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Sleep

4 Reasons Why You Can Wake Up Tired

Waking up sleepy is only partly your fault.

Key points

  • Getting a good night's sleep requires a balance of internal and external factors.
  • Internal factors include the role of diet and alterations in brain chemistry.
  • External factors include the environment, circadian rhythms, and sleeping partners.

The alarm rings, you awaken, and you are still drowsy. Why? Being sleepy in the morning does not make any sense; after all, you have just been asleep for the past eight hours. Shouldn’t you wake up refreshed, aroused, and attentive? No, and there are a series of ways to explain why.

The neurobiological answer

During the previous few hours before waking in the morning, you have spent most of your time in REM sleep, dreaming. Your brain was very active during dreaming and quickly consumed large quantities of the energy molecule ATP. The “A” in ATP stands for adenosine. The production and release of adenosine in your brain are linked to metabolic activity while you are sleeping. There is a direct correlation between increasing levels of adenosine in your brain and increasing levels of drowsiness. Why? Adenosine is a neurotransmitter that inhibits, i.e., turns off, the activity of neurons responsible for making you aroused and attentive. You wake up drowsy because of the adenosine debris collected within your brain while dreaming. The only known cure for too much adenosine is coffee.

Who did you sleep with last night?

Couples sleeping in pairs were investigated for sleep quality, that is, for the correct balance of non-REM and REM, as well as their own subjective view of how they slept. For women, sharing a bed with a man harmed sleep quality. However, having sex before sleeping mitigated the woman’s negative subjective report, without changing the objective results—that is, her balance of non-REM and REM was still abnormal. In contrast, the sleep efficiency of the men was not reduced by the presence of a female partner, regardless of whether they had sexual contact. In contrast to the women, the men’s subjective assessments of sleep quality were lower when sleeping alone. Thus, men benefit from sleeping with women; women do not benefit from sleeping with men unless sexual contact precedes sleep—and then their sleep still suffers for doing so.

Did you go to bed late last night?

Too many people go to bed too late on too many nights. The reason is that going to bed later just feels better; in addition, we tend to fall asleep faster if we delay going to bed. Going to bed one hour later every night is easier than going to bed one hour earlier. Why? Because humans evolved an endogenous biological clock that is set for 25 hours while we live in a world that functions on a strict 24-hour cycle. This means that it is always easier to go to bed one hour later. People who prefer to stay out late (evening types) get up at a later time and perform best, both mentally and physically, in the late afternoon or evening. Unfortunately, evening-type individuals were also significantly more likely to suffer from poor sleep quality, daytime dysfunction, and sleep-related anxiety as compared with morning-type individuals. Even more disconcerting is that late bedtime is associated with decreased hippocampal volume in young healthy subjects. Shrinkage of the hippocampus has been associated with impaired learning and memory abilities.

Did you go to bed hungry last night?

What you eat before bedtime also might improve your chances of getting a good night’s sleep. A recent study suggests that eating something sweet might help induce drowsiness. Elevated blood sugar levels have been shown to increase the activity of neurons that promote sleep. These neurons live in a region of the brain that lacks a blood-brain barrier; thus, when they sense the presence of sugar in the blood they make you feel drowsy. This might explain why we feel like taking a nap after eating a large meal. This is just one more bit of evidence demonstrating your brain’s significant requirement for sugar to maintain normal function.

Getting a good night’s sleep is not always easy for most people. With aging, normal sleep rhythms become increasingly disrupted leading to daytime sleepiness. Scientists have determined that we sleep best at puberty; then, sleep quality declines with age.

What if you do not get enough sleep?

Although scientists have not discovered why we sleep, they have discovered that we need between six and eight hours every night. Not getting enough sleep makes us more likely to pick fights and focus on negative memories and feelings. The emotional volatility is possibly due to the impaired ability of the frontal lobes to maintain control over our emotional limbic system. We also become less able to follow conversations and more likely to lose focus during those conversations. Sleep deprivation impairs memory storage and also makes it more likely that we will “remember” events that did not actually occur. Extreme sleep deprivation also may lead to impaired decision-making and possibly visual hallucinations. Not getting enough sleep consistently places you at risk of developing autoimmune disorders, cancer, metabolic syndrome, and depression. Why? Some recent studies have reported that sleep is important for purging the brain of abnormal, and possibly toxic, proteins that can accumulate and increase the probability of developing dementia in old age.

Whatever you are doing right now, stop and go take a nap. Preferably alone.

Facebook image: PeopleImages.com - Yuri A/Shutterstock

References

Wenk, GL. Your Brain on Food: How Chemicals Control Your Thoughts and Feelings. Oxford University Press, 3rd Edition.

Wenk, GL. The Brain: What Everyone Needs to Know. Oxford University Press.

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