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Many prior studies have noted the link between disordered sleeping and dementia as well. Getty Images
  • Researchers say getting more than 9 hours of sleep a night could indicate a higher risk of dementia.
  • Researchers studied more than 5,000 Latino adults and concluded that too much sleep was linked to a decrease in memory and episodic learning.
  • They haven’t determined if too much sleep leads to dementia, or if the disease itself brings on the extra sleep.

Could regularly “sleeping in” be a harbinger of cognitive decline, including Alzheimer’s disease and other forms of dementia?

A new study from the University of Miami Miller School of Medicine in Florida suggests it might.

Sleeping more than 9 hours per night was linked to a decrease in memory and episodic learning, both risk factors of dementia.

Researchers looked at a group of 5,247 Latino adults between 45 and 75 years old, a subset of data from the nationwide Hispanic Community Health Study/Study of Latinos. This group was observed both at the start of the trial and then 7 years later.

The results were clear to researchers.

“Insomnia and prolonged sleep duration appear to be linked to a decline in neurocognitive functioning that can precede the onset of Alzheimer’s disease,” Dr. Alberto R. Ramos, MSPH, research director at the University of Miami Sleep Disorders Program and a lead study author, said in a press statement.

The focus on a Latino population is particularly notable, says Rebecca Edelmayer, PhD, director of scientific engagement at the Alzheimer’s Association.

“Research related to sleep and cognitive decline has been happening for some time, but this is the first time the relationship between sleep duration and cognition has been studied in a U.S. Hispanic/Latino population,” Edelmayer told Healthline. “These findings are particularly important, because Hispanics are 1.5 times more likely to develop Alzheimer’s compared to whites.”

Much research has been done on the links between poor sleep — both too much and too little — and its link to Alzheimer’s disease and other dementias.

What’s less clear, and this research likewise doesn’t address, is whether poor sleep is the cause of cognitive decline or an early bellwether for it.

“The relationship between sleep and dementia is complicated,” Dr. Verna Porter, a neurologist and director of programs for dementia, Alzheimer’s disease, and neurocognitive disorders at Providence Saint John’s Health Center in California, told Healthline.

“Different types of dementia are associated with different sleep problems. It remains unclear whether poor sleep causes or exacerbates dementia, or if dementia leads to poor sleep quality. Some researchers believe that both of these theories could be true, and further research will be needed to better elucidate these relationships,” she said.

This study was also self-reported, not a full sleep study, and only looked at a Latino population, Porter notes, meaning we shouldn’t generalize to the total population at-large.

“Don’t sound the alarms,” Shaheen Lakhan, MD, PhD, MEd, MS, FAAN, vice president of research and development at The Learning Corp, the maker of cognitive therapy app Constant Therapy, told Healthline.

“Sleep patterns are highly individualized, and there were no objective measures recorded, as in a formal sleep study. In fact, sleep quality — that is, how restorative the sleep is and objective staging of sleep — may be more of an indicator than anything else. For some people, it just takes more sleep to achieve restoration of brain health,” he said.

That said, many prior studies have noted the link between disordered sleeping and dementia.

Beyond that, “there are other known warning signs that individuals should be on the lookout for, including difficulty completing familiar tasks, confusion and disorientation, and problems with speaking or writing,” Edelmayer said.

She points to the Alzheimer’s Association’s 10 Early Signs and Symptoms of Alzheimer’s page as a guide.

But while more research might be required to determine strict cause and effect between sleeping too long and dementia risk, people can make changes to their lifestyle today that can help mitigate their risks for cognitive decline in their later years.

“Guarding your downtime and making sure you are not only getting a normal amount of sleep but good quality sleep is a good long-term strategy to protect your brain health,” said Dr. Jagdeep Bijwadia, a board-certified doctor of sleep medicine and chief medical officer of sleep health at technology startup Beddr.

“Studies have shown that engaging your brain by learning new skills, keeping emotionally healthy with strong social networks, and sleeping well are helpful to brain health and may stave off cognitive decline,” Bijwadia told Healthline.

Beyond that, the latest research suggests that eating a low-fat, high-vegetable diet and getting regular exercise can also help mitigate the risk of developing Alzheimer’s disease, Edelmayer says.

“This is exciting research, because even though people can’t change some things — like their genes — most people do have some control over healthy habits,” she said.

However, if you find yourself regularly getting too much sleep (9 hours or more) or too little (less than 6), it might be time to go to the doctor.

The same goes if you’re sleeping a normal amount but don’t feel well rested.

“While sleep duration is highly variable, if a person regularly sleeps for 6 to 9 hours and still does not feel rested during the day, then seeking some medical advice may be a good idea,” Bijwadia said.