SECTION 4 - SLEEP AND HEALTH

Racial and Ethnic Disparities

Background

Racial and ethnic minorities have significant health disparities compared to the rest of the population. To achieve the objectives of the Healthy People 2010 initiative, there is a need for more consistent and reliable racial and ethnic data. Such data are needed to develop and implement effective prevention, intervention, treatment programs, policies, and services. For sleep disorders and for health status in general, efforts to eliminate disparities in health outcomes need to address not only social and environmental factors such as e ducation and access to health care, but also possible biological or genetic differences, including gene-environment interactions.

Many clinical conditions appear to contribute to racial and ethnic disparities in health outcomes. A few account for most of these disparities, including smoking-related diseases, hypertension, HIV, diabetes and trauma. The leading cause of death in African Americans and Hispanic Americans is heart disease. Sleep disorders (particularly Sleep-Disordered Breathing) may contribute to the increased prevalence and severity of heart disease, and may also contribute to these disparities through other mechanisms not yet clarified.

Progress In The Last 5 Years

- Since release of the original Sleep Disorders Research Plan in 1996, studies across ethnically diverse populations have identified significant differences in the prevalence of Sleep-Disordered Breathing (SDB) in African Americans and have suggested distinct pathophysiological mechanisms. Among young African Americans, the likelihood of having SDB is twice that in young Caucasians. Frequent snoring is more common among African American and Hispanic women and Hispanic men compared to non-Hispanic Caucasians, independent of other factors including obesity.

- SDB appears to be in part genetic, with increased prevalence not only in African Americans but also Asians and Hispanics compared to Caucasians. African Americans appear to have a different maxillo-mandibular structure than Caucasians, which may contribute to increased risk for SDB. African Americans with SDB develop symptoms at a younger age than Caucasians but appear less likely to be diagnosed and treated in a timely manner. This delay may at least in part be due to reduced access to care. Additional studies are also needed to explore the extent to which ethnic disparities in other diseases such as stroke and diabetes are related to a sleep problem such as SDB.

- The adverse impact of low socioeconomic status (SES) on health status may in part be mediated by decrements in sleep duration and quality. Low SES is frequently associated with diminished opportunity for sufficient sleep or environmental conditions compromising sleep quality. Hispanic children have less Stage 3 and 4 sleep and more Stage 2 sleep than their Caucasian counterparts, suggesting that there may also be racial/ethnic differences in sleep quality.

- Sleep loss has been shown to be associated with decreased glucose tolerance, elevated evening cortisol levels, and increased sympathetic activity. Sleep loss may thus contribute to increased risk for chronic conditions such as obesity, diabetes, and hypertension, all of which have increased prevalence in under-served, under-represented minorities. Racial and ethnic disparities related to obesity may also contribute to disparities in health outcomes related to SDB. Obesity is more common in African Americans and Mexican-Americans than in Caucasians.

- African Americans are at increased risk for cardiovascular disease, diabetes, infections, certain cancers and alcoholism. Recent studies suggest that alcoholics of African American descent may have more profound sleep abnormalities and abnormal immune function than Caucasian alcoholics and healthy individuals. Disordered sleep and sleep loss may disrupt the maintenance of internal physiological mechanisms. Therefore, investigating the interrelationships between alcoholism, sleep loss and ethnicity and irregularities in hormonal, autonomic nervous, and immune systems may yield new insights regarding mechanisms for the increased mortality rate among African American alcoholics.

- Blood pressure normally drops (dips) by about 10% during the night. African Americans, however, tend to be "nondippers" compared to Caucasians, independent of weight, gender and SDB. Studies in elderly African Americans and Caucasians suggest that for many older African Americans with hypertension, blood pressure does not fall the expected amount at night, and that this non-dipping is associated with more severe SDB. Non-dippers with high systolic blood pressure (SBP) during the day or high SBP or diastolic blood pressure (DBP) during the night were more likely to have more severe SDB. African Americans who are non-dippers may thus benefit from screening for SDB.

- Studies have also identified an increased prevalence of SDB in African American children compared to Caucasian children. African American children are also 50% less likely to have had their tonsils and adenoids removed (T&A) and more likely to have residual disease if a T&A has been performed. In children with sickle cell disease, there is not only a higher risk of SDB, but also higher prevalence and associated morbidity due to vaso-occlusive crises.

- Racial and ethnic disparities also appear to exist in the prevalence of other sleep disorders. Non-Caucasian adults report an insomnia rate of 12.9% compared to only 6.6% for Caucasians. Genetic studies have shown a higher degree of genetic polymorphisms and lower linkage disequilibrium in some populations, especially African Americans. Narcolepsy studies conducted in African Americans have resulted in identification of specific HLA alleles that are involved in mediating HLA class II susceptibility to narcolepsy (e.g., HLA-DQB1*0602).

- The relationship between health-related quality of life (HRQOL) and SDB has been examined in elderly African Americans screened for snoring and daytime sleepiness who completed a sleep recording, a comprehensive sleep questionnaire (Quality of Well-Being Scale, QWB), and the Medical Outcomes Study Core Measures of HRQOL. Those with moderate-severe SDB had significantly lower Physical Component outcomes summary scores than those with no SDB. Mild but not more severe SDB is independently related both to general physical functioning and general mental health functioning. The QWB scores of this SDB sample were similar to those found in patients with depression and chronic obstructive pulmonary disease, suggesting that sleep disturbances may impact daily living and health as much as other medical conditions.

- African Americans appear to have fewer chronic sleep complaints than Caucasians. The largest differences are in waking during the night, with African Americans having a prevalence of wakefulness during sleep of only about 60% that in Caucasians. The percent prevalence of insomnia for African Americans is also lower (19.8% vs. 23.6%). African American women have a higher incidence of insomnia than African American men, perhaps related in part to higher risk for chronic persisting symptoms. Caucasian males and females do not differ in incidence. Depressed mood is associated with insomnia in both racial groups. Continued presence of fair or poor health and physical mobility difficulties are associated with incident insomnia in Caucasians, but not among African Americans. The latter, however, show an association between incident insomnia and incident development of perceived fair or poor health. African Americans 75 years of age or greater are less likely than Caucasian or Hispanic Americans to attribute sleep problems, as well as heart disease and arthritis, to being part of the normal aging process (about 32% versus 46% and 43%, respectively).

- Interviews and polysomnography (PSG) have been conducted on Hmong people to collect data on sleep disorders and especially SDB in this ethnic group at high risk for Sudden Unexpected Nocturnal Death Syndrome. Hmong subjects appear to have a high prevalence of SDB.

Research Recommendations

- Conduct studies to identify the neurophysiological, neuroanatomical, genetic and gene-environmental interactions contributing to racial and ethnic disparities in prevalence and severity of individual sleep disorders.

- Develop strategies to reach under-represented minorities in public health education programs designed to maintain health and prevent development and progression of sleep-related conditions.

- Determine the extent to which higher prevalence of SDB and lower rates of diagnosis and treatment contribute to the higher prevalence of learning problems and academic underachievement in African American children.

- Determine the best public health approaches among underserved, under-represented populations for increasing access to and knowledge of Sleep Medicine resources.

- Determine the bi-directional link between parameters of sleep, sympathetic nervous system activity, and cellular immunity in African Americans with alcohol dependence.

- Determine the extent to which racial and ethnic disparities in health outcomes related to sleep disorders may contribute to differential responses to treatment or to differences in adherence to treatment recommendations.

- Determine whether ethnic differences in alcohol-induced sleep disturbances contribute to the sympathetic nervous system and immunological effects of alcohol.

- Develop effective strategies to include racial and ethnic minorities in overall efforts to recruit increased numbers of biomedical investigators to sleep-related research and in sleep-related curriculum development for health care professionals.