Persistent deviation from 7 to 8 hours of nightly sleep appears to contribute to the development of cardiovascular disease (CVD) and other related metabolic conditions, including obesity and type 2 diabetes mellitus.1 Studies have often focused on the effect of short sleep duration (<7 hours/night)1 or sleep disorders (particularly obstructive sleep apnea)2 on CVD and other cardiometabolic conditions. However, emerging research suggests that both short-sleep duration and long-sleep duration (typically defined at >8 or 9 h of sleep/night) are associated with increased incidence of CVD.3 Short- and long-sleep duration and poor sleep quality have also been associated with subclinical CVD measures, including coronary artery calcium, carotid intima-media thickness, endothelial and microvascular function, and arterial stiffness.4 Furthermore, short- and long-sleep duration have been associated with increased risk for all-cause mortality,5 with the greater the deviation, the greater the risk of all-cause mortality.3 There is evidence that treatment of a sleep disorder may prevent subsequent cardiovascular events,6 which leads to the possibility that promotion of optimal sleep and the identification and treatment of sleep disorders earlier in life may prevent or reduce the risk of the development of CVD and the subsequent consequence of CVD.
According to the Office of Disease Prevention and Health Promotion,7 social determinants of health (SDOH) are the social factors and physical conditions of the environment in which people are “born, live, learn, work, play, worship, and age.” Social determinants of health have a profound effect on access to preventative health care, health outcomes, quality of life, morbidity, and mortality. Social determinants of health also affect sleep duration and quality, which may in turn contribute to poorer health and well-being,8,9 including poorer cardiovascular health.10,11 Some examples of SDOH that appear to affect sleep are race, ethnicity, socioeconomic status (SES), neighborhood safety, light exposure, and exposure to media and technology. Providing sleep health promotion techniques without considering the SDOH that affect sleep health is remiss and shortsighted.
The Social–Ecological Model (SEM) is a theory-based framework developed to describe the complex and multifaceted ways that behaviors are influenced at an individual, social, and society level. Grandner12 proposed the SEM to consider how social interactions and society influence individuals at a personal level, affecting sleep duration and quality (Fig. 1). An individual's genetics influence their sleep as certain genes have been associated with insomnia,13 for example. Also, an individual's belief that they can function on little sleep or their behaviors of frequently napping in the afternoon or doing activities other than sleeping in their bed, for example, will also affect their sleep duration and quality. The individual factors are imbedded within a social structure that the individual is a member of which influences the individual factors. For example, the individual may live in a neighborhood that is unsafe, noisy, or has nighttime light pollution that contributes to sleep insufficiency. Another example, if the bus line for transportation to get to and from work requires that the person get up early to catch the bus, that may also reduce sleep health. A third example is that the home may not have sufficient bedrooms for an individual to sleep in their own room or there may not be sufficient beds for individuals to have their own bed, and their sleep may be disrupted from sharing a bed or room. The social level factors are in turn embedded in societal level factors, which include technology, media, public policy, and our now active 24 hours a day/7 days a week society. An example of how society influence sleep health is the invention of the light bulb. Before the invention of the light bulb, individuals and families tended to go to sleep when the sun went down and woke up when the sun rose. With the invention of the light bulb, people can be awake and “productive” at all hours of the night. People can work second and third shift during the evening and night. Also, technology allows us to be connected 24 hours a day and exposes our retinas to blue light, which is particularly disruptive for sleep and the circadian rhythm. The individual, social, and societal level factors can directly affect adverse health outcomes. They are also mediated by their influence on sleep which in turns contributes to adverse health outcomes (Fig. 1). Social determinants of health at all levels of the SEM must be considered to influence sleep health and other health outcomes.
Race/ethnicity is one factor (or set of factors) that may affect sleep health. Previous studies have suggested that the racial/ethnic minorities are more likely to experience sleep disturbances and sleep patterns that are associated with adverse health outcomes.14–18 A study by Whinnery et al14 analyzed data from a national survey of nearly 5000 individuals to examine the association between race/ethnicity and 3 categories of sleep: (1) very short sleep of <5 hours, (2) short sleep of 5 to 6 hours, and (3) long sleep of ≥9 hours. After controlling for age, sex, marital status, immigration status, income, education, private insurance, household food security, and general health, black/African Americans were almost 2.5 times as likely to be very short sleepers and nearly 2 times as likely to be short sleepers compared with non-Hispanics white who served as the reference group. They also found that non-Mexican Hispanics/Latinos were approximately 2.7 times as likely to be very short sleepers. In addition, Asians and others were 4 times as likely to be very short sleepers and twice as likely to be short sleepers. This study and others15–19 illustrate that minority status is directly associated with shorter sleep duration, increased sleep disturbances, and increased sleep disordered breathing, which could be significantly affecting and contributing to adverse health outcomes.
In addition to race/ethnicity and SES has been shown to be associated with sleep duration and quality. Education, income, employment status, insurance type, and food security are all aspects of SES that are related to sleep health.9 In one study,14 respondents who did not complete college were more likely to report <5 hours and 5 to 6 hours of sleep compared with college graduates. Also, respondents earning <$75,000/year reported more very short sleep duration. Interestingly, respondents reporting public insurance were more likely to report very short and long sleep duration compared with those reported being uninsured. Also, respondents with very low food security were more likely to report <5 hours and 5 to 6 hours of sleep. This work suggests a direct relationship between SES and sleep health. The authors suggest that “sleep may be conceptualized not only as a marker of socioeconomic disadvantage, but also of psychosocial and/or emotional stressors associated with minority status and/or socioeconomic disadvantage, which also strongly related to negative health outcomes.”14
The physical and social environments are additional factors that influence sleep health and are also associated with race/ethnicity and SES. The physical and social environment consists of many levels from the perhaps more obvious environment of the bedroom and home and extending to the neighborhood and then to the state and country. At the bedroom level, sharing a bed is negatively associated with sleep quality.20 At the household level, an increased household size is associated with insufficient sleep.21 If there are more people in your house and/or you are sharing a bedroom, there may be more noise or light that interfere with sleep. Those with children are well aware that taking care of infants or young children interferes with sleep. A recently published study reports that mothers and fathers experience disrupted sleep even 6 years following the birth of a child.22 Also, being a caregiver for a spouse23,24 or parent can interfere with sleep as does living with someone who works long hours or shift work.25
Neighborhood factors also contribute to sleep disparities,26 likely through chronic activation of the stress pathways that increases risk of CVD.27,28 Hale et al29 found that neighborhood disorder (which is a measure of the degree to which the neighborhood is perceived as noisy, dirty, and crime ridden) was associated with poorer self-reported physical health and that association was mediated by lower sleep quality even after controlling for a variety of sociodemographic factors. Another study by Hale et al30 found that sleep quality explained approximately 20% of the association between neighborhood disorder and self-rated health and depression. Furthermore, for every 1 standard deviation higher on a score of neighborhood social cohesion and neighborhood safety, sleep duration increased by 8.5 and 9.4 minutes, respectively.31 Policies to address neighborhood disorder are needed to impact sleep quality and overall health.
State or regional level factors also appear to influence sleep and health disparities. In a study that included data from 36 states,32 it was found that those in southern states are more likely to report difficulty sleeping even after controlling for age, sex, ethnoracial group, education, income, employment, general health, health care access, and depression. States with highest rates of sleep disturbance included West Virginia, Oklahoma, Missouri, Arkansas, Mississippi, and Alabama.32 The authors state that these findings suggest “that there is an independent effect of ‘place’ [on sleep disturbance] that is not completely explained by demographics, socioeconomics, health, regional differences in sunlight and weather patterns, and other factors,” and it is possible that other factors that were not assessed, such as “regional differences in public policy, social norms, belief and attitudes, or habitual health-related behaviors,” may contribute to the results.32
Another personal as well as neighborhood and regional environmental factor that affect sleep health is nighttime light exposure; an urban area has more nighttime light pollution compared with a rural area. Light is a powerful modulator of our circadian rhythm, which is a critical process that regulates sleep. In simplified terms, darkness tells our brain that it is time to sleep, and light tells our brain that it is time to be awake. Exposure to light from electronics, particularly in the blue light spectrum, suppresses melatonin,33,34 and adolescents may be particularly vulnerable. Furthermore, blocking nocturnal blue light may improve sleep quality.35 In additional to exposure to light from electronic personal devices, approximately 83% of individuals in the world and 99% of individuals in the United States and Europe are exposed to nighttime “light pollution.”36 Living in areas with higher outdoor nighttime light in the United States has been significantly associated with more sleep–wake variability, shorter sleep duration, increased daytime sleepiness, and greater dissatisfaction with sleep quantity and quality.37 A study by James et al38 found that women exposed to high amount of light at night are at a higher risk of break cancer, particularly for those who were premenopausal at diagnosis and had a history of smoking. Light directly affects circadian rhythm through the circadian/biological system, and light can also indirectly affect circadian rhythm by enabling activities that contribute to circadian rhythm disruption such as night or shift work or inconsistent sleep and wake times.39 Approximately 75% of workers in industrialized countries work outside 8:00 am to 5:00 pm.40 The circadian and sleep disruption experienced by shift workers increases incidence of cancers, CVD, diabetes, obesity, and mood disorders.40 Although the invention of electricity has obvious benefits, exposure to light also disrupts sleep and can result in adverse health outcomes.
Social norms are another social determinant of health that affect sleep and sleep health and health in general. Up 10 to 15 years ago, the social norm for prioritization of sleep could be summed up with the adage “you snooze, you lose.” In April 2017, Reed Hastings, the CEO of Netflix, said sleep was their biggest competition.41 Netflix would prefer you watch more television (and their advertisers) than sleep. In the past several years, the social norms around sleep have started to shift. Some evidence that the social norms are shifting or perhaps contributing to the shift is the increase in research being done on the effect of sleep on health and the risk for developing chronic conditions, including CVD.
Our physical therapy profession's norms are also shifting regarding sleep. In the past few years, there has been an increased interest in our profession to incorporate the assessment of sleep issues and promotion of sleep health into our clinical care and practice.42–46 Our profession is likely at the beginning of that shift. A survey published in 2015 of practicing physical therapists (PTs) reported that 95% of respondents agreed that addressing sleep issues may affect PT outcomes, but the majority (75%) did not receive education about sleep during entry-level PT education. Our profession's social norms regarding sleep health will continue to shift while entry-level Doctor of Physical Therapy (DPT) programs integrate information about prevention and health promotion (including sleep health) into entry-level curricula and while more and more practicing clinicians learn through professional organizations, continuing education opportunities, or self-study about the importance of sleep for proper functioning of the body, recovery, and optimal health and how to effectively incorporate screening of sleep issues and promotion of sleep health into practice. It is anticipated that this shift in culture will have a positive influence on clients' health and well-being.
Resources tailored for physical therapy practice are available to guide physical therapists to screen clients for sleep issues and to educate their clients on sleep health promotion techniques.43,45 Those sleep health promotion techniques should be tailored to the individual considering each level of the SEM (Fig. 1) and the individual's motivation to change their sleep behavior. Although there is no screening tool that we are aware of that specifically assesses SDOH that have been shown to directly or indirectly affect sleep health, the CLEAR toolkit is a resource to screen for key domains related to SDOH and is available for free in several languages.47 The CLEAR toolkit provides concrete steps to ask clients about social and environmental factors that affect health, refer the patient to community resources, and to advocate for healthier communicates.47 The CLEAR toolkit includes the example question “Do you and your family have a safe and clean place to sleep?” to screen for the domain of “housing.” Other possible questions to screen factors (including SDOH) across the SEM that may be affecting sleep health are included in Table 1. It is recommended to have a list of local community resources readily available to refer clients for services,48 including a list of referrals for further assessment and treatment of sleep disturbances. Board-certified sleep medicine physician can be found in or near your community by searching by zip code on the sleepeducation.org Web site.49
In conclusion, deviations from the recommended 7 to 8 hours of sleep/night may be a nonspecific marker for increased CVD risk.3 Public health campaigns are needed to continue to advance sleep health promotion effort, and evidence-based sleep recommendations should be included in health guidelines.1,3 Also, clinicians, including physical therapists, should screen for sleep issues and promote sleep health with all clients. In addition to general health screening, SDOH need to be screened and SDOH-informed interventions are needed. In summary: “Clinicians should counsel all their patients regarding sleep health. They need to take the patients' structural, social, and environmental context into consideration, as occupational and/or home demands, environmental disturbances, and other social factors may all present challenges to achieving sleep health.”9 Because sleep health affects overall health, including risk of CVD, SDOH are a critical consideration to patient-centered care.
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