How light and darkness changes sleep and behavior? 

There is a particular kind of tiredness that arrives with the darker months. It is not always the tiredness of a late night. It is the alarm going off at exactly the same time as it did in August, and somehow feeling far more offensive. It is three in the afternoon suddenly looking like evening. We all know the feeling, the desire for another coffee, the feeling of less patience, and a body that seems to be asking for warmth, sleep and carbohydrates all at once.

Every winter, some version of the same question appears: why am I so tired?

The more interesting answer is what that darkness does to us? The human body reads light as a cue. It always has done so, long before clocks, alarms, office hours and electric lighting, daylight was one of the clearest ways, we knew where we were in daytime.

We still work like that.

The 07AM problem

There is a reason the same alarm feels different in November, compared to June. In late autumn, particularly this far north, you can be asking the brain to become fully awake while everything outside still looks like night. The clock says morning, but the environment says otherwise. This is where we get something important wrong about sleep. We think the clock is in charge. It is not. The body is paying attention to light. 

So when people tell me they are finding mornings harder in winter, I do not immediately think they have suddenly become bad sleepers. I think: the signal has changed. The light signal is weaker, and we can feel it.

Light is not decoration

Our circadian rhythm is often described as an internal clock. I think it is more useful to think of it as a timing system that is constantly negotiating with the outside world.

Light is one of its strongest inputs.

Morning light supports alertness and helps anchor the biological day, as evening becomes darker, melatonin rises and the body begins moving in the other direction. Melatonin is often called the sleep hormone, but really it is closer to a signal. It tells the body what part of the 24-hour cycle it is in. This is why sleep never really starts at bedtime, it really starts with the first glimpse of daylight. 

The winter contradiction

The problem with winter is not that it gets dark. We need darkness. The problem is that we have become very good at removing the difference between day and night, so our internal system can not tell the difference between day and night. We wake before sunrise. Travel to work in the dark. Sit inside for most of the daylight hours. Then, just as the natural world becomes dark, we switch everything back on. Kitchen lights. Bathroom lights. Laptops. Televisions. Phones.

Our days have become dim and our evenings have become bright. Biologically, that is an odd arrangement, which affects how we sleep. A grey Copenhagen morning may not feel particularly bright, but outdoor light is still a very different signal from ordinary indoor light, and our body does not need the weather to be beautiful, we need contrast.

Day should look like day.

Night should look like night.

The carbohydrate question

Then there is the food. Every winter, the same cravings seem to arrive with the darkness: bread, pasta, something warm, something sweet. There is biology behind at least part of this. Increased appetite, carbohydrate cravings, tiredness and longer sleep are all well described in people who experience stronger seasonal changes in mood, including seasonal affective disorder.

That does not mean every bowl of pasta in November needs a circadian explanation, but it does expose something we often forget: sleep, appetite, mood and metabolism are not separate departments. We talk about them that way because it makes health easier to organise. Sleep over here. Nutrition over there. Stress somewhere else. The body has never agreed to this filing system, in reality a poor night can change hunger the next day. 

The body experiences one continuous day.

The night starts in the morning

Most sleep advice begins at night, but mine often starts much earlier. If winter is making you feel slower, get outside early in the day. Walk around the block and drink your first coffee outside. Take the first call while moving. Walk part of the way to work. It does not need to become a ritual. You are simply giving the brain information it is looking for: this is daytime.

And because winter daylight is scarce, use it while it is there. If you have spent the morning inside, go out around lunch. 

At night, do less

We spend an extraordinary amount of money trying to add things to sleep; Supplements, trackers, special routines. Another piece of technology to tell us whether the previous piece of technology thinks we slept well, but sometimes the more useful intervention is actually subtraction.

Sleep is a transition.

Good evenings make that transition easier.

What winter reveals about sleep

Winter makes one thing unusually easy to see: sleep is not an isolated event. The night is built across the day. At MUUN, this is why we think about sleep as a system rather than eight hours removed from the rest of life, and certainly not as a mattress alone. The bed matters, of course.

So do light, temperature, sound, timing, movement, food, stress and whether the body has actually been given permission to stop. Good sleep design is often quiet. It gives the body clearer signals and then gets out of the way. Perhaps that is the more useful way to think about winter sleep - via signals of light and darkness. 

Source inspiration / research starting point: https://theconversation.com/tired-irritable-and-craving-carbs-why-darker-days-affect-our-bodies-and-brains-295124