Before we talk about the sleep homeostat, let’s briefly visit the circadian part. When we travel west across time zones, we “gain” time before bed, in a sense, as the destination clock time is earlier compared to the home (departure) zone. Many people find such travel easier to manage, since it seems easier to stay up later than usual for many of us. But when we travel east across time zones, that is harder for most people, since it seems harder to go to bed earlier than usual. As far as wake up times, traveling west is awesome because we can sleep in (at least theoretically) compared to home – but traveling east is a bummer because we need to get up earlier than we are used to. This is all roughly true for typical travel of 2-8 time zones. The more the time zone change, the harder it is to adjust in general, and as we approach 12 hours of change, the direction of travel plays less of a direct role. Techniques to reduce jetlag that target the circadian system involve schedule shifts (moving your sleep schedule gradually over several days prior to travel to approach the destination zone), light exposure (to match ideal times or at least avoid counter-productive times of bright light), and sometimes also taking melatonin. Sites like www.jetlagrooster.com are useful for this kind of advice.
Now, back to the homeostat. This clock starts ticking when you wake up, and keeps track of how long you’ve been awake. For a person who typically sleeps from, say, 10pm to 6am, when night rolls in, there are two clocks say it’s time for sleep: the circadian clock that pays attention to the actual clock on the wall, and the homeostatic clock that says “you’ve been awake since 6am, so yes, you can sleep now”. Fun fact: when you drink coffee, it is thought that the caffeine tricks the homeostatic clock into thinking you have not been awake as long as you have. The homeostatic clock can also be “tricked” by naps. If you are a 10pm to 6am kind of person, and you happen to take a nap late in the day, say, from 7-9pm, the homeostatic clock senses the recent sleep, so it might be difficult if you try to sleep again at 10pm.
How does this relate to jet lag? Well, let’s say you are flying east, across 5 time zones, and you land at 9pm in the destination time zone. Say you are hoping to be in bed shortly thereafter, by 10pm. Your circadian system does not like this, because it is only 5pm in your home zone, which it is accustomed to. Well, let’s also say you happened to also doze for 3 hours, in the second half of the flight. Now, your homeostat is also not happy, since you just slept recently, before trying to go to bed at 10. You have two clocks working against you! The point is, depending on the time of day you are landing in the destination time zone, you would be wise to plan your in-flight dozing to please your sleep homeostat. For evening destination landings, you’d be wise to limit your in flight sleep, and if you do sleep, try to front-load it at the beginning of the flight, so you have been awake for a while upon landing, and have built up some homeostatic drive to sleep. This thinking applies to morning arrivals as well: in that case, sleep as much as you can and as close to landing as you can, so you wake up with your homeostat on your side to maintain alertness during the day at destination.
Contributed by: Dr Matt Bianchi.