One of the surprises of this that the circadian clock operates in essentially all cells that contain a nucleus, not only specialized cells in the brain, allowing PER and TIM to “affect other aspects of physiology” with “implications for work schedules, sleep hygiene,” and more, ushering in the field of chronobiology.

in REM sleep, our emotional centres are overstimulated while our reflective rational centres are impeded or narrowly refocused on issues of emotional significance. We are left free to ponder the endless meanings of the emotions and interactions that we experience but we do so with wildly fluctuating levels of reflective insight ... The neurochemistry of dreams produces an emotionally intense state of mind in the absence of an ability to critically reflect on the images produced by that state.

The calories consumed later in the day are more likely to be stored as fat ... When people eat at a time when the liver has packed it in for the night, those sugars and fats are not properly metabolised. Twenty percent of liver proteins are created in a strictly circadian fashion, so that the liver produces twice the average number overall in peak times, and half at the lowest times. If one stifles those clock genes in the liver, fat levels in that organ spike, even with a low-fat diet.

Sixty percent of people sleep with another person. When one person has sleep issues, both can suffer ... Research into couples’ sleeping patterns reveals a curious dynamic. When objective measures like brain waves or eye movements are examined, people are found to generally sleep better when they sleep by themselves than when they sleep with a bed partner. Yet when they’re asked about sleeping alone, people say they are less satisfied.

there is a link between a disruption in circadian rhythm and known metabolic risk factors for obesity, diabetes, and cardiovascular diseases ... This link arises because disruptions in circadian rhythm muck up our microbiome, bacteria in our gut that help us digest our food. Beyond diet, they may also be affected by our mealtimes. A disturbed host’s clock disrupts the microbes’ 24-hour rhythm—reflected in their composition and overall function

People who get less than six hours of sleep a night may be more likely to have risk factors that increase their odds of diabetes, heart disease and strokes, a Korean study suggests.

humans may have evolved to sleep during the coldest hours of the day, perhaps as a way to conserve energy ... If falling temperatures at night are a signal to our bodies that it is an ideal time to go to sleep, then that could be one reason chronic insomnia is so prevalent in industrialized societies.

Experiments have long shown that people who get a good night’s sleep are better able to recall what they learned the day before than those who don’t ... During sleep, the brain rebalances both the immune and endocrine systems; that’s why sleep disorders are associated with ills including depression, obesity, diabetes, cardiovascular disease and cancer. Tinkering with the controls might have nasty consequences.

Most adults are fine with about eight hours of sleep, but toddlers need around thirteen hours, including a daytime nap. Teens need around nine and a half hours; what’s more, they tend to be night owls, whose ideal circadian rhythm has them going to bed and waking up late...the health effects on students have been severe...It’s not just sleep loss. It’s circadian disruption...Waking a teen at six in the morning is like waking an adult at three at night.

chronic sleep restriction increases levels of appetite and stress hormones; it also reduces one’s ability to metabolize glucose and increases the production of the hormone ghrelin, which makes people crave carbohydrates and sugars, so they get heavier, which in turn raises the risk of sleep apnea, creating a vicious cycle.