Happy Daylight Savings Time, not! Five steps to help you ease your circadian clock back on track.

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Daylight Savings Time (DST) is back yet again. And not without consequences. The Monday following the time change hosts a 25% spike in the number of heart attacks, a 20% increase in road accidents and a 6% increase in workplace injuries. Why does that 60 minutes have such an impact on our health, performance and safety? The reason is that it messes with our body clock.

Our body has a clock, the circadian clock, which determines when we’re awake or sleepy during the 24 hour day. This clock synchronizes to time cues in the environment, the most important being the 24-hour light/dark cycle of the sun. Indeed, research at my former lab at the Ludwig-Maximilians University in Munich has shown that this synchronization is so sensitive, people wake up earlier as you go east within the same time zone!

DST pushes our social schedule an hour forward, but not the circadian clock, which remains attuned to the sun. This creates a circadian misalignment that is similar to jetlag.  Even though we now have to rise an hour earlier, our circadian clock still wants us to sleep at the same time. Consequently most of us lose an hour of sleep for about a week after the spring transition.

While this affects anyone waking up to an alarm clock, there are steps to help you ease your circadian clock back on track.

  1. Go outside, especially in the morning. Outdoor light in the morning helps you adjust to an earlier wake-up time and bedtime. Take breakfast on your balcony, walk your kids to school, bike to work. Even on a cloudy day, the brightness from outdoor light (~ 1000 lux) far exceeds ordinary home lighting (~50 lux). If it’s still dark outside when you get to work, consider getting a light box.
  1. Don’t wear sunglasses. Light impacts the circadian clock via the eyes – not, as many assume, the skin.
  1. Dim your lights at night. While light is beneficial during the day, it has disruptive effects on your body at night. In particular, blue light interferes with circadian rhythms and melatonin secretion. Use dim yellow or red lights at night, starting three hours before sleep to help adjust to earlier sleep. Also limit exposure to screens three hours before sleep, including smartphones, tablets, laptops and close-range TV’s. Alternatively you can get free software that blocks blue light emitted from your screens at night: https://justgetflux.com/. Or wear blue blocking eyewear (blue blockers).
  1. Toss your melatonin (unless it’s a slow-release micro-dose). Commercially available melatonin (typically 1-10mg) far exceeds the amount your brain naturally produces (0.2mg) and its absorption extends into the next morning. This can shift your sleep cycle in the wrong direction, making you take longer to fall asleep at night.
  1. Make gradual changes. If you can, move your bedtime and wake-up time gradually over the course of a week or two by increments of 15 minutes a time. For those of you who use light therapy, start using the light gradually earlier in the morning, in steps of 15 minutes a time, starting 1-2 weeks ahead of the time change. You can also speed up the adjustment to DST by using the lights for 15 minutes longer than usual during the week before or after the transition to DST.

There is more to light than meets the eye

Light is essential for our circadian clock!

All living organisms, you and I included, have biological rhythms in physiology and behaviour. Our most obvious behavioural rhythm is our daily pattern of sleeping and waking. Other biological rhythms include daily changes in body temperature, hormone secretion, appetite and alertness.

Scientists have shown that these daily rhythms are more than passive reactions to the environment; they are generated by an internal body clock – the circadian clock. Each person’s circadian clock has an innate rhythm that is close to, but not exactly, 24 hours (if you are a late type like me, chances are your clock is a little longer than 24 hours). If you were to stay in a cave for a number of weeks without access to the outside world and knowledge of local time (yes, scientists have tested this!), you would continue your daily rhythms, but these rhythms would slowly drift out of sync with the outside world.

The clock synchronizes to the outside world by means of time cues in the environment, the most important being the light/dark cycle of the sun. A study by the Ludwig-Maximilian University of Munich shows just how important daylight is in the timing of our sleep. While Germany has the same time zone across the country, the timing of its residents’ sleep on free days varies systematically from east to west by about 30 minutes, matching the difference in the timing of sunrise.

When we don’t get enough daylight, our circadian clock fails to properly synchronise, making it vulnerable to drift, just like in a cave.

Light impacts the circadian clock via direct nerve connections between our eyes and the brain – not, as many assume, the skin. So for light to yield its positive effects, you must allow your eyes to absorb the light. If you are tanning at the beach with a cap over your head, you are in the dark, circadianly speaking! So is modern day indoor life. Indoor lighting levels (generally below 400 lux) are extremely low in intensity compared to outdoor light (about 20,000 lux in the shade on a clear blue sky day or about 100,000 in bright sunlight). When we don’t get enough daylight, our circadian clock fails to properly synchronise, making it vulnerable to drift, just like in a cave. This is of particular concern to city dwellers. Research shows that people’s sleep is much more uncoupled from the light/dark cycle in urban areas (population size > 500.000) than in rural areas (population size < 300.000), where people generally spend more time outdoors.

Moreover, receiving light at the wrong time of day (light pollution) can disturb the circadian clock. Artificial light at night, from indoor lighting to electronic devices (e.g. computer or phone screens) suppresses the release of melatonin, essential for sleep. It can also lead the clock to synchronise to the artificial night light instead of daylight (in particular when the latter is in short supply), potentially delaying our sleep into the early morning hours.

Circadian clock disturbances are more than an annoyance! They are closely tied to sleep and mood disorders, unhealthy lifestyle choices (cigarette and alcohol consumption) and in the long run, can have serious consequences to our health, significantly increasing our risk for heart disease, digestive disorders, obesity, diabetes, reproductive problems, and even cancer.

The good news is that you can do something about it. Leave your cave. Or check out www.circadianlighttherapy.com.