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Summary: Yes, a recent study indicates that people with depression who sleep longer than average may be at risk of mild cognitive impairment and dementia.

Key Points:

  • People who regularly sleep longer than 9 hours per night are at increased risk of depressive symptoms
  • People with depression who sleep longer than 9 hours per night are at increased risk of cognitive problems
  • Long sleep was associated with lower scores on cognitive tests in people with and without depression
  • Treatment can mitigate the impact of excessive sleep on cognition among people with depression

Sleep Problems, Depression, and Cognition: New Research Reveals Connections

Some people with depression have problems sleeping, while other people with depression may sleep too much. Most of us likely think problems related to the interaction between sleep and depression revolve around getting too little sleep, and experiencing the negative effects of sleep deprivation. And most of us also understand the consequences of sleep deprivation: poor mental performance, trouble concentrating, anger, irritability, problems with memory, problems making decision, and problems handing stress.

But what most of us don’t know is that too much sleep can cause problems for people with depression, and the primary problem associated with too much sleep among people with depression may be surprising: cognitive impairment, cognitive decline, and among older patients, dementia.

To explore whether too much sleep can cause problems for people with depression, a group of researchers based in the U.S., Canada, and Australia designed a study called “Long Sleep Duration, Cognitive Performance, and the Moderating role of Depression: A cross-sectional Analysis in the Framingham Heart Study” and published the results in July 2025.

Here’s how they describe their study:

“We investigated whether depression modified the associations between sleep duration and cognitive performance.”

To explore these associations between sleep, depression, and cognitive performance, researchers examined records of 1853 patients between ages 27-85 participating in the Framingham Heart Study who agreed to engage in additional neuropsychological testing in the context of the larger research effort.

Let’s take a look at the details of the study.

Background on Research on Sleep Problems, Depression, and Cognition

The study team notes, at the outset, that connections between depression and sleep disorders is well-documented. Research on the connection between depression and sleep disorders shows:

  • 90% of people with depression reporting problems with sleep.
  • Sleep disorders are believed to precede depression rather than the contrary
  • Insomnia is the most common sleep disorder associated with depression

Depression-related brain changes are associated with cognitive impairment, including:

  • Heightened vulnerability to dementia
  • Effects persist after remission of depressive symptoms
  • Persistent effect may exacerbate negative cognitive impact of sleep problems on depression

Based on this information, the team hypothesized:

  1. Sleeping too much and sleeping too little would be associated poorer cognitive performance, compared to sleeping an average amount
  2. Compared to people without depressive symptoms, people with depression would display a stronger connection between sleep duration and cognition regardless of the use of antidepressant medication

To test these hypotheses, researchers divided study participants into four groups:

  1. No depressive symptoms/no antidepressants.
  2. Depressive symptoms/no antidepressants.
  3. Antidepressants use/no depressive symptoms.
  4. Depressive symptoms/antidepressant use.

Next, they administered a series of tests to measure levels of the following cognitive skills:

  • Attention
  • processing speed
  • Executive function
  • Visuospatial memory
  • Verbal learning and memory
  • Verbal reasoning

Research-verified metrics on cognitive performance included:

To assess presence and severity of depressive symptoms, researchers administered the 20-item Center for Epidemiologic Studies Depression (CES-D) Scale, a well-established, research-verified depression metrics.

Next, the team analyzed the cognitive performance results and cross-referenced them with sleep survey results to test their hypotheses. Before we share the results, let’s take a look at the basic facts on sleep, depression, and dementia.

Facts and Figures on Too Much Sleep, Depression, and Dementia

Here’s something we learned while researching this article:

“Each of us will spend about 27 years of his or her lifetime sleeping. This fact alone explains why neuroanatomists and neuro-physiologists have been studying sleep for over a century.”

That century of research has yielded the following body of information on the connection between sleep, health, and mental health.

Sleep Problems Not Insomnia: Prevalence

  • Experts use the phrase excessive sleepiness and hypersomnia interchangeably
  • People with hypersomnia fall into two categories:
    • Group A: people who sleep longer than most during their typical sleep hours: ~10% of adults
    • Group B: people who fall asleep when they should be awake: ~12% of adults

Clinica disorders defined by excessive sleep, such as narcolepsy, are uncommon. They’re characterized by a complex range of symptoms associated with unwanted sleep, including falling asleep suddenly anytime, cataplexy, and sleep paralysis.

These excess sleep disorders appear in about 0.04% of adults.

In this article, we focus on people who sleep too much, or people with hypersomnia. Causes of hypersomnia include:

  • Poor sleep hygiene
  • Shift work/work conditions
  • Psychotropic medication, i.e. antidepressants, anxiolytics, antipsychotics, mood stabilizers

Long term consequences associated with hypersomnia include:

  • Breathing-related sleep disorders, i.e. chronic snoring/sleep apnea
  • Psychiatric disorders, particularly depression
  • Various physical illnesses

Now let’s look at the latest data on the prevalence of depression and dementia among adults in the U.S. While dementia is most commonly associated with older people, it’s important to understand the interactive relationship between depression and cognition. When cognition is impaired in older age, it’s called dementia. Among younger people, it’s simply called cognitive impairment.

Prevalence of Depression and Dementia

Depression:

  • Major depressive episode (MDE), Adults 18+: 5%
    • 9 million people
  • Major depressive episode (MDE) with severe impairment 18+: 5.9%
    • 3 million people

Dementia:

  • Among adults 65+: 11%
  • Among adults 30-64: 0.11%
  • Risk of dementia for people who reach age 75: 50%

Dementia + Depression

Now that we understand the scope of the potential problem and the basic facts around the subject matter, let’s review the results of the study.

Results: Association of Long Sleep Duration on Cognition, or How Too Much Sleep Can Cause Problems for People With Depression

First, let’s look at the impact of longer sleep on depression, compared to an average amount of sleep. Note: throughout the study, researchers found no data connecting sleep short duration with cognition among people with depression. Therefore, all the following data will compare excess sleep, defined as 9 hours or more per night, with average sleep, defined as 7-8 hours per night.

Sleep Duration and Cognitive Performance

Model 1: Raw Scores

Model 2: Controlled for Demographic Variables

  • Longer sleep showed statistically significant associations with lower cognitive performance, compared to average sleep. Differences in cognitive overall cognition:
    • Model 1: -0.25
    • Model 2: -0.27
  • People who slept longer showed significantly lower performance on tests of complex sequential thinking:
    • Model 1: -0.09
    • Model 2: -0.07
  • Longer sleep showed statistically significant associations with lower ability to recall visual information:
    • Model 1: -1.80
    • Model 2: -1.76
  • People who slept longer showed significantly lower performance on tests that focus on pattern recall and pattern recognition:
    • Model 1: -1.50
    • Model 2: -2.16

That’s informative: longer sleep impacts cognitive performance independent of the presence of depressive symptoms. Next, we’ll share the data at the core of this article, and the core of the study we’re discussing: the impact of sleep time on cognition among people with depression.

Depression, Sleep, and Cognition: Short (Under 7 Hours) vs. Long Sleep Duration (Over 9 Hours) Compared to Average Sleep (7-8 Hours)

Here are the results related to the primary hypothesis of the study, which suggested sleep duration would mediate cognitive performance among people with depression. We’ll share the outcomes for the four groups we list above:

  1. No depressive symptoms + no antidepressants.
  2. No depressive symptoms + antidepressant use.
  3. Antidepressant use + no depressive symptoms.
  4. Antidepressant use + depressive symptoms

Short Sleep, Long Sleep, Depression, and Antidepressants: Impact of Sleep Time on Cognition

No depressive symptoms/no antidepressant use:

  • Overall cognition
    • Long sleep: lower scores
    • Short sleep: no difference
  • Trails B: no impact
  • Visual reproduction
    • Long sleep: lower scores
    • Short sleep: no difference
  • Similarities:
    • Long sleep: lower scores
    • Short sleep: no difference

No depressive symptoms + antidepressants use:

  • Overall cognition: no impact
  • Trails B: no impact
  • Visual reproduction: no impact
  • Similarities: no impact

Presence of depressive symptoms + no antidepressant use.

  • Overall cognition
    • Long sleep: lower scores
    • Short sleep: no difference
  • Trails B
    • Long sleep: lower scores
    • Short sleep: no difference
  • Visual reproduction
    • Long sleep: lower scores
    • Short sleep: no difference
  • Similarities: no impact

Antidepressant use + presence of depressive symptoms.

  • Overall cognition:
    • Long sleep: lower scores
    • Short sleep: no difference
  • Trails B: no impact
  • Visual reproduction
    • Long sleep: lower scores
    • Short sleep: no difference
  • Similarities: no impact

As we can see, these results indicate that long sleep, i.e. over 9 hours per night, is associated with lwer cognitive performances. Researchers estimate these differences have roughly the same impact on cognition as 6 ½ years of aging. In addition, outcomes were present across the entire age range of the study – people between 27 and 85 years of age – and among participants who neither took antidepressants nor reported depressive symptoms.

We’ll elaborate on these results below.

How Too Much Sleep Can Cause Problems for People With Depression

Here’s how study author Dr. Sudha Seshadri describes the outcome of this research effort in an interview with UT Health of San Antonio:

“Long but not short sleep duration was associated with poorer global cognition and specific cognitive abilities like memory, visuospatial skills and executive functions. These associations were stronger in people with depressive symptoms, regardless of antidepressant usage.”

Another researcher on the study adds:

“Sleep may be a modifiable risk for cognitive decline in people with depression.”

These outcomes are relevant to all people with depression, not only older people with concerns about age-related or Alzheimer’s disease-related cognitive decline. Since cognitive impairment can have a begave impact on recovery from depression and performance across life domains, the research team identifies areas of research that can leverage this new knowledge on sleep duration into improved treatment for people with depression:

  1. New studies are needed on novel sleep interventions to help reduce sleep time among people with depression.
  2. Retrospective meta-analyses are needed to determine which existing therapies are effective for improving sleep problems among people with depression.
  3. New clinical studies are needed on how providers can modify current therapeutic modalities to resolve sleep difficulties – particularly sleeping too much – among people with depression.

Problems associated with sleep most often revolve around problems caused by lack of sleep, which most of us know about: poor decision making, poor concentration, fatigue, anger, and irritability are all clear consequences of sleep deprivation, and they can all have a negative impact on life functioning and recovery from depression.

Now we know that the opposite – too much sleep, or hypersomnia – can also have a negative impact on life functioning and recovery from depression by increasing risk of cognitive impairment. Many of us are familiar with friends, family, or others who prefer to sleep it off when they face uncomfortable emotions. While getting a good sleep can help give us a fresh perspective and, at times, new insight upon waking, which may help people with depression, this new study tells us to monitor the sleep patterns of our patients with depression: sleeping too much may have a negative impact on current progress, and impair long-term recovery.

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