We know a good night's sleep is essential for a healthy, fulfilling life. But how much sleep is "enough"? It turns out there's a Goldilocks answer: your sleep time must be just right—not too much, and not too little.

A new study led by researchers at the Washington University School of Medicine in St. Louis linked sleeping less than 5.5 hours a night and more than 7.5 hours to greater cognitive decline—including a higher risk for Alzheimer's disease.

The study, published in the journal Brain, monitored the sleep-wake activity of 100 participants over four to six nights and then monitored their cognitive function for 4.5 years. They underwent standardized cognitive testing, apolipoprotein E (AOPE) genotyping—a procedure that evaluates a genetic risk of Alzheimer's disease—and measurements of Alzheimer's biomarkers like amyloid protein plaques and tau protein tangles.

Sleep and brain health: it’s a u-shaped relationship

The researchers found a U-shaped relationship between sleep and cognitive decline for groups that slept less than 5.5 hours or more than 7.5 hours per night. The results held constant for measures of specific sleep phases, including rapid eye movement (REM) and non-REM sleep, age, sex, levels of Alzheimer's proteins, and the presence of APOE4, a gene variation associated with the neurodegenerative disease.

"Our study suggests that there is a middle range, or "sweet spot," for total sleep time where cognitive performance was stable over time," explained the authors.

These findings shed light on possible ways to fight back against cognitive decline and maintain a sharp mind as we age.

How much sleep do you need for cognitive function?

Sleep plays a vital role in learning and memory formation. To ensure you're getting the most out of your sleep time, the Center for Disease Control and Prevention recommends getting seven to eight hours of sleep.

You can maximize the cognitive benefits of sleep by nourishing your brain with nutrient-dense, antioxidant-rich foods and help protect memory and cognition.

Does lack of sleep increase your Alzheimer's risk?

There's a bi-directional relationship between sleep and Alzheimer's disease. While poor sleep is a symptom of Alzheimer's disease, a lack of sleep and sleep disorders like insomnia are associated with cognitive impairment and an increased risk for Alzheimer's.

But the detrimental effects of getting either too much or not enough sleep also affect our overall health, increasing the risk of several health concerns like cardiovascular disease, diabetes, even an increased risk of mortality.

How to improve the quality of your sleep?

Getting enough sleep is crucial to our overall well-being. If you're struggling to get the right amount of ZZZs for you, here are three tips to help you improve your sleeping habits and get more quality time in dreamland.

1. Hack your sleep disturbances with food

   —Some foods have sleep-promoting properties and can help you improve your quality of sleep.
• Try a handful of almonds before bed; they're an excellent source of magnesium and melatonin, two sleep-enhancing nutrients.
• Eat a small portion of turkey a few hours before bed—it contains high levels of the amino acid tryptophan, which helps increase melatonin production.
• End your nights with a nice cup of chamomile tea. It's packed with antioxidant-rich flavones that promote sleepiness and improve overall sleep quality.
• If you're craving something sweet before bed, have some kiwi. It's rich in serotonin and antioxidants, both of which can help you get more restful sleep.

2. Move more, sleep better

   —Having a regular exercise routine is terrific for whole-body health. In particular, it does wonders for your sleep quality. Engaging in moderate-to-vigorous exercise during the day can help you fall asleep faster. Plus, exercise also helps manage a healthy weight, making you less likely to experience sleep apnea. Lock in your sweat session at least a few hours before bedtime, so your body has time to unwind and relax.

3. Better ZZZs with nutritional support

   —Build sustainable daily habits that support a sleep-friendly lifestyle, and you can complement your smart choices with nutrients like ashwagandha, melatonin and valerian root—well-known for supporting healthy sleeping patterns.

References

• Acosta, Teresa María. "Sleep, Memory, and Learning." Medicina (B Aires). 2019. https://pubmed.ncbi.nlm.nih.gov/31603840/
• Ansel, Karen. "9 Foods to Help You Sleep." EatingWell. October 2021. https://www.eatingwell.com/article/32617/9-foods-to-help-you-sleep/
• Irwin, R. Michael, Michael V. Vitiello. "Implications of Sleep Disturbances and Inflammation for Alzheimer's Disease Dementia." Lancet Neurol. March 2019. https://pubmed.ncbi.nlm.nih.gov/30661858/
• Lucey, P Brendan, et. al. "Sleep and Longitudinal Cognitive Performance in Preclinical and Early Symptomatic Alzheimer's Disease." Brain. September 2021. https://academic.oup.com/brain/article-abstract/144/9/2852/6401973?redirectedFrom=fulltext
• Pachecho, Danielle. "Exercise and Sleep." Sleep foundation. December 2021. https://www.sleepfoundation.org/physical-activity/exercise-and-sleep
• Sadeghmousavi, Shaghayegh, et. al. "The Effect of Insomnia on Development of Alzheimer's Disease." Journal of Neuroinflammation. 2020. https://jneuroinflammation.biomedcentral.com/articles/10.1186/s12974-020-01960-9
• Suni, Eric. "The Best Foods to Hellp You Sleep." December 2021. https://www.sleepfoundation.org/nutrition/food-and-drink-promote-good-nights-sleep
• Wang, Chanung, David M. Holtzman. "Bidirectional Relationship Between Sleep and Alzheimer's Disease: Role of Amyloid, Tau, and Other Factors." Neuropsychopharmacology. January 2020. https://pubmed.ncbi.nlm.nih.gov/31408876/
• "Hit the Sleep ‘Sweet Spot' to Keep Brain Sharp." Science Direct. October 2021. https://www.sciencedaily.com/releases/2021/10/211020135920.htm
• "Sleep and Sleep Disorders." Center for Disease Control and Prevention. https://www.cdc.gov/sleep/data_statistics.html
• Lin HH, Tsai PS, Fang SC, Liu JF. "Effect of kiwifruit consumption on sleep quality in adults with sleep problems." Asia Pac J Clin Nutr. 2011. https://pubmed.ncbi.nlm.nih.gov/21669584/

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The Life Extension Health News team delivers accurate information about vitamins, nutrition and aging. Our stories rely on multiple, authoritative sources and experts. We keep our content accurate and trustworthy, by submitting it to a medical reviewer.