Experiments in Jet Lag - Part Two

An Inquiring Mind by Ginny Smith

In part 1 of this blog post, I decided to try using my understanding of circadian rhythms to avoid jet lag on returning to Singapore.

I had originally hoped to begin my experiment before leaving the UK. You can get a head start on beating jet lag by beginning to move your body clock before you leave. This is easy enough in theory- you just change your bedtime and getting up time by an hour or so for the last couple of days before you fly. Unfortunately, this doesn’t always fit in with real life, and the amount of packing we had to do meant I didn’t manage to get to bed early. So I began my experiment on arriving in Singapore, on Thursday evening.

To work out how to use light effectively to counteract jet lag, you need to take into account two things. One is the direction of travel, and so the direction you need to shift it in. When you fly east, from the UK to Singapore for example, you have to move your watch forward, and your body clock needs to do the same. Flying west, like from the UK to the US, or Singapore to the UK, your watch and body clock need to move backwards. So how can you use light effectively to help your body clock get back in sync?

This all revolves around a measure known as Tmin.  On a normal night, this is the point at which at you are in the deepest sleep, and at this point your temperature, which fluctuates throughout the day, drops to its lowest.  For most people this happens a few hours before they wake up- so let’s say around 4 a.m. So what you have to work out when you’re trying to beat jet lag, is when your body thinks its 4 a.m. Then, you base your light exposure on this point.

Whether you need light before or after this time depends on whether you are trying to move your clock forwards or backwards. When I first arrived in Singapore, with my circadian rhythms still matching UK time, my Tmin would have fallen at about midday in Singapore. To match it up with Singapore time, I needed to shift my clock earlier, so Tmin happened during the night, rather than in the middle of the day. To do this, I needed to get light exposure after Tmin, and, vitally, not before it.

An Example of a TMin schedule for a night shift worker. Paper source below.

On my first trip, I hadn’t known this. So, when my alarm went off at 8am, I groggily opened the curtains, letting the light stream in. This is something I always do in the UK, as I find some sunshine (real or artificially created by my daylight lamp) really helps me wake up in the morning. What I didn’t realise was that this was backfiring. Because my Tmin, hadn’t occurred yet, my body thought it was still night-time, not the morning. So bombarding it with light would actually have moved my circadian rhythms later (generally, light in the evening delays the body clock). Of course, I then experienced light throughout the day, so it did also receive light after Tmin, but these mixed signals are likely to have made it harder for my body to adapt.

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This is a particular problem when flying east. When flying west, you need light before your Tmin, to delay your clock. And this is usually what happens naturally. When I came back from Singapore last time, my Tmin, would have been at around 8pm U.K. time- so just by exposing myself to daylight during the day, I would have light before this point and not after. This is exactly what I needed to delay my body clock, and this is one reason I had fewer issues adapting after returning home.

Back to my current trip and I needed to ensure I had lots of light after Tmin, and very little before. So, on the first day, Friday, with my Tmin, happening around midday, I had to keep the curtains closed for as long as possible in the morning. So that’s what I did. I also set my laptop to night mode, making the screen dimmer and red-tinged (blue light resets the body clock most efficiently). When I needed to venture out for some breakfast, I wore my sunglasses, even though we were staying within the hotel. Did I feel a bit silly? Yes. But if I was going to do this, I was going to do it properly.

Using this technique, it should be possible to shift the body clock by about an hour each day. So that meant on Saturday I only had to lurk in the gloom until 11am. Then 10 on Sunday and 9 on Monday. It was pretty annoying for the first few days- the temptation to open the curtains to glorious sunshine was really high, especially after a month of dreary winter weather in the UK! It was also tricky to get bright light straight after- on the first couple of days, by the time I was allowed light it was too hot to be outside for long. And on Sunday it started raining within a few minutes of me opening the curtains. This was annoying as studies have shown that the few hours after Tmin, are the time when light can most effectively shift our circadian rhythms. But I stuck with it and did my best to follow my schedule- and I think it helped!

While I didn’t sleep through the night, waking up around 2am for the first few nights, and sleeping a bit less deeply for the next couple of hours, I didn’t have the terrible middle-of-the-night insomnia I endured last time. And I definitely think I felt a bit perkier when the alarm went off- probably partly due to a direct reduction in jet lag, and partly down to getting more sleep! Last time, it took me a week or more to feel properly human again after landing, whereas this time I was fully functioning a few days sooner.

So would I recommend following one of these plans? It depends. There are calculators online that will help you work it out, which is really helpful. It’s simple to put in your usual sleep & wake times, and receive your own Tmin, and a routine to follow. The problem is that, for the first few days at least, you miss out on a few hours of enjoying yourself in your new home. If you are only there for a short time or having to attend work meetings, it would be difficult to follow the regime properly. Yes, you could wear sunglasses and a hat to your meeting, but I’m not sure how well that would go down with most bosses! So, I guess it’s something each person will have to decide for themselves, for each trip. Which will be more inconvenient – the jet lag, or the treatment to cure it!?

  • Sleep Cycle chart from Smith, Mark & Eastman, Charmane. (2012). Shift work: Health, performance and safety problems, traditional countermeasures, and innovative management strategies to reduce circadian misalignment. Nature and science of sleep. 4. 111-32. 10.2147/NSS.S10372. 

Ginny Smith is a science presenter and writer. A Natural Sciences and Psychology graduate of Cambridge, Ginny performs science shows all over the world and presents a wide range of science content for the likes of the Cosmic Shambles Network and the Naked Scientists. She is the co-author of three DK Publishing science books and her first major solo work, Overloaded, will be published by Bloomsbury in 2021. She is @GinnyFBSmith on Twitter.

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