If you pull together all of the recent scientific studies on sleep and melatonin... we've discovered that melatonin only increases the speed with which you fall asleep by 3.9 minutes and only increases the quality of your sleep, or what we call your sleep efficiency, by just 2.2%.

A cup of coffee in the evening can decrease the amount of that deep non-rapid eye movement sleep by somewhere between 20-40% at night. And for a spot of context, I'd have to age a healthy adult by probably about 10-15 years to produce that kind of a reduction in deep sleep.

One study published several years ago examined over 30 different suppliers of melatonin. Relative to what was stated on the bottle, concentrations in each one of the pills ranged from 83% less than that listed to 478% more than what was stated on the bottle.

More recently, we've discovered that REM sleep is significantly associated with your longevity, and the less REM sleep that you have predicts a shorter lifespan.

Your brain and your body need to drop their core temperature by about 1 °C, or about 2-3 °F, in order for you to fall asleep and for you to stay asleep across the night. And this is the reason why you will always find it easier to fall asleep in a room that's too cold than too hot.

If you have a cup of coffee at 2 PM, it would be the equivalent of getting into bed at midnight, and just before you turn the lights out, you swig a quarter of a cup of coffee and you hope for a good night of sleep. And it tends not to happen.

Naps as short as 26 minutes offered a 34% improvement in task performance and more than a 50% increase in overall alertness.

The optimal temperature for sleep at night, for the average human adult at least, seems to be somewhere between 16-18 °C or somewhere between, if I'm doing my mathematics correctly, 61-65 °F.

Relative to their morning type counterparts, evening types are 2-3x more likely to be diagnosed with depression, 2-3x more likely to experience feelings of being depressed for weeks in a row, and also 2-3x more likely to have lost interest in most things that feel good in life. Unsurprisingly, and as a result, evening types are twice as likely to be using antidepressants relative to morning types.

If you limit people to just 6 hours of sleep a night or 5 hours of sleep or even 4 hours of sleep a night for several days or even several weeks, there is a common outcome: They will consistently eat more food relative to those same individuals when they're getting a full night of sleep.

If you are struggling with sleep at night, do not nap during the day. Instead, stay awake across the day and build up as much of that healthy sleep pressure as possible to set yourself up for the best chance of both falling asleep and staying asleep.

And indeed, if I were to place electrodes on your head, I could show you this reliable drop in your brain's physiological alertness that happens each and every afternoon. And what this means is that us humans may not have been designed to sleep in a single bout at night, which is what we call monophasic sleep. Rather, we may have been designed to sleep in two bouts. In other words, one longer bout at night and then a siesta-like nap in the afternoon.

All stages of sleep are critical. Different types of sleep perform different functions for the brain and the body at different times of night. But we need all of those stages of sleep—there is no one stage of sleep that's more important.

Levels of the hunger hormone, which is ghrelin, will rocket up when you're not getting sufficient sleep; they will increase by up to 28%.

In the small island of Ikaria in Greece where siesta naps have remained to this day, men are nearly four times as likely to reach the age of 90-years-old relative to their American male counterparts.

When we've had a few drinks in the evening, we tend to think that we fall asleep more quickly, and in reality, all we're actually doing is losing consciousness more quickly.

Some people will tell me, 'Look, I am one of those individuals, and I can have an espresso with dinner, and I fall asleep, and I stay asleep. So, no harm, no foul.' Well, yes, and no. Even if you fall asleep easily and then you stay asleep across the night, caffeine will still decrease the amount of deep sleep that your brain can generate.

Recommendations typically suggest limiting yourself to somewhere between 1-3 cups of coffee each day. And, ideally, try to cut your caffeine consumption off at least 12 hours before you wish to go to bed at night.

One way that we can ease that process of waking up is trying to warm up the ambient temperature of the bedroom in the last 30 minutes before your alarm goes off.

Your chronotype is strongly determined by your genes. And therefore, it's somewhat hard-wired at birth. In other words, your chronotype fate is genetically predetermined and deep-rooted to a degree.