Article In Brief
In a large study of Hispanics/Latinos in the US, researchers found that long sleep duration was associated with worse neurocognitive performance and it could be predictive of neurocognitive decline.
In one of the largest and most comprehensive studies of cognitive decline in underserved communities, researchers found an association between memory issues and sleep in Hispanic/Latinos from communities across the country.
The study, reported in the October 9 online edition of Alzheimer's & Dementia, found that, over a seven-year observational period, sleep problems among Hispanics were associated with the risk for problems in memory, phonemic fluency, and mental status.
“Our findings identified important sleep correlates of neurocognitive decline that can precede the onset of dementia, providing a target for early intervention to prevent or ameliorate the onset of disease, more so in Latinos, a high-risk group,” said Alberto Rafael Ramos, MD, associate professor of clinical neurology at the University of Miami Miller School of Medicine, and the lead author of the study.
“We think that long sleep might be a surrogate for poor sleep quality,” he said.
“We [also] think that people may spend longer times in bed because there is always a sleep need as they may have lower amounts of slow-wave sleep and increased fragmented sleep. This is just a hypothesis that we will be testing. For now, we just don't know why a longer sleep duration drives cognitive decline.”
He said the strength of the study is that they researched many aspects of the sleep cycle and assessed demographic, behavioral and vascular risk factors, along with sleep-disordered breathing, daytime sleepiness, and insomnia. The risk for Alzheimer's disease (AD) in Latinos is 1.5 to four times higher compared to non-Hispanic whites, he said, and researchers are trying to figure out why.
Study Design, Findings
Dr. Ramos has spent his career studying cardiovascular disease and sleep problems, and health disparities in Latino communities. He and his colleagues began studying cardiovascular risk factors in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL), which followed 16,145 people across four large cities: Chicago; Miami; Bronx, New York; and San Diego. In this study, they identified a high number of sleep problems that were tied to cardiovascular disease, stress, and the cultural climate of minority groups in the United States.
In the HCHS/SOL study, they also found that self-reported breathing difficulties during sleep were associated with memory, language, and executive functioning problems. People who reported too little sleep (under six hours) and too much sleep (more than nine hours) had neurocognitive problems compared to those who had more normal sleep duration (around seven to eight hours).
These findings led to the present analysis—the Study of Latinos-Investigation of Neurocognitive Aging (SOL-INCA). The researchers wanted to see whether the sleep patterns predicted neurocognitive decline in middle-aged and older Latinos.
They measured sleep-disordered breathing, daytime sleepiness, insomnia, and self-reported sleep duration as potential risk factors of neurocognitive change over a seven-year study period. They thought that they would find a similar U-curve in the risk for cognitive decline—that people with short- and long-sleep patterns would fare worse than those who had more normal sleep durations, between six to nine hours a night.
For the new study, they pulled data on the middle-aged and older population from the HCHS/SOL cohort. These were Latinos whose families had immigrated from Central America, Cuba, the Dominican Republic, Mexico, Puerto Rico, and South America. They had collected baseline information on socioeconomic status, medical history, sleep problems, and lifestyle habits (smoking and exercise). They collected body measurements, drew blood, and conducted oral glucose tolerance tests. They also had neurocognitive test measures on 9,623 middle aged and older adults.
The SOL-INCA study began as the HCHS/SOL study was entering its second testing period, from 2015 to 2018. They enrolled 5,247 participants and repeated the neurocognitive tests that were done at baseline, and administered the Trail Making Tests, parts A and B. The study participants also filled out a sleep habits questionnaire that includes information of weekday and weekend bedtime and wake-time habits, napping, sleep-disordered breathing symptoms, snoring and apnea. They had information on who was taking sleep medication and how much they were taking. Participants also filled out depression assessments.
The researchers were surprised to find that only long-sleep duration was associated with participants' seven-year cognitive decline on measures of episodic learning and memory.
“We observed that worse sleep in the form of prolonged periods of sleep (greater than nine hours) and insomnia symptoms led to neurocognitive decline in memory, executive function, and processing speed,” said Dr. Ramos. “These measures can precede the development of mild cognitive impairment and Alzheimer's.”
“We also obtained measures of sleep apnea, a known confounder of impaired cognition, in addition to simultaneous information on daytime sleepiness and insomnia within a single cohort,” Dr. Ramos said. “No previous studies have used data from a representative sample of US Hispanic/Latinos.”
He said that they were “surprised that measures of sleep apnea were not significant in this study. We think that other risk factors for neurocognitive decline may be more prominent in Hispanics (such as hypertension and diabetes) and may obscure any associations between cognition and sleep apnea,” he said. “Or we need to obtain better sleep measures in follow-up studies.”
He added that the self-reported long sleep duration may be a marker of poor sleep efficiency, fragmentation, or circadian misalignment, which may promote neurocognitive decline and impairment. It could also be that the longer sleep duration could be caused by undocumented pathological changes observed in mild cognitive impairment and early AD.
Dr. Ramos noted that there were health risk variations among those from different Latino backgrounds; for example, individuals of Caribbean descent seemed to have more dementia/MCI and such risk factors as hypertension. This study was not designed to study differences between various Latino populations, however.
“Future studies should look into similarities and differences in the relationship between sleep and cognitive decline in Latinos living within and outside the States.”
—DR. YAKEEL T. QUIROZ
The researchers will continue to study this cohort. “We want to quantify the role of sleep disorders, sleep quality, and cerebrovascular disease as a pathway to neurocognitive decline. And we want to evaluate chronotype (circadian rhythms-internal clock) and genetic studies that can clarify causal associations with neurocognitive decline,” Dr. Ramos said.
“Sleep is one of several risk factors for Alzheimer's and other dementias, as well as for cardiovascular disease and depression,” said Jaime Perales Puchalt, PhD, a postdoctoral fellow at the University of Kansas Alzheimer's Disease Center. “The importance of this study is its large Latino sample size. The way they recruited Latinos is more representative of the Latino community than other studies. They included a diverse group of Latinos in terms of ancestry (Mexican, Cuban) and nativity (US or foreign born). They also used validated measures in both English and Spanish.”
“There are very few studies that focus on minority groups,” added Nicte I. Mejia MD, MPH, assistant professor of neurology at Harvard Medical School and director of neurology community health diversity and inclusion at Massachusetts General Hospital. “As a neurologist, I think a lot about sleep. This study resonates with the idea that sleep matters for brain health,” Dr. Mejia said.
She said that “the study sparks my curiosity: Were people sleeping longer because they were depressed or socially isolated? Were people drinking alcohol to help them sleep? I was also left thinking about socioeconomic factors that could affect sleep, including the types of jobs that Latinos may have had in this study, particularly if they had to work the night shift or hold two or three jobs to make ends meet.”
“Clinicians need to proactively engage in culturally humble conversations about sleep with all patients, including Latinos,” she said, “keeping in mind that socioeconomic factors may influence people's experiences and outcomes.”
Yakeel T. Quiroz, PhD, assistant professor of psychiatry at Massachusetts General Hospital, agreed. “The socioeconomic climate in the US can lead to long workdays and nights, and unfortunately, one of the first things to go is sleep hygiene.”
Dr. Quiroz added that given the unique characteristics of the Latinos living in the US it will be hard to make generalizations of the findings to Latinos living in their countries of origin. “Future studies should look into similarities and differences in the relationship between sleep and cognitive decline in Latinos living within and outside the States,” she said.
Drs. Ramos, Puchalt, Mejia, and Quiroz had no competing interests.