How to use light to fix your broken sleep

One of the hardest aspects of being an emergency physician is the constant rotation of your work schedule, it is truly the furthest thing from a 9-5 job possible. The thing that is particularly challenging about it is sleeping adequately during the day after a night shift - it just never feels like I wake up feeling fully rested. Needless to say, I've put a lot of thought into how to approach night shifts and the forever-evolving schedule I navigate.

I've read a bunch of research to try and find ways to crack the code on sleep and shift work. One paper that really stood out to me was written by a team of researchers at Rush University in Chicago. The group started the Biological Rhythms Research Laboratory and seems to be among the most prolific in the field of sleep science. The paper that drew my interest is titled Complete or Partial Circadian Re-entrainment Improves Performance, Alertness, and Mood During Night-Shift Work by Crowley et al.

Here's how the basic study went:

67 young healthy adults made up the group being studied. The team went into the participants' homes and blacked out the windows in their bedrooms and even installed air conditioners if they didn't have one!

It was a total of two weeks for each participant - the first week was just recording baseline sleep for each person. The second week each participant worked five consecutive "night shifts" where they went to the research lab where they had salivary melatonin levels measured every 30 minutes between 6:00PM and 3:00AM, took cognitive performance tests on the computer, and filled out questionnaires about how sleepy they felt, how their moods were, etc. They would then go home to sleep and would record their sleep in a journal. They also wore an activity tracker that would record their sleep and a light meter that recorded the ambient light they were exposed to night and day.

The participants were split up among four different treatment groups: half were exposed to pulses of bright lights during the night shift and half worked in dim light. Half wore normal sunglasses driving home and half wore dark sunglasses. So the groups were dim light & normal sunglasses, dim light and dark sunglasses, bright light & normal sunglasses, and bright light and dark sunglasses.

Each participant was also given a pill which was either 1.8 mg melatonin or a placebo - taken just before daytime sleep.

Metrics of Interest

The overall idea is that to optimize sleep after a night shift, you need to delay the sleepiest phase of your circadian rhythm until you go to bed during the daytime. This is what researchers call the "temperature minimum", thought to be about 7 hours after your body starts secreting melatonin as the sunsets. This time varies and is thought to contribute to "early risers" or "night owls". They found that this has a pretty significant effect on who was able to adequately shift their circadian rhythm.

Overall, people who were able to even partially re-align their circadian rhythm with the periods of daytime sleep had significant improvements in all measures; cognitive performance, mood, and energy levels. They found that the most important variable predicting success was an individual's baseline circadian rhythm on night one of the night shifts. Those whose sleepiest times occurred before driving home in the morning benefited the most from bright light pulses during their shifts and dark sunglasses on the way home. The bright lights delayed their circadian rhythm and the dark sunglasses prevented daylight from waking them up.

Duration of sleep didn't seem to have any effect - even if you slept all of the 7 hours they allowed, you still felt terrible if you didn't realign your circadian rhythm. Even worse, subjects who didn't re-align felt worse each night while those who had re-aligned didn't see a drop.

Interestingly, melatonin didn't seem to help shift subjects' sleep phase.

Good Light/Bad Light

I found this paper interesting because of its practicality. I like that they created a protocol that is translatable in the real world. They specifically chose a 7 hour daytime sleep period because they felt that most people aren't able to actually get a full 8 hours - which is definitely true from my experience.

To me though the most important point is how to approach night shifts based on your particular sleep "profile". If you're a night owl, you're going to have an easier time re-aligning your sleep physiology with the actual period of sleep you're able to get. If you're an early riser, it's going to take a more concerted effort to maintain exposure to adequate lighting on shift and to be vigilant on the way home with very dark glasses - blue blockers if ya' got 'em.

One other point they make is that older people have a more difficult time re-aligning their circadian rhythm which means it will only take more work to be rested on night shifts as I get further along in my career. That's no surprise though, night shift work is among the most common reasons for burnout among emergency medicine doctors.

My Take-Away

I'm generally someone who does better when getting up relatively early in the morning. I need the extra support to help shift my circadian rhythm when I'm on a stretch of night shifts. As a resident, it wasn't uncommon to work 4, 5, or sometimes 6 straight nights. As an attending that's much less common and usually is one or two, sometimes 3 nights. There isn't as much opportunity - or benefit - to fully flipping your sleep schedule.

To help optimize my sleep though I'm going to be more intentional with how I use light. I'm going to definitely wear sunglasses after shift. I think it's worth trying bright light exposure while on shift also. It's easy to set up a light next to the computer and turn it on once in a while on shift. There are other times when light exposure is helpful also, specifically when you've been working late evenings or overnight and need to flip back to early day shifts. More recent research from the same group showed bright light exposure immediately after waking up and a small dose (0.5 mg) of afternoon melatonin helped to advance the circadian rhythm and promote an earlier bedtime.

Sleep is challenging when your schedule is constantly changing. It's easier to be nonchalant about it in your late 20s and early 30s. It's a serious obstacle to wellbeing as you go through your career in emergency medicine (or any career with shift work). It's worth taking small steps to improve your sleep and being intentional about your approach may pay dividends down the road.