characterized by loss of muscle mass and function, is often associated with age, and can be considered a complex geriatric syndrome whose pathophysiology is not very clear. The systems involved include neural and hormonal regulation, in addition to muscle degradation (36). Tournadre et al. (6) describes that the muscle is a contractile organ which enables the human body to move. In addition, it plays other important roles as it is essential for metabolic homeostasis. Muscle can act in glucose uptake, glycogen storage, lipid oxidation, amino acid release, energy production, as well as serving as an amino acid reservoir for immunocompetent cells.
In an attempt to deepen the understanding of the pathophysiological processes involved in the diagnosis and treatment of sarcopenia, some studies have emphasized biochemical analyzes seeking to find biomarkers which may be associated with sarcopenia (37, 38). In this sense, the present study can contribute by reinforcing the understanding of the cortisol relationship in the complex underlying mechanism of sarcopenia.
Some considerations about the study limitations permeate the fact that more cortisol collections, and in more than one day, could improve understanding of the cortisol concentration curve. In addition, the assessment of sarcopenia was based on the EWGSOP2 algorithm, which has European populations as baseline studies, and which therefore is subject to the need to adapt to the Brazilian population. Regarding the evaluation of the item amount of muscle present in the algorithm used for sarcopenia, a prediction equation validated by the impossibility of applying a gold standard measure of evaluation was used. However, it is worth noting that these limitations were mainly due to the difficulty of using more complex equipment and routines in the LTCF, in addition to all the restrictions (physical, sanitary, temporal, etc.) imposed by them. Finally, the inclusion criteria used which limited the participation of older adults with severe cognitive impairments or severe physical disabilities, may have excluded the participation of older adults who had sarcopenia, reducing the prevalence found for this condition in the group of older adults studied at the LTCF.