Aerobic exercise modulates cytokine profile and sleep quality in elderly

Background Sleep disturbance is a major problem for older adults which can be exacerbated by increased inflammation as aging is associated with increased circulating pro-inflammatory and lower anti-inflammatory cytokines. There is a need to develop alternative medicine techniques to help improve sleep quality in the elderly. Objective To investigate the effects of aerobic exercise training on the sleep quality and inflammatory cytokines in elderly subjects. Material and methods Forty previously sedentary elderly subjects participated in this study, their age ranged from 61- 67 years. All subjects were randomly assigned to supervised aerobic exercise intervention group (group A, n=25) or control group (group B, n=25). Polysomnographic recordings for sleep quality assessment, interleukin- 6 (IL-6), tumor necrosis factor- alpha (TNF-α) and interleukin-10 (IL-10) were measured before and after 6 months at the end of the study. Results There was a significant increase in total sleep duration, sleep efficiency and sleep onset latency in group(A) after 6 months of aerobic exercise training, while, wake time after sleep onset and rapid eye movement (REM) latency significantly reduced after 6 months of aerobic training compared with values obtained prior to aerobic exercise training. Also, the mean values of TNF- α and IL-6 decreased significantly and the mean value of IL-10 significantly increased in group (A) after the aerobic exercise training, however the results of the control group were not significant. Moreover, there were significant differences between both groups at the end of the study. Conclusion Exercise training can be considered as a non-pharmacological modality for modifying sleep quality and inflammation among elderly.


Introduction
Aging sleep disturbance is a common problem reported by 39-75% of older persons 1,2 . Sleep disturbance may result in fatigue, emotional distress, difficulty with concentration and memory, daytime dysfunction and an increased risk of falls; it has a negative impact on morbidity, mortality and quality of life 3,4 . However, sleep disturbance is not an inevitable part of aging 3 . The most frequent changes in sleep caused by aging are increases in the frequency nighttime awakenings and arousals and a decrease in the time spent in deep sleep 5 . Additional changes in sleep can also include increases in stages 1 and 2 sleep time, decreases in stages 3 and 4 sleep time, decreases in rapid eye movement (REM) sleep, increases in sleep fragmentation, decreases in total sleep time, decreases in sleep efficiency and increases in sleep disturbances [5][6][7] .
low-grade systemic inflammation present in older individuals 8,9 . Indeed, this age-dependent pro-inflammatory state may be associated with several pathophysiological conditions associated with sleep complaints 10 , such as sleep disturbance [11][12][13] , in addition to many other age-related diseases, such as arteriosclerosis, dementia, osteoporosis, cancer 14 and obesity 15 . Taken together, these factors can contribute to a poor quality of life for elderly individuals.
Because sleep complaints and sleep-related problems increase with age, it is possible that they are promoted by low-grade systemic inflammation present in older individuals 16 . Indeed, this age-dependent pro-inflammatory state may be associated with several pathophysiological conditions associated with sleep complaints 17 , such as sleep disturbance 18,19 Sleep disturbance should be recognized and managed with either pharmacological or non-pharmacological treatment. Lower physical activity level was found to be a significant risk factor for insomnia 20 . Previous studies have reported that moderate-intensity exercise, such as Tai Chi or yoga may improve sleep quality [21][22][23] . In addition, participation in a regular exercise program can also have positive effects on sleep quality 24 , mood 25 , and cognitive abilities 26 . A meta-analysis of 12 studies indicates that regular exercise increases total sleep time 27 . In addition, epidemiological data based on self-reports consistently support the view that acute and chronic exercise promotes sleep 28 .
Most studies examining the effects of exercise on sleep have focused on young good sleepers or fit athletes 28,29 . The limited data available in older adults also indicate an association between physical activity levels and sleep quality 30 . There is also evidence that increasing physical activity level can improve sleep quality in older adults 30,31 . For example, in sedentary older adults, a 16 week program of mild to moderate intense physical activity improved self-rated sleep quality 24 . In another study, exposure to daily physical and social activity for just 2 weeks also had positive effects on sleep quality in older adults 32 . Furthermore, in older adults with depression, progressive weight training significantly improved measures of both subjective sleep quality and depression 25 . Moreover, moderate training may reduce resting plasma concentrations of pro-inflammatory cytokines and increase anti-inflammatory cytokines, consequently improving the quality of sleep 18 .
The aim of the study was to investigate the effect of aerobic exercise training on the sleep quality and inflammatory cytokines in elderly subjects.

Patients and methods Subjects
Fifty healthy community dwelling sedentary men and women who were 61 years or older with symptoms of difficulty falling asleep and/or staying asleep, given theopportunity to sleep, accompanied by impairment in daytime functioning for at least 3 months. In addition, participants were required to be independent in activities of daily living and without significant cognitive deficits and have a sleep efficiency (SE) less than 80% and/or awaken earlier than desired if before 6 AM and a total sleep time of less than 6.5 hours; Also, sedentary, defined as participation in exercise of mild to moderate intensity for less than 30 min per day and less than 2 times per week on a regular basis. Exclusion criteria included history of major psychiatric disorder as mania or alcohol or substance abuse or other neurological disorders, significant depressive symptoms, serious medical conditions or cardiopulmonary disease that contraindicate exercise, current use or use within the past month of psychoactive, hypnotic, stimulant or analgesic medications, shift work or other types of self-imposed irregular sleep schedules, smoking or caffeine consumption greater than 300 mg per day. This study used a randomized parallel pre-post design. Participants were randomly assigned to either an aerobic exercise intervention group (group A) who participated in the exercise intervention conducted 3 times per week for 6 months or non-physical activity intervention and control group(group B) who received no training intervention and asked to follow their usual life style. This study was approved by the Ethical Committee for Scientific Research, Faculty of Applied Medical Sciences, King Abdulaziz University. All participants provided written informed consent.

Measurements and procedures A. Sleep measures:
All participants underwent polysomnographic (PSG) recording before and after the exercise training. For the pre-intervention assessment, PSG recording was performed over 2 nights. The first night served as an adaption night; 48 hour later, the participants returned for another night of PSG recording. B. Inflammatory cytokines assessment: Blood samples were collected from the antecubital vein after a 12hour fasting, the blood samples were centrifuged at + 4 °C (1000 = g for 10 min). Interleukin-6 (IL-6) and Interleukin-10 (IL-10) levels were analyzed by "Immulite 2000"immunassay analyzer (Siemens Healthcare Diagnostics, Deerfield, USA). However, tumor necrosis factor-alpha (TNF-α) was measured by ELISA kits (ELX 50) in addition to ELISA microplate reader (ELX 808; BioTek Instruments, USA).
C. Aerobic exercise training program: Patients in group (A) were submitted to a 40 min aerobic session on a treadmill (the initial, 5-minute warm-up phase performed on the treadmill at a low load, each training session lasted 30 minutes and ended with 5-minute recovery and relaxation phase) either walking or running, based on heart rate, until the target heart rate was reached, according to American College of Sport Medicine guidelines. The program began with 10 min of stretching and was conducted using the maximal heart rate index (HRmax) estimated by: 220-age. First 2 months = 60-70% of HRmax, second 4 months = 70-80% of HRmax34.

Statistical analysis
The mean values of the investigated parameters obtained before and after six months in both groups were compared using paired "t" test. Independent "t" test was used for the comparison between the two groups (P<0.05).

Results
The two groups were considered homogeneous regarding the demographic variables. The mean age of the group (A) was 64. 98 ± 4.15years, and the mean age of group (B) was 65.72 ± 3.86years. There was no significant differences in age, weight, height, body mass index (BMI), waist circumference, hip circumference, systolic blood pressure and diastolic blood pressurebetween both groups (figure 1).

Figure (1):
Baseline characteristics of study participants. Regarding sleep quality parameter, there was a significantincrease in the total sleep duration, Sleep efficiency and Sleep onset latency in group(A) after 6 months of aero-bic exercise training, while, awake time after sleep onset and REM latency significantly reduced after 6 months of aerobic training compared with values obtained prior to aerobic exercise training (table 1).  however the results of the control group were not significant (table 2). Also, there were significant differences between both groups at the end of the study (table 3).
Moreover, the mean values of TNF-α and IL-6 decreased significantly and the mean value of IL-10 significantly increased in group (A) after the aerobic exercise training, Table 2: Mean value and significance of polysomnographic parameters, TNF-α, IL-6 and IL-10 in group (B) before and at the end of the study. REM: rapid eye movements; TNF-α: tumor necrosis factor -alpha; IL-6: Interleukin-6; IL-10: Interleukin-10. Table 3: Mean value and significance of polysomnographic parameters, TNF-α, IL-6 and IL-10 in group (A) and group (B) at the end of the study. REM: rapid eye movements; TNF-α: tumor necrosis factor -alpha; IL-6: Interleukin-6; IL-10: Interleukin-10; (*) indicates a significant difference between the two groups, P < 0.05.

Discussion
Aging sleep disorder is an increasingly prevalent serious problem that affects more than 20% and 30%, if older adults in western countries 35 . Lack of sleep can affect an individual's quality of life, social interaction and mood 36 . To date, the most common treatments for sleep disorders remain pharmacological agents as several systematic reviews have reported that hypnotics improve sleep quality [37][38][39] . However, the increased risk of adverse events was found to be statistically significant and poses potential risks for older individuals for falls or cognitive impairment 39 . Although research has found that pharmacological treatment appears an effective treatment for sleep disorders, evidence of its sustained efficacy is lacking 40 . Moreover, non-pharmacological approaches have a long history of treating sleep disorders, among which physical exercise is increasingly regarded as an effective way 41,42 . Concerning sleep quality parameter, there was a significant increase in the total sleep duration, sleep efficiency and sleep onset latency in group (A) after 6 months of aerobic exercise training, while, awake time after sleep onset and REM latency significantly reduced after 6 months of aerobic training compared with values obtained prior to aerobic exercise training (table 2), these results are in line with many previous studies 43-53 .

Reid et al. had Seventeen sedentary elderly subjects with
insomnia who had 16 weeks of aerobic physical activity. The clearly stated that physical activity improved sleep quality on the global Pittsburgh Sleep Quality Index (PSQI) score, sleep latency, sleep duration, daytime dysfunction and sleep efficiency 43 . Where, Lira et al. conducted a study on fourteen male sedentary, healthy, elderly volunteers performed moderate training for 60 minutes/ day, 3 days/week for 24 week at a work rate equivalent to the ventilatory aerobic threshold. They proved that sleep parameters, awake time and REM sleep latency were decreased after 6 months exercise training in relation baseline values 44 . In addition, Yang and colleagues completed a systematic review with meta-analysis of six randomized trials and provided data on 305 participants (241 female). Each of the studies examined an exercise training program that consisted of either moderate intensity aerobic exercise or high intensity resistance exercise. The duration of most of the training programs was between 10 and 16 weeks. All of the studies used the self-reported Pittsburgh Sleep Quality Index to assess sleepquality.
Compared to the control group, the exercise group had significantly reduced sleep latency and medication use 45 . While, Chen and coworkers enrolled twenty-seven participants in 12 weeks of Baduanjin exercise training, they showed that overall sleep quality, subjective sleep quality, sleep latency, sleep duration, sleep efficiency, and daytime dysfunction significantly improved after 12 weeks of intervention 46 . In addition, Santos et al. had twenty-two male, sedentary, healthy, elderly volunteers performed moderate training for 60 min/day, 3 days/week for 24 week at a work rate equivalent to their ventilatory aerobic threshold, their findings suggest that aerobic exercise training increased aerobic capacity parameters, decreased REM latency and decreased time awake 47 . Moreover, Passos and colleagues concluded that a 4-month intervention of moderate aerobic exercise delivered to twenty-one sedentary participants with chronic primary insomnia had polysomnographic data significantly improvements following exercise training, where total sleep time, sleep efficiency and rapid eye movements significantly increased. In addition, sleep onset latency and wake time after sleep onset significantly decreased following exercise training 48 . Regarding the mechanism underlying the effect of exercise on sleep, although the mechanisms by which training can improve sleep quality are not well understood. It has been proposed that exercise training improves sleep quality through increasing energy consumption, endorphin secretion, or body temperature in a manner that facilitates sleep for recuperation of the body [49][50][51] . Moreover, moderate training may reduce resting plasma concentrations of pro-inflammatory cytokines and increase anti-inflammatory cytokines, consequently improving the quality of sleep 52,53 .
Our results demonstrate that aerobic exercise training causes reduction in TNF-α and IL-6 levels, in addition to increase in IL-10 level which suggests that exercise training can reduce inflammation in elderly individuals with more significant changes following aerobic exercise training. Regarding the aerobic exercise training, our results agreed with several studies have shown that aerobic exercise promotes the modulation of inflammation [54][55][56] . Several large cohort studies have found a relationship between self-reported physical activity levels and systemic markers of inflammation: higher levels of physical activity are coupled to lower levels of circulating inflammatory markers in elderly individuals [57][58][59]  showed that regular aerobic exercise training was efficient in lowering IL-6 levels even without weight loss 60 . However, Kohut et al. reported that 10-months of aerobic exercise significantly reduces serum inflammatory mediators in older adults 61 . In addition, Bote et al. demonstrated that 8-months (2 sessions/week, 60-min/session) of aquatic-based exercise training tempered neutrophil activation (chemotaxis) and decreased systemic levels of IL-8 and noradrenalin compared to controls 62 . In addition, Ploeger et al. who reported that moderate aerobic exercise training has been recommended as an anti-inflammatory therapy 63 . Where, Gatta and co-workers examined the expression of cytokines at both rest and following a bout of isokinetic exercise performed before and after 12 weeks of resistance exercise training in 8 young and 8 elderly. They stated that expression of pro-inflammatory cytokines MCP-1, IL-8 and IL-6 increased substantially after acute exercise. By contrast, the expression of the anti-inflammatory cytokines IL-4, IL-10 and IL-13 increased only slightly (or not at all) after acute exercise. These responses were not significantly different between young and elderly men, either before or after 12 weeks of exercise training. They concluded that, regular exercise training might help to normalize this inflammatory response in the elderly 64 . Moreover, Santos et al. stated the levels of IL-6 and TNF-α and the ratio of TNF-α/IL-10 were decreased, whereas IL-10 levels were increased after 24 weeks moderate aerobic training. 47 The three possible mechanisms of exercise anti-inflammatory effects include reduction in visceral fat mass65; reduction in the circulating numbers of pro-inflammatory monocytes 66 and an increase in the circulating numbers of regulatory T cells 67 . Moreover, Hong and colleagues show that cardiorespiratory fitness is associated with reduced low grade inflammation that may in part be mediated by enhancing the ability of immune cells to suppress inflammatory responses via adrenergic receptors 68 . The training-induced sleep changes associated with an improvement in the inflammatory profile, demonstrated by a significant decrease in the level of inflammatory cytokines which were sufficient to improve global sleep phases as older individuals may demonstrate elevated inflammatory cytokines concentrations, which can increase non-rapid eye movement (NREM) sleep by impairing a subset of sleep-related neurons in the preoptic area/basal forebrain 18,19,69 .
The current study has important strengths and limitations. The major strength is the supervised nature of the study. All exercise sessions were supervised essentially 100%. Moreover, the study was randomized; hence, we can extrapolate adherence to the general population. In the other hand, the major limitations is only elderly enrolled in the study, so the value of this study only related to this age group , also small sample size in both groups may limit the possibility of generalization of the findings in the present study. Finally, within the limit of this study, exercise training is recommended for improving sleep quality and modulation of low grade systemic inflammation among elderly. Further researches is needed to explore the impact of other therapeutic modalities on quality of sleep and other biochemical parameters among elderly.

Conclusion
Exercise training can be considered as a non-pharmacological modality for modifying sleep quality and inflammation among elderly.