The Vitals: Sleep Series Part 1

Why Do We Need It?

The truth is that the reason we sleep is largely a mystery. We know that lack of sleep can be detrimental to long term health and that acute sleep deprivation can lead to disordered thinking, poor impulse control, delirium, hallucinations, and, if you get behind the wheel after a long shift, perhaps death. In fact, according to the CDC, being awake for at least 24 hours is roughly equal to having a blood alcohol content (BAC) of 0.10%! That’s higher than the 0.08% BAC legal limit in all 50 states. So while we are not sure why we sleep, scientists have proposed a number of theories.

1) Evolutionary or Inactivity Theory: We sleep because of evolutionary pressure that allowed those who were inactive at night to escape predation, injury, or death in the dark. In other words, hiding away and sleeping for the night prevented us from becoming another predator’s midnight snack.

2) Energy Conservation Theory: Sleep allows us to reduce the body’s energy expenditure during the time of day and night when it is least efficient to search for food. In fact, the body’s metabolic rate decreases by 10% while we sleep, so you might want to think twice before you scarf down that cupcake before bed.

3) Repair and Restorative Theory: While we sleep, the body replenishes and repairs cells and their components, from protein synthesis to muscle repair and tissue growth, which are consumed during the various metabolic processes during the day. Which explains why you never got that six pack you wanted during residency… Got to sleep to grow, baby!

4) Brain Plasticity or Information Consolidation Theory: Sleep helps us consolidate long term memory because that is when our brains are able to reorganize their neural structure and grow new connections. Perhaps that’s why you never seemed to recall anything you studied during your late-night cram sessions in medical school. 

5) The Brain Clean Up Theory: One of the newest theories devised, the glymphatic system was identified by researchers at the University of Rochester in 2013 as a macroscopic waste clearance system that removed cellular metabolites and proteins from the central nervous system. The glymphatic system also seemed to be responsible for distributing glucose, lipids, amino acids, neural hormones, and growth factors throughout the brain. The remarkable aspect is that the glymphatic system was most active during sleep when extracellular space expands so that efficient removal of neurotoxic waste products such as beta-amyloid can occur. It has since been proposed that the restorative function of sleep is due to nightly clearing of the waste that our awake brains have left behind. It’s kind of like deleting your brain’s Google search history, except your partner won’t find it.

Of course, there are many more hypotheses for the reasons why we sleep and like many things in science, the true answer is probably some combination of these theories. But it is indisputable that getting sleep is paramount to optimal function and health. Next time, we will hone in on sleep in the ICU: why it’s important, what happens when our patients get poor sleep, and how we can promote better sleep. But until then, please please please turn off the TV in your patient’s room and don’t get behind the wheel after a 24 hour shift.