Browsing by Author "Rae, Dale"

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    Circadian rhythm, activity level, training habits and sports performance : the molecular and subjective components
    (2013) Stephenson, Kim Jenna; Rae, Dale; Roden, Laura
    Circadian rhythmicity, which is driven by a circadian clock, is a property of a biological process that displays an oscillation of approximately 24-hours even in the absence of external time cues. Individual differences in the preferred times of waking, activity and rest (sleep) are known as chronotype or diurnal preference; which arise due to differences in circadian rhythmicity due to the fact that rhythms are not exactly 24-hours. Various polymorphisms of certain genes involved in circadian rhythm generation have been associated with extreme chronotype. Of interest to this study is the PER3 gene as it has a variable number tandem repeat (VNTR) polymorphism in the coding region, which is repeated either four of five times, encoding proteins of different lengths.
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    Diurnal preference and sports performance : a subjective and genetic view
    (2011) Kunorozva, Lovemore; Roden, Laura; Rae, Dale
    [T]he purpose of this study was to describe the distribution of morning- or evening-preferring individuals (measured using the Horne-Östberg morningness-eveningness personality questionnaire) and PER3 VNTR polymorphism (from genomic DNA products extracted from human buccal cell samples amplified and digested with NcoI) within male Caucasian, trained cyclists (CYC, n=138), Ironman triathletes (IM, n=301) and an active, but non-competitive control population of Caucasian males (CON, n=120). In addition, performance was assessed in trained cyclists strongly preferring mornings or evenings at various times of day.
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    Perceived and objective neighborhood support for outside of school physical activity in South African children
    (BioMed Central, 2016-06-01) Uys, Monika; Broyles, Stephanie T; Draper, Catherine E; Hendricks, Sharief; Rae, Dale; Naidoo, Nirmala; Katzmarzyk, Peter T; Lambert, Estelle V
    Background: The neighborhood environment has the potential to influence children’s participation in physical activity. However, children’s outdoor play is controlled by parents to a great extent. This study aimed to investigate whether parents' perceptions of the neighborhood environment and the objectively measured neighborhood environment were associated with children's moderate-to-vigorous intensity physical activity (MVPA) outside of school hours; and to determine if these perceptions and objective measures of the neighborhood environment differ between high and low socio-economic status (SES) groups. Methods: In total, 258 parents of 9–11 year-old children, recruited from the South African sample of the International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE), completed a questionnaire concerning the family and neighborhood environment. Objective measures of the environment were also obtained using Geographic Information Systems (GIS). Children wore an Actigraph (GT3X+) accelerometer for 7 days to measure levels of MVPA. Multilevel regression models were used to determine the association between the neighborhood environment and MVPA out of school hours. Results: Parents’ perceptions of the neighborhood physical activity facilities were positively associated with children’s MVPA before school (β = 1.50 ± 0.51, p = 0.003). Objective measures of neighborhood safety and traffic risk were associated with children’s after-school MVPA (β = −2.72 ± 1.35, p = 0.044 and β = −2.63 ± 1.26, p = 0.038, respectively). These associations were significant in the low SES group (β = −3.38 ± 1.65, p = 0.040 and β = −3.76 ± 1.61, p = 0.020, respectively), but unrelated to MVPA in the high SES group. Conclusions: This study found that several of the objective measures of the neighborhood environment were significantly associated with children’s outside-of-school MVPA, while most of the parents’ perceptions of the neighborhood environment were unrelated.
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    Physical activity, sedentary behaviour and cardiometabolic disease risk among adults living with obstructive sleep apnoea: Is there a case for exercise as an adjunct therapy?
    (2024) Brand, Batsheva; D'alton, Caroline; Rae, Dale
    Background: Sleep disorders, and resultant poor sleep quality, have emerged as being related to cardiometabolic disease (CMD) risk, including obesity, hypertension, type 2 diabetes mellitus (T2DM), and cardiovascular disease (CVD). Obstructive sleep apnoea (OSA) is the second most common sleep disorder and is characterized by multiple obstructive apnoea episodes (i.e. cessation of breathing due to complete collapse and occlusion of the upper airways), hypopnoea events (i.e. partial collapse and occlusion of the upper airways) and respiratory effort-related arousals during sleep. OSA is diagnosed using an overnight polysomnography (PSG) sleep study. The resultant Apnoea Hypopnoea Index (AHI) is used to determine the severity of OSA and reflects the number of both apnoeic or hypopnoeic events occurring per hour of sleep. Mild OSA is defined as AHI scores of 5-15, moderate OSA by scores of 15-30 and severe OSA by scores ≥30. Given the promising evidence base for the role of exercise as an adjunct therapy for OSA patients, we would ultimately like to design and implement an exercise intervention, particularly in the public healthcare setting in South Africa where access to CPAP therapy is constrained. Due to the paucity of data for patients with OSA in South Africa, we propose the current formative study to first describe OSA severity, CMD risk and habitual physical activity (PA) levels among individuals with OSA. As mentioned above, the primary treatment of OSA is positive airway pressure (PAP) therapy, with CPAP being the most common. This, together with the role of obesity in the disease, has seen the adjuncts such as exercise and dietary interventions become of even greater significance for the clinical management of these individuals living in a low income setting while seeking supportive routes. Therefore, the aim of this study is to compare PA levels, sedentary behaviour, sleep and CMD risk characteristics of adults with OSA (OSA group) to age- and gender-matched adults without OSA (CON group). This will be achieved through three objectives: 1. To systematically review the nature and efficacy of exercise interventions. 2. To characterise the CMD risk profile of both groups utilising anthropometry (BMI, waist circumference), physiological measures (resting BP and HR) and medical history (diagnosed chronic conditions and medication use). 3. To objectively measure and compare PA levels, sedentary behaviour, and habitual sleep patterns between the OSA and CON groups using wrist-worn accelerometery. 4. To explore associations between PA and CMD risk in the OSA and CON groups. Methods: A systematic review was used to assess all current studies evaluating the efficacy of an exercise program on reducing OSA severity and improving subsequent quality of life and minimising cardiometabolic risk factors in patients with OSA (e.g., improving fitness and reducing BMI and daytime sleepiness). In addition, the key components of these exercise interventions (e.g., mode of exercise, duration, frequency, intensity) were analysed on improving health outcomes in OSA patients. The main study included, thirty seven participants placed within one of two groups; the Obstructive Sleep Apnoea (OSA) group comprising of both male and female adults (n=18), previously diagnosed with moderate to severe OSA (AHI>15), and a control (CON) group comprising of both male and female adults (n=19) with no previous diagnosis of OSA nor symptoms or signs of OSA as confirmed on a validated OSA screening questionnaire (STOP-Bang, Chung, 2016), matched to the OSA group for ages (18y to 65y) and sex. Participants were excluded if they were ambulatory (i.e., makes use of any walking aid), reported any recent (2 month) change in their usual PA or sleep habits. Exclusion criteria for the CON group also included (i) a previous diagnosis of OSA (AHI ≥5), (ii) a STOP-Bang score of >4 or (iii) an affirmative answer to the STOP-Bang question. Participants for both groups were recruited from the greater Cape and Johannesburg Metropolitan areas. All participants were informed of the study purpose, risks and benefits and provided written informed consent indicating willingness to take part in the study. This study was approved by the University of Cape Town's Faculty of Health Sciences Human Research Ethics Committee (Ref: 142/2021) and was performed under strict Covid-19 regulations. In this cross-sectional observational study, all participants completed a detailed questionnaire. The investigator measured their weight, height, waist, and neck circumferences, resting BP and HR. Participants were then given a small wrist-worn accelerometer to wear for the next seven days to measure their habitual sleep, PA and sedentary habits and asked to simultaneously complete a sleep and PA diary. They returned the sleep monitor and diary on their second visit to the laboratory eight days later. Results: The present systematic review indicated that PA is an effective intervention in reducing OSA severity, improving cardio-vascular fitness, reducing important cardiometabolic risk factors and quality of life in OSA patients. The optimal combination of aerobic training and resistance exercises could also be better defined to enhance the development of exercise programs in OSA patients. The main finding of this study was that there is a similarity between the total sedentary and light activity counts and hours per day, among the OSA and CON groups, but the key differences lie in the moderate and vigorous PA settings. This suggests that the higher PA level of the CON group, implying that a lower BMI, fewer chronic conditions, and a more acceptable blood pressure reading, are significant factors contributing to their lower incidence of suffering from OSA. Conclusion: The gold standard for OSA treatment is CPAP, which reduces hypoxias. The systematic review indicated that exercise alone gives a limited benefit, (example: reducing BMI). The cardio metabolic system will benefit from effective exercise, but it will not treat OSA, rather reducing the risk of side effects of OSA. In order to optimize risk factor control and reduce long-term morbimortality, there is also a strong need for combined treatment strategies for OSA patients.
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    The role of chronotype in the participation and performance of South African and Dutch marathon runners
    (2014) Henst, Rob; Rae, Dale; Roden, Laura
    Introduction: Our circadian rhythms are internal biological rhythms of approximately (circa) 24 - hours (dies) allowing us to synchronize our internal biological “clock” with external time cues. Many innate biological functions are dependent on time-of-day, such as secreting adrenaline and cortisol in the mornings and melatonin in the evenings. The time-of-day at which these and other physiological functions are active, change or reach a certain level may influence a person’s diurnal preference, i.e. preference for mornings (morning-types) or evenings (evening-types), and is referred to as ‘chronotype’. Many different factors may affect a person’s chronotype, including age, sex, physical activity, ethnicity and geographical location. Certain clock-related genotypes have also been shown to be associated with chronotype. For example, some studies have found that the 5-repeat allele of the PER3 variable number tandem repeat (VNTR) polymorphism (PER35) is associated with a preference for mornings. Recent research has shown a high prevalence of morning-types and PER35VNTR allele carriers in trained South African runners, cyclists and triathletes. It was proposed that the early morning start-times of these endurance events might select people with a preference for mornings, since morning-types may cope better with rising early and being physically active in the early morning. Alternatively, the habitual early waking for training or endurance events may have conditioned the athletes to adapt to become morning-types. However, the geographical location of South Africa (i.e. climate and day length) and the fact that each group was physically active may also have contributed to this finding. Comparison of South African and Dutch runners would allow us to explore the effects of race start time and geography on this observation, since marathons in The Netherlands on average start at 11:41, and since the two countries differ significantly in latitude and as such have noticeable differences in daylight exposure. Aims: The aims of this study were 1) to compare the PER3VNTR genotype and chronotype distribution of South African and Dutch recreational marathon runners and active but non-competitive controls; 2) to investigate the relationship between the PER3VNTR genotype and chronotype in both the Dutch and South African samples; and 3) to determine whether marathon race time is associated with chronotype and PER3VNTR genotype in Dutch and South African marathon Methods: Ninety-five trained South African male marathon runners, 97 South African male active but non-competitive controls, 90 trained Dutch male marathon runners and 98 Dutch male active but non-competitive controls completed a questionnaire capturing demographics, training and race history, including personal best and most recent full and half-marathon race time (if applicable) and the Horne-Östberg morningness-eveningness personality questionnaire (HÖ-MEQ, a tool to assess a person’s chronotype). Each participant provided a buccal cell swab from with total genomic DNA was extracted to determine his PER3VNTR polymorphism genotype. The official race time from each runner who completed the designated marathons in South Africa or the Netherlands was collected from the event websites. Results: The South African and Dutch runners were more morning-orientated than their respective control groups and the South African runners were more morning-orientated than the Dutch runners. The PER3 VNTR polymorphism distribution was similar between the four groups and was not associated with chronotype. The marathon performance of the morning-type South African runners was better than the evening-types, and a higher HÖ-MEQ score (morningness) correlated with better personal best and most recent half-marathon race time. Similar observations were not found in the Dutch runners. Discussion: Since a higher prevalence of morning-types in South African marathon runners compared to Dutch marathon runners was found, it is proposed that the early marathon start-times in South Africa may favour morning-types, who are able to cope with those early morning start times. Alternatively, one could argue that through repetitive early-morning racing (i.e. participating in competitive running events), the chronotype of South African runners may be conditioned to that of a morning-type over time. It is proposed that this ability to cope with early morning marathon start times may lead to better marathon performances for morning-types than neither-types and evening-types in the South African running group. This effect does not occur in the Netherlands, where marathons start later in the morning and do thus not favour a certain chronotype. The difference in daylight exposure between the two countries as a function of latitude does not seem to affect chronotype, since the active but non-competitive control groups did not differ significantly between South Africa and the Netherlands. Unlike the findings from a previous study, the PER35allele was not more prevalent among the South African runners, but rather the distribution wasi n line with what has been described in most, but not all, other populations. No association between the PER35VNTR xpolymorphism and chronotype was found in any of the four groups. Since the four groups investigated in this study comprised physically active individuals, it is proposed that this lack of association may be due to the habituation effects of physical activity and early morning start times of marathon events(for only the South African runners). Conceivably,this habituation may even shift the diurnal preference of those with the PER34/5 and PER34/4VNTR genotypes towards morningness, disassociating any relationship between chronotype and the PER3VNTR genotype. Conclusion: The early morning start time of South African marathon events may favour morning-types, due to their ability to cope with being physically active in the early morning. We propose that the PER3VNTR genotype cannot solely explain the higher prevalence of morning-types in the South African runners in this study, however, it is very likely that the PER3VNTR genotype does play an important role in the chronotype distributions found in the study of Kunorozva et al.(2012). Since the PER3VNTR genotype was not associated with chronotype in any of the four groups, it is proposed that habituation to early-morning marathon racing may be the causal effect of the high number of morning-types in the South African runners group, and the apparent disassociation between chronotype and the PER3VNTR genotype. We also propose that the habituation effect of physical activity and training time-of-day on chronotype in the other groups may dissociate the PER3VNTR genotype with chronotype in a similar manner to which the early-morning start times of South African endurance events dissociates the two. No effect of geographical location on chronotype was found when comparing the Dutch and the South African groups. The morning-orientated South African runners seem to perform better in marathon running than the more evening-orientated runners do, which may be caused by their ability to cope with these early-morning marathon events. Further studies may explore whether marathon performance in later chronotypes can be improved by training-based habituation.
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    Sleep characteristics and cardiometabolic disease risk factors in corporate executives
    (2024) Pienaar, Paula; Rae, Dale; Lambert Vicki
    Hours spent in work and sleep comprise the majority of time in a typical day of working adults. As a result, the workplace is a key setting for public health action. Among working adults, 71% of deaths globally are related to non-communicable diseases (NCDs), most of which are attributed to cardiometabolic diseases (CMD). While there is clear evidence linking short sleep duration with CMD risk in the general population, similar data in a unique subset of the workforce, namely corporate executives, remains largely unexplored. The purpose of this thesis was to investigate the associations between sleep health and CMD risk in corporate executives. A systematic review and meta-analysis examined associations between selfreported sleep duration, all-cause mortality (ACM) and cardiovascular disease mortality (CVDM) in employed adults. Sleeping
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    Sleep under stress: the complex web of fear, hypervigilance and mental health in a low socioeconomic status community in South Africa
    (2025) Correia, Arron Taylor Lund; Rae, Dale; Rauch Laurie; Roden, Laura C
    Introduction: There is a well-established bidirectional relationship between sleep and mental health. Furthermore, low socioeconomic status (SES) environments have been linked to both poorer sleep and mental health, at leastin part due to a lack of perceived safety. Specifically, individuals who feel unsafe or vulnerable in their neighbourhoods may either delay sleep in favour of remaining alert to potential threats or experience hypervigilance throughout the night. This state of hypervigilance is typically characterized by heightened sympathetic nervous system activity and reduced parasympathetic tone, which can be quantified through measures of autonomic nervous system function, such as heart rate variability. Heart rate variability (HRV) is a non-invasive measure of autonomic regulation of the heart which can be divided into time and frequency domain variables. Frequency domain variables are derived from the spectral power of the electrocardiography signal and include very low, low and high frequency power measures (VLF, LF and HF power, respectively). VLF and HF power reflect sympathetic withdrawal and parasympathetic input, respectively while LF is understood to reflect a combination of sympathetic and parasympathetic input. Lower HRV has previously been linked to various mental disorders, including depression and anxiety, and has been included as a contributing factor in the hyperarousal model of insomnia.
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    Sleep, cardiometabolic health, and neurocognitive performance in esports players
    (2024) Kemp, Chadley; Rae, Dale
    Esports players represent a growing and maturing population within the primary demographic of general video gamers, with a proclivity to engage with a high volume (i.e., dose, duration, and frequency) of video gaming activities. Accordingly, esports players are typically characterized by unique behaviors, including prolonged exposure to blue light from electronic screens, extended periods of sedentary behavior, irregular sleep patterns due to late-night matches or competitions, and high levels of stress, all of which may be undertaken to improve or maintain their competitive status. However, the concern is that these behaviors may, in turn, impact esports players' sleep, circadian rhythms, and physical and mental health over time. Despite the growing popularity of esports among adults, few studies have investigated the relationships between sleep, cardiometabolic health, and neurocognitive performance in this population. Specifically, the vast majority of existing research on gaming and health has focused on children and adolescents, leaving a significant gap in our understanding regarding the potential health risks associated with regular high-volume gaming behaviors in adults. Relatedly, adult esports players might also be more vulnerable to the downstream effects of pathological (i.e., prolonged and excessive) gaming behaviors, given their implicit cardiometabolic disease risk susceptibility, which is attributable to aging but also unhealthy lifestyle behaviors and substance addictions like smoking and alcohol. To address the gap in the literature, this thesis aims to investigate the associations between device­derived sleep patterns, white light exposure, cardiometabolic health status, and neurocognitive performance in adult esports players. In addition, the thesis will describe device-derived quantitative doses and 24-hour profile patterns of physical activity and white light exposure in these individuals. The work underlying this thesis is intended to be a stepping stone toward health regulation in gaming and esports, for which motives are to support individual decisions, governments, and policy makers through awareness and by providing evidence-based recommendations to adopt and maintain healthy gaming behaviors to ameliorate chronic health problems.
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    The development of an exercise intervention framework as a modality of treatment for individuals with obstructive sleep apnea, in the South African public healthcare setting
    (2023) Jaffer, Zakirah; Rae, Dale; D'alton Caroline
    Introduction: Obstructive sleep apnoea (OSA) is described as a breathing-related sleep disorder wherein your ventilation is impaired during sleep, due to the narrowing and collapse of the upper airway. Untreated OSA has been shown to increase the number of severe cardiovascular and cerebrovascular events. Common treatment modalities for OSA, including surgical intervention and continuous positive airway pressure therapy are effective but remain extremely expensive. It is thus often inaccessible to those in a low-income, under-resourced setting, or those without access to healthcare, as is the case for the majority of South Africans. Since addressing weight loss is a key component of OSA treatment, exercise may provide the benefits of addressing both weight loss and inflammation in OSA patients, as well as lowering the risk of cardiovascular disease, depression, and comorbidities that arise from obesity. Aims: The aims of this study were to understand the nature of, and perception to, current physical activity (PA) habits as well as barriers to exercise, faced by individuals with obstructive sleep apnoea (OSA group) compared to a control group of individuals without OSA (CON group). This information was then used to design an exercise intervention framework for OSA patients which can be implemented in an under-resourced setting, such as in the public healthcare system in South Africa. Methods: This is a secondary analysis of data already collected as part of a larger study investigating “Physical activity and sedentary behavior among patients with obstructive sleep apnoea in South Africa” (HREC Ref: 142/2021). The parent observational study made use of custom and validated questionnaires answered by adults diagnosed with moderate to severe OSA and control participants with no OSA. Participants were asked to report on current and past exercise habits, perceptions, enablers, and barriers to PA, as well as preferred modes of exercise, which were further analyzed. Results: A total of thirty-seven adults were included in the current study; eighteen of whom had been diagnosed with OSA, matched with nineteen CON adults for age, BMI, neck circumference, waist circumference, and blood pressure (all p>0.050). Self-reported current participation in PA was lower in the OSA group (61%) compared to the CON group (74%), although not significantly different (p=0.410), with lower levels of PA between the two groups reported as being due to time constraints, dark/unsafe environment, laziness, covid restrictions, a lack of interest, motivation, and illness/injury/surgery within the OSA group specifically, There was a high presence of structural pain within the OSA group (83%) compared to the CON group (58%), although not significantly different (0.091), which was aggravated by PA (33% and 36% respectively). Frequency of PA was most commonly recorded as four to seven days per week by both the CON and OSA group (p=0.975, with a self-reported medium intensity ranging between 4-7 out of 10 (p=0.281) based on a subjectively designed 10-point scale (1: very low intensity, 10: very high intensity). Walking was the preferred form of PA within the OSA group (72%), as well as within the CON group (63%) (p=0.556), and both groups identified the ‘lack of motivation' as a barrier to participation in PA (p=1.000). Conclusion: Taking into account the observations 7 from evidence-based reviews in Chapter 1 and the results from Chapter 2, the proposed framework should include an exercise intervention that considers a moderate frequency of three to five times/week, a medium and building up to a higher intensity of 40-80% HRR, shorter sessions of 25-40 minutes per session but building up to 60 minutes where possible, and inclusion of aerobic and resistance exercises with a focus on walking as well as lower body activities. Group sessions should be considered to allow space for social interactions through physical activity which may help work around the barrier of motivation. Patient education on OSA and its consequences, the role of sleep, sleep hygiene, and disease management should also be included as part of the exercise intervention. Importantly, our results provide a basis for further development on this framework to establish an exercise Intervention as an adjunct therapy for OSA patients, specifically in lower income settings. Future studies can explore the efficacy of these exercise interventions in the management of OSA in adults from low income settings.
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    Towards an understanding of the relationship between sleep and cardiovascular disease risk in adults of African descent living in a low socioeconomic status community
    (2025) Forshaw, Philippa; Rae, Dale; Roden, Laura; Lambert, Estelle
    Background: Individuals of African descent, specifically African Americans and those from Sub-Saharan Africa, experience a higher burden of cardiovascular disease (CVD) and its associated risk factors (such as obesity, diabetes and hypertension) as well as shorter, poorer sleep quality, compared to Caucasian American individuals. Blood pressure (BP) non-dipping (i.e. the failure of BP to decrease at night during sleep) and nocturnal hypertension are important markers of CVD risk and are substantially more prevalent in African American, compared to Caucasian American, individuals. Two additional layers that need consideration are socioeconomic status (SES) and sex. In contrast to much of the research in the Global North predominantly demonstrating shorter objective and subjective sleep durations (around 6- 7h per night) among African descended individuals living in low SES environments, South Africans of African descent living in low SES communities report much longer sleep durations, around 8-10h per night. Thus, while on one hand, lower SES has been associated with higher risk for CVD possibly through shorter sleep, the nature of the relationship between long sleep duration and CVD risk in the South African context is not well understood. Given the significant sex-specific differences in both CVD risk and sleep, there is a need for research focused on understanding sex-specific associations between CVD and sleep health. Thus, the purpose of this thesis was to investigate sex-specific relationships between CVD risk, nocturnal BP and sleep health in adults of African descent living in a low SES community in South Africa. This purpose was achieved through the following aims: i) to investigate sex-specific relationships between self-reported sleep characteristics and CVD risk among individuals of African descent living in a low SES community, ii) to investigate sex-specific relationships between actigraphy-derived sleep characteristics and CVD risk in these same individuals, iii) to systematically review the literature on sleep and BP dipping in apparently healthy individuals, iv) to explore sex-specific associations between actigraphy-derived sleep characteristics, nocturnal BP and CVD risk among adults of African descent living in a low SES community and v) to conduct qualitative interviews with these same individuals to explore how external (e.g. environmental barriers to and promoters of good sleep) and internal (e.g. individual knowledge, attitudes, beliefs and perceptions around sleep) factors might impact sleep health. This thesis explored the hypothesis that adverse environmental conditions associated with living in low SES communities are not conducive to healthy sleep, driving BP non-dipping, nocturnal hypertension and higher CVD risk. Methods: For Chapters 2 and 3, individuals of African descent (56% women, 29-51y, 40% employed) living in Khayelitsha (an informal settlement in South Africa characterised by high rates of crime, violence and poverty) were recruited and studied. Sleep characteristics were measured subjectively using self-reported questionnaires (Pittsburgh Sleep Quality Index (PSQI), Epworth Sleepiness Scale (ESS), Insomnia Severity Index (ISI); n=412) and objectively with seven days of wrist-worn actigraphy (n=194). CVD risk was assessed using the body mass index (BMI)-modified Framingham 10-year CVD risk score and clinical measures (BMI, waist circumference, resting BP, fasting glucose). We then conducted a systematic review (Chapter 4) exploring associations between BP dipping and sleep in healthy individuals. In Chapter 5 we measured twenty-four hour ambulatory BP in a sub-set of individuals from the original cohort (n=59) to explore associations between BP dipping, nocturnal hypertension, sleep characteristics and CVD risk scores. Finally, we conducted one-on-one qualitative interviews (Chapter 6) in a further sub-set of participants (n=15) to explore possible external (e.g. environmental barriers to and promoters of good sleep) and internal (e.g. individual knowledge, attitudes, beliefs and perceptions around sleep) factors related to sleep health in this population.Results: When we examined associations between subjectively measured sleep and CVD risk (Chapter 2), found that men (n=178) reporting poor sleep quality (PSQI>5, OR: 1.95, 95%CI: 1.07, 3.51, p=0.025) and earlier bedtimes (OR: 0.54, 95%CI: 0.39, 0.74, p<0.001)were more likely to have higher CVD risk scores. Women (n=234) reporting earlier bedtimes (OR: 0.72, 95%CI: 0.55, 0.95, p=0.020) and wake-up times (OR: 0.30, 95%CI: 0.13, 0.73, p=0.007), longer sleep onset latencies (OR: 1.47, 95%CI: 1.43, 1.88, p=0.003), shorter total sleep times (OR: 0.84, 95%CI: 0.72, 0.98, p=0.029), higher PSQI global scores (OR: 1.93, 95%CI: 1.29, 2.90, p=0.001) and more moderate to severe insomnia symptoms (ISI≥15, OR: 3.24, 95%CI: 1.04, 10.04, p=0.042) were more likely to have higher CVD risk scores. We confirm actigraphy derived long (men: 9.4 ± 1.4h, women: 8.9 ± 1.2h) but disturbed sleep (low sleep efficiencies [men: 81.8 (76.8, 85.7)%), women: 79.9 (72.5, 84.6)%], high sleep fragmentation indices [men: 58.3 (52.5, 65.2)%, women: 63.4 (56.3, 68.2)%] and high wake after sleep onset (WASO) times [men: 103.1 (76.1, 127.0)min, women: 84.9 (68.8, 110.4)min]) in this population, for whom obesity (specifically among women: 60.3%) and hypertension (men: 48%, women: 44%) are prevalent. Associations between actigraphy-derived sleep measures and CVD risk (Chapter 3) found that among men (n=94), earlier midsleep time was associated with higher CVD risk scores (b =–0.17, 95%CI:–0.33, –0.02, p=0.030) while shorter sleep duration was associated with obesity (OR: 0.48, 95%CI: 0.25, 0.90, p=0.023). Among women (n=100), earlier wake-up times (b: –0.24, 95%CI: –0.41, –0.07, p=0.007) and midsleep times (b: – 0.18, 95%CI: –0.39, 0.00, p=0.046) were associated with higher CVD risk scores. Women with earlier bedtimes (OR: 0.53, 95%CI: 0.33, 0.85, p=0.009) and midsleep times (OR: 0.47, 95%CI: 0.26, 0.83, p=0.010) were more likely to have elevated BP, and those with earlier wake-up times (OR: 0.54, 95%CI: 0.35, 0.81, p=0.003) and midsleep times (OR: 0.46, 95%CI: 0.27, 0.77, p=0.003) were also more likely to be obese. Interaction effects revealed that among women, CVD risk scores were higher in those who had shorter sleep combined with later bedtimes or in those who had longer sleep combined with earlier bedtimes (β:–2.38, 95%CI: –0.35, –0.12, p<0.001). A weaker interaction effect was found for WASO such that CVD risk score was higher in women with longer sleep and more WASO or shorter sleep with less WASO (β: 0.004, 95%CI: 0.00, 0.00, p=0.014). The systematic review (Chapter 4) showed that BP non dipping in apparently healthy individuals was associated with short sleep duration, more sleep fragmentation, less sleep depth and increased variability in sleep timing. Measuring 24h ambulatory BP (Chapter 5) found a high proportion of SBP non-dipping (men: 50%, women: 61%), with 48% of men and 72% of women also presenting with nocturnal hypertension. Among the women (n=36), shorter total sleep times (rho: 0.42, p=0.020) and worse sleep efficiencies (rho: 0.51, p=0.003) were correlated with smaller SBP dipping percentages. Similarly, shorter sleep durations (rho: 0.39, p=0.029), shorter total sleep times (rho: 0.44, p=0.014) and worse sleep efficiencies (rho: 0.37, p=0.037) were correlated with smaller DBP dipping percentages. Women with worse sleep efficiencies (rho: –0.39, p=0.016) has higher nocturnal SBP. Among the men (n=23), worse sleep efficiencies (SBP rho: –0.47, p=0.024; DBP rho: – 0.50, p=0.015), greater WASO (SBP rho: 0.59, p=0.003; DBP rho: 0.50, p=0.014) and greater sleep fragmentation indices (SBP rho: 0.59, p=0.003; DBP rho: 0.59, p=0.003) were correlated with higher nocturnal SBP and DBP. Worse sleep duration regularity scores were correlated with lower SBP (rho: – 0.48, p=0.025) and DBP (rho: –0.52, p=0.013) dipping percentages. Men with nocturnal hypertension had higher WASO (116.8 (88.8, 163.3)min vs. 88.1 (65.1, 98.3)min, p=0.031) and sleep fragmentation indices (36.4(33.4, 40.8)% vs. 29.6(25.8, 34.7)%, p=0.019) compared to those without nocturnal hypertension. Insights from the qualitative interviews (Chapter 6) revealed that external factors such as high-density living, noise, crime, violence and excessive alcohol use within the community primarily contributed to disturbing the sleep of participants. Conclusions: This thesis provides new insights, from a Global South lens, to relationships between sleep and cardiovascular health as they relate to adults of African descent living in a low SES environment. 4 Two main features of sleep emerge as important risk factors for CVD in these study participants: mistimed sleep and disturbed sleep, despite adequate sleep opportunities. By considering the lived experiences of individuals in this low SES community, we gained an understanding of the major role that the adverse conditions of the neighbourhood has on impairing sleep health in this population. We speculate that this earlier timed sleep observed predominantly in women, but to some extent in men, might be a direct consequence of environment-related fear, prompting residents to seek refuge in bed at a time which may be too early, potentially contributing to circadian misalignment, which in turn may increase CVD risk. We further hypothesise that when faced with these adverse neighbourhood conditions, some residents may be in a state of hypervigilance at night, resulting in insufficient sympathetic nervous system (SNS) withdrawal, which in turn leads to disturbed sleep. Disturbed sleep may contribute to BP non-dipping or nocturnal hypertension, which may subsequently increase CVD risk, potentially through insufficient cardiovascular system recovery at night. Interestingly, we note that some participants appear to demonstrate resilience through attaining healthy sleep despite living in a challenging neighbourhood environment. Perhaps these are the individuals in whom appropriate SNS withdrawal takes place at night, improving their sleep health and reducing their CVD risk. Considering all the evidence generated though these studies, this thesis proposes the term Sleep Health Insecurity - a lack of regular access to healthy sleep (that which is of sufficient duration, regular, appropriately timed, consolidated, satisfying and refreshing), which is essential for optimal mental and physical health, emotional well-being and cognition. Although we propose that residents of Khayelitsha are experiencing Sleep Health Insecurity, which may increase their CVD risk, these residents likely represent not only a large sector of the South African population but also other similar low SES populations around the world, making this concept a fundamental global health issue.