4.2.2 Correlation analysis between sleep quality and frailty
In this study, age was found to impact frailty, with the risk of frailty increasing. Sleep quality can be involved as a mediator in age's influence on frailty in middle-aged and elderly residents. Decreased sleep quality linked to the onset of frailty (29), chronic loss of sleep quality negatively affects the immune system(58). In addition, long-term sleep quality decline can limit the activity level of the organism(59), resulting in a decline in physical function(60), which seriously affects physical(61) and mental health(62, 63), significantly reducing the quality of life(64) and greatly increasing the risk of death. Long-term chronic diseases can also lead to declining sleep quality(65), resulting in a vicious circle. Subsequent studies can reduce the incidence of frailty by exploring the relevant factors that affect sleep quality.
4.2.3 Analysis of the correlation between PA and frailty in different occupational characteristics
The results of previous studies suggest that PAL is associated with the occurrence of frailty. However, the present study found no significant correlation between the two, considering that this may be related to the grouping of PAL in this study. The characteristics of PA in occupations such as farmers, where there is a large amount of PA over a long period, are different from the PA based on fitness exercise in previous studies, and exploring the correlation between the total metabolic equivalents and the staging of frailty in different occupations is more likely to illustrate the association between PA and frailty. Therefore, we analyzed the occupations in groups, and the results confirmed the above view. The highest prevalence of frailty was found in the occupations of farmers and laborers, and the relationship between PA and frailty was different from that of the other occupations, probably because of the long periods of heavy PA in both occupations.
In order to further confirm the above conjecture, this study will be divided into two groups based on whether or not the occupations have long-term high levels of PA. It was found that Occupation 1, which has long-term high levels of PA, is more likely to have a pre-frailty period as the intensity of PA reaches its highest value. In contrast, occupation 2 that do not have long periods of high levels of PA are more likely to experience periods of non-frailty as the level of PA increases, which is consistent with the results of previous studies. Nevertheless, regardless of occupation, residents with low PA contribute to the development of frailty. In addition, we have found that the prevalence of the disease is higher in residents with a long history of heavy PA.
The risk of frailty generally decreases with progressively higher levels of PA. However, excessive PA hurts the organism, counteracting the positive effects of PA on the body, and may produce a different developmental trajectory. We have speculated about this. On the one hand, those residents whose own course reversed to a non-frailty stage have progressed to a pre-frailty stage due to the effects of prolonged periods of heavy PA; on the other hand, it is possible that residents in a pre-frailty stage are prevented from reversing to a non-frailty stage due to the long-term effects of the disease. The reasons for this result may be multifaceted, and more longitudinal studies are needed to explore this.
Firstly, PA has different effects on the human body depending on the environment in which it takes place and the way in which it is carried out. PA related to home and physical exercise was associated with a reduced risk of death, and occupational and transportation-related PA was not associated with an adverse risk(66). Additionally, Rachel E. et al(67) study compared different types of PA found that regular fitness exercise reduces the risk of heart disease and that strenuous, heavy, occupational-related physical labor causes arterial stiffness and a negative effect on the nerve. Work-related backbreaking physical work negatively affects arterial stiffness and nerve reflexes, which increases the risk of heart problems; nevertheless, this does not indicate that all work-related PA can harm health, only chronic, strenuous PA can adversely affect the body.
Secondly, with increasing age, significant changes occur in the cardiovascular system of middle-aged and older adults. Thickening and hardening of the aorta and thickening of the ventricular wall due to hypertrophy of the ventricular cells predispose them to increased cardiac load and diminished left ventricular contractile performance(68). The impairment of cardiovascular function is accelerated in middle-aged and older adults under the effect of prolonged high levels of PA. Since cardiovascular disease and frailty have similar inflammatory response mechanisms, it is easier to accelerate the process of frailty development(69).
The reason for the difference between the results of this study and previous studies may also be related to the characteristics of the life of the inhabitants of the area. More than half of the people in the present study work in agriculture. Due to the imperfections in transportation, public fitness facilities, and lack of health care awareness, most residents lack regular PA based on fitness exercises, and the heavy physical labor generated by long-term agriculture produces chronic damage to the body, leading to the onset of frailty. In addition, the occupations of agriculturalists as well as construction workers are characterized by long-term exposure to ultraviolet ray radiation, which can trigger a state of cellular senescence and skin inflammation, stimulate immune senescence as well as degeneration of neighboring cells, and evoke a remodeling of the immune system similar to that of normal aging(70). Some studies have found that long-term occupational exposure to pesticides increases the prevalence of chronic neurological and cardiovascular diseases(71–73), as well as cancer, and even increases the risk of cognition, memory, and the occurrence of psychological distress and suicide in adults(74) and that the gradual accumulation of these adverse effects may lead to the premature onset of frailty. Moreover, the period investigated in this study was from July to August, when local temperatures could reach 40°C or more. The farmers had just finished their heavy agricultural production. PA in hot conditions increases the risk of Exercise Heat Stroke (EHS) (75) and affects β-activities in most areas of the brain(76). The prevalence of negative emotions increases significantly when a person is outdoors in the heat for more than 120 min(77). Older adults with hypertension or diabetes, when physically active for long periods in hot environments, may exhibit tremendous cellular stress, leading to cellular damage(78). Thus, hot weather may have contributed to the higher prevalence of frailty obtained in this study, and considering that the development of frailty is reversible, subsequent studies may consider comparing the changes in prevalence across seasons to confirm the above observation.