Cell body of a neuron long shot

Is this the purpose of sleep?

Despite massive scientific advancement in the last 50 years into our understanding of what sleep is and what it does for the body, the answer to the simple question, “what is the purpose of sleep,” has been elusive. Is there a single purpose for why we sleep? While we still don’t know an exact answer, we do have a clear understanding that the processes of sleep actively facilitate restoration of the mind and physical self for next-day functioning. And of course, all the findings in support of this idea, support what we know intuitively: proper sleep is necessary to function well and to feel good.

Last year, a major paper was published in the journal Science describing how, during sleep, the brain removes waste products. Lead author, Lulu Xie, said:

“The restorative function of sleep may be a consequence of the enhanced removal of potentially neurotoxic waste products that accumulate in the awake brain.”

Recently, one of the paper authors, Jeff, Iliff, gave a fascinating TED presentation describing just how the brain goes about removing waste and discusses possible implications for these observations. The video is only 11 mins long but it’s packed with interesting information, and dare I saw pretty, visuals. Enjoy!



  • Jon Rahoi

    “allusive” should be “elusive”, no?

  • danpardi

    Good catch, Jon.

  • SnoreRx

    Great article. It has great information on sleep’s restorative properties.

    • danpardi

      Thank you. Indeed, this was a fascinating discovery by this research group.

      • SnoreRx

        I meet a lot of people who don’t get the full night’s sleep that they need and the next day they can’t think clearly and describe slow thinking experiences. This link is great for sharing!

      • Arthur Gumz

        Hey Dan, I just read your guest post @ Chris Kresser website (about how to achieve optimal sleep) and would like to know from you how to get the best results from light exposure (is it best in the morning? midday? How many minutes our hours works best?)

        I do have one of those Light Therapy devices (http://tinyurl.com/k7k5p72) and leave it on for at least one hour near midday or in the afternoon. I`ve read from Paul Jaminet (Perfect Health Diet) that a morning walk first thing in the morning works wonders for the circadian rythm, should I try to make it a routine?

        Just one more question if you will – I have one of those transitions lenses (because of myopia). Does it diminish the benefits of getting light exposure on the eyes (and does normal lenses do the same, for that matter)? Thanks in advance.

        • danpardi

          Hi @arthurgumz:disqus, the majority of the benefits of daytime light exposure on circadian rhythm anchoring happen with about 5 hours of light exposure, but 80% of the effect happen from the first 30 minutes. Getting light exposure first thing in the day is not a bad idea. I think it’s valuable to get outside and go for a walk after you wake up in the morning. Having said that, you can get those 30 minutes really anytime after dawn and before dusk and you will experience adequate rhythm anchoring. Overcast skies dampen light intensity so aim to get a little more exposure on those days.

          Regarding your lenses, any lens that reduces transmittance of full spectrum and blue light will require you to get more daylight exposure across the day. How much? It’s hard to say, depends on the lenses and the day.

          • Arthur Gumz

            Thanks for the tips! Regarding those Light Therapy devices, for how long should I aim to leave them on? Does it substitute sun exposure on the eye?

          • danpardi

            Sure thing. Light therapy boxes are usually around 10K lux. The light intensity of outdoor light on a blue sky day is over 100K lux. Light therapy boxes do work. One protocol is to use it for 15 minutes a session, 2x per day.

          • Arthur Gumz

            Thanks again, Dan. I really appreciate it. 🙂

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