Much Ado About Sleep: the Importance of Getting Adequate Sleep

How was your sleep last night? Were you able to go to bed early and clock in a solid 7 to 9 hours of sleep, or were you tied up with work and had to postpone your bedtime till the draft was written and the email sent?

On average, we human beings spend 8 hours per day sleeping, which amounts to a total of one-third of our lifetime. That is, for a person who spends 75 years on earth, 25 years is spent sleeping. With such a significant amount of time spent in bed, one couldn’t help but wonder, what would happen if we just shift the bedtime later by an hour and a half, while keeping the wake-up time fixed? Surely it will not have much of an impact?

Well, turns out it will.

In a recent study published in Scientific Reports, Columbia postdoc Vikas Malik and colleagues found that for healthy females, after cutting sleep short by an hour and a half for a mere six weeks, cells that protect our blood vessels become negatively impacted. Evidence has shown that sleep restriction introduces a more pronounced risk for females than males, leading the researchers to focus solely on females for this study. With this reduction in sleep, the amount of harmful molecules (oxidants) starts to overpower that of the good molecules (antioxidants) in the cells. Since oxidants are harmful molecules which are responsible for producing the notorious “free radicals” and causing toxic effects in the body, and antioxidants good molecules responsible for detoxifying the body and repairing damages made by oxidants – this imbalance between the amount of oxidants and antioxidants will lead to impaired cell function and detrimental consequences in the form of cardiovascular diseases.

While the significance of sleep is well known, the mechanisms of how lack of sleep could impact human health has remained largely unclear. In fact, this study provides some of the first evidence demonstrating how mild chronic sleep deprivation could impact the health of our heart. In addition, contrary to previous studies that mainly examine sleep deprivation conditions in a compact time frame (e.g., acute sleep deprivation in flies for 10 days), the authors investigated how mild sleep restriction influences vascular cell health in females (i.e., pushing the bedtime 1.5 hours later than what the participants used to, while keeping the wake-up time fixed over the span of 6 weeks). Owing to a more “modern” work/life balance, the results from the authors’ experimental design carry higher relevance to our sleep patterns.

Specifically, the researchers found that after adequate sleep, the imbalance between oxidant (harmful) and antioxidant (good) molecules in the vascular cells can be cleared by a functional antioxidant response. This response is facilitated by a protein called serum response factor (SRF) – when sleep is adequate, the expression level of SRF increases to bring up the expression level of DCUN1D3, another protein which mediates antioxidant response of the cell. After sleep restriction, however, the antioxidant response cannot be turned on because the expression level of SRF is not adequate enough to activate a sequence of transcription of antioxidant genes, therefore hindering the restoration of balance between oxidant and antioxidant molecules in the cells (see illustration below).

Functional vs. impaired antioxidant response under adequate and inadequate sleep. Adequate sleep increases the expression level of SRF, which in turn increases the expression of DCUN1D3, freeing Nrf2 into the nucleus of the cell to activate the transcription of antioxidant genes, which then restores balance between oxidant and antioxidant molecules in the cells. Inadequate sleep, however, perturbs this process and interferes with the activation of antioxidant response. Figure is from the original publication.

These findings carry significant implications on how we should schedule our sleep. While deadlines will always be looming and stress will always be present, maybe we should still make the effort to defend our bedtime. After all, as Shakespeare puts it, sleep is the “balm of hurt minds, great nature’s second course, chief nourisher in life’s feast”. Perhaps, unlike Macbeth, we should all strive to sleep more.

Written by: Linbi Hong

Reviewed by: Vikas Malik, Trang Nguyen, Martina Proietti Onori, Giulia Mezzadri, and Patricia Cooney


The Importance of Consistent Sleep for Memory Retrieval at the Neural Level

Sleep helps us remember the details of past events more clearly. When we sleep, neural mechanisms facilitate the consolidation of memories formed during the waking day. Specifically, memories are temporarily stored in a brain structure called the hippocampus. During the consolidation process, memories are replayed and integrated into long-term storage centers in the neocortex of the brain. Poor sleep impairs sleep-based memory consolidation and memory retrieval. In other words, when our sleep is fragmented, our memory is less clear. 

One way to assess the clarity of a memory is to measure neural similarity, or the overlap between patterns of neural activity.  My colleagues and I presented participants with a series of word pairs to remember while we recorded their neural activity using electroencephalography. We used this task to measure neural activity when participants studied (i.e., encoded) and were tested on (i.e., retrieved) the word pairs. The overlap between their neural patterns for a given word pair at study and test is an index of neural similarity.

Interestingly, we found that sleep quality was associated with neural activity for word pairs that were paired differently. When people had more consistent sleep quality from night-to-night (measured with wrist-worn monitors), they had greater neural similarity when they correctly rejected word pairs that were paired differently. For example, if they saw the pair “wing – clock” during the study period and correctly identified “fork – clock” as a different pairing at test, they demonstrated higher neural similarity. 

There were several strengths of the study. We used an objective measure of sleep quality — wrist-worn monitors. We also measured sleep quality for seven nights, which allows for assessing night-to-night sleep variations. Our participants were racially and ethnically diverse people across the adult lifespan. However, our study was limited by its small, convenience-based sample of participants (74 people) and cross-sectional design. We cannot determine if poorer sleep causes lower neural similarity with this data. 

Taken together, our study suggests that memory integrity, or the ability to clearly remember the details of past events, may be linked with consistent sleep patterns. Thus, in addition to sleeping for enough time, sleep consistency also contributes to better memory retrieval. 

Edited by: Trang Nguyen, Pei-Yin Shih

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