Type 2 Diabetes:

• Sleep disturbances are an under-recognized factor that play a role in type 2 diabetes, including an increased risk of developing diabetes. A meta-analysis in 2010 found that both quantity and quality of sleep consistently and significantly predicted one’s risk of developing type 2 diabetes. 
• Possible etiologies include changes in energy homeostasis as well as insulin resistance and impaired pancreatic beta cell function. Data suggest that some melatonin receptor polymophisms and alterations in melatonin regulation may be associated with impaired insulin secretion and resistance
• Cortisol itself has a circadian rhythm, and alterations in cortisol may represent an additional mechanism by which sleep impacts risk of type 2 diabetes

Sleep duration and quality may serve as predictors of hemoglobin A1c (HbA1c), an important marker of glycemic control. In one study, a perceived sleep debt of 3 hours per night was associated with a significant increase in HbA1c. Another study demonstrated that patients with type 2 diabetes that had poor sleep quality and less-efficient sleep had worse glycemic control. 

• Interestingly, a dose-response meta-analysis of prospective studies demonstrates that too much of a good thing may also not be good when it comes to sleep: the relationship between sleep duration and risk of type 2 diabetes is U-shaped with 7-8 hours per day being the optimal range.

Cardiovascular disease:

• The American Heart Association added getting healthy sleep as part of its Life’s Essential 8™ as an important part of “lifelong good health.” The other factors include: (1) Eat better, (2) Be more active, (3) Quit Tobacco, (4) Manage weight, (5) Control cholesterol, (6) Manage blood sugar, and (7) Manage blood pressure. 
• New research presented at the American College of Cardiology (ACC) Annual Scientific Session in 2023 suggests that “young people who have more beneficial sleep habits are incrementally less likely to die early” and that “about 8% of deaths from any cause could be attributed to poor sleep patterns.”
• Short sleep has been associated with a higher burden of subclinical noncoronary atherosclerosis in healthy middle-aged adults. One potential mechanism may be inflammation. In addition, poor quality and quantity of sleep may have arrhythmogenic consequences. A 2018 meta-analysis capturing self-reported sleep in over 14 million individuals (over 10 observational studies) found that self-reported insomnia and frequent awakenings may be risk factors for atrial fibrillation

• Sleep apnea is one sleep disorder that may be an important predictor of cardiovascular disease. Evidence suggests that patients with obstructive sleep apnea (OSA) have an increased incidence of hypertension, and that sleep apnea is a potential risk factor for development of hypertension. OSA is associated with coronary heart disease, heart failure, and cardiac arrhythmias, as well as pulmonary hypertension (particularly in patients having pre-existing pulmonary disease). OSA may also be implicated in stroke and transient ischemic attacks (TIAs). Although researchers have not yet identified the causative agent that links OSA with cardiovascular disease, some proinflammatory mechanisms have been identified:
  • OSA is associated with increased sympathetic activity
  • OSA patients often have autonomic abnormalities: increased resting heart rate, decreased R-R interval variability, and increased blood pressure variability
  • OSA as well as atherosclerosis both may present with endothelial dysfunction, increased C-reactive protein, interleukin 6, fibrinogen, plasminogen activator inhibitor, and reduced fibrinolytic activity
  • OSA is associated with enhanced platelet activity and aggregation
  • New research presented at the American College of Cardiology (ACC) Annual Scientific Session suggests that “young people who have more beneficial sleep habits are incrementally less likely to die early” and that “about 8% of deaths from any cause could be attributed to poor sleep patterns.”

Obesity:

• Data suggest a potential causal relationship between poor sleep and greater rates of weight gain; however, a reverse causation may also exists, as obesity leads to many comorbidities (eg, obstructive sleep apnea), that may disrupt sleep duration and compromise sleep quality. The relationship between sleep duration and obesity is complex; some argue that more evidence is needed before we can consider sleep duration a modifiable risk factor for obesity
• The largest and longest study on adult sleep and weight is the Nurses’ Health Study, which followed approximately 68,000 middle-age American women for up to 16 years, and found that those who slept five hours or less were 15% more likely to develop obesity over the course of the study. Another Nurses’ Health Study demonstrated that women’s risk of developing diabetes and obesity increased the longer they worked rotating night shifts
• Smaller studies of experimentally sleep restricted adults reveal one possible mechanism linking short sleep duration to weight gain and diabetes: through the effects on appetite as modulated by the satiety / hunger hormones, leptin and ghrelin.
• Although studies have demonstrated that too much sleep may be linked to obesity, too little sleep may also increase one’s risk: The totality of evidence suggests a U-shaped association between sleep duration and obesity in adults. In other words, both short and long sleep duration may be associated with obesity. “This could be related to the complex mechanisms…but could also reflect the potential role of sleep duration as a marker for development of unhealthy lifestyles or for confounding as a result for existing unrecognised morbidity rather than being causal for obesity” 
• In fact, many conditions have cyclical relationships with disturbed sleep where lack of sleep compounds the symptoms of the disease, which further exacerbates the sleep disturbance: for eg, osteoarthritis “increases the risk of sleep disturbance, and both pain and sleep problems may trigger functional disability and depression.”
• Obstructive sleep apnea (OSA) is seven times more common in individuals with obesity (body mass index [BMI]  > or = 30); and as the prevalence of obesity increases, the OSA prevalence also increases

Depression:

• The relationship between depression and sleep disturbances is likely bidirectional

• The CDC tells us that the interrelatedness between sleep and depression is complex: although we have long understood that sleep disturbance is a symptom of depression, research also demonstrates that depressive symptoms may be resolved once patients with sleep apnea are successfully treated with continuous positive airway pressure (CPAP).
• According to the SleepFoundation.org, sleep issues commonly associated with depression include:
  • Insomnia
  • Hypersomnia
  • Obstructive sleep apnea
• Serotonin is a critical factor linking dysregulation of the circadian system and mood; thus some theorize that stress-induced alterations of the 5-HT system may disrupt circadian processes and increase one’s susceptibility to mood changes and depression

Chronic pain:

• Approximately 67-88% of chronic pain disorders are accompanied by sleep complaints; and at least 50% of patients with insomnia suffer from chronic pain. Insomnia is the most commonly diagnosed sleep disorder, and importantly, shares many comorbidities with chronic pain including obesity, type 2 diabetes, and depression. In general, researchers have found that patients with chronic pain and sleep disturbances experienced more severe pain and worse outcomes
• According to a 2020 review, patients who experience chronic pain paired with sleep disturbances may have “greater symptom severity, longer duration of symptoms, more disability and additional comorbidities.”
• Evidence demonstrates that there is a bidirectional relationship between sleep and pain: increased pain potentially influences quality and quantity of sleep; yet sleep also may influence our experience of pain. One hypothesis is that sleep disturbances impinge upon repair processes that may be important mediators of chronic pain development through dopamine and endogenous opioid signaling pathways.

Race / Ethnicity and Sleep:

Data show that there is a higher prevalence and severity of sleep disorders among patients of color and underrepresented populations. 

• Health survey studies tell us that higher rates of short sleep and on the other spectrum, higher rates of long sleep (greater than 9 hours) may be experienced by black people more often than other groups. 
• Both short and long sleep have been associated with higher overall mortality rates. Hispanic and Latino people also report an increased prevalence of short and long sleep, as well as low-quality sleep. 
• Differences in sleep among racial and ethnic groups are difficult to ascertain because these disparities have not been replicated in controlled sleep environments. According to SleepFoundation.org, this “points to a strong influence from social, economic, and cultural factors,” including:
  • Stress leading to an hyperarousable state, which may be a major contributor to insomnia
  • Shift work, which may disrupt the natural circadian rhythm that depends on exposure to light and melatonin production in dark environments
  • Occupational hazards, including exposures to allergens and irritants that may increase one’s risk of susceptibility to sleep apnea
  • Fear, anger and sadness stemming from racial discrimination may contribute to one’s overall stress level, thus spilling over into one’s ability to achieve efficient sleep
  • Financial stress due to unemployment and poverty, increasing one’s overall daily stress and ability to sleep
  • Neighborhood environment impacts sleep, as communities of color may experience higher levels of noise pollution, air pollution, allergens, and other exposures that can aggravate sleep disturbances and conditions such as sleep apnea
  • Unequal access to medical care among people of color means that sleep conditions like sleep apnea are less likely to be diagnosed and properly treated

Impact of Socioeconomic Status (SES) on Sleep:

1. Many researchers have written about sleep and its connection with the social determinants of health

• Both non-white and socioeconomically disadvantaged populations have worse outcomes across a wide range of health conditions, from HIV/AIDS, tuberculosis and other infectious, to asthma and other chronic pulmonary diseases, to cardiometabolic diseases
• Importantly, racial and ethnic disparities “persist even after stratification by education or household income”
• Minority racial and ethnic groups in the United States as well as individuals from low-income households experience a higher burden of sleep-related chronic illness
• A review by Grandner et al (2016) tells us that “disparities in sleep represent a pathway by which larger disparities in health emerge”
• Grander et al postulate that sleep may not only represent a modifiable risk factor for cardiometabolic disease in general, but may be “an important moderator in the relationship among minority status, socioeconomic disadvantage, and health.”
• “Clinicians should develop practices which recognize that racial/ ethnic minorities are more likely to present with high-risk sleep characteristics (including short sleep duration and sleep disorders), even if they do not specifically endorse complaints, without making biological assumptions about patients based on their race. Clinicians should counsel all their patients regarding healthy sleep. 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 healthy sleep.”

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4631795/

https://pubmed.ncbi.nlm.nih.gov/36115351/

https://journals.lww.com/cptj/Fulltext/2020/01000/The_Link_Between_Social_Determinants_of_Health,.3.aspx

https://www.thelancet.com/journals/laneur/article/PIIS1474-4422(22)00347-7/fulltext