Jonas talks about the benefits of morning light for our health — The Peach

How getting more natural light in the morning benefits our health — A reason to get up and out in the morning

We evolved spending most of our time outdoors, bathed in natural daylight. These days, we wake up indoors and spend most of our day indoors. But natural daylight benefits us in ways that artificial light does not.

Could 10 minutes outside in the morning be better for our sleep than 10 minutes more in bed?

The amount of daylight we get has implications for our wellbeing, alertness, sleep duration and quality. Getting morning light (before around 10am and even if it is cloudy) is crucial for optimising our circadian rhythm. But how does it work?

The circadian rhythm, our internal metronome

Our internal circadian rhythm is an approximate (circa) daily (dies) rhythm; we have complex internal clocks running our daily sleep and wakefulness rhythm. Because of these internal clocks, we would still have an almost perfect 24 hour sleep-wake cycle, even if we were to live in a cave without natural light. But this internal cycle isn’t precisely 24 hours in length, so to keep in line with one complete rotation of the Earth around its axis (a day and a night), we need exposure to natural daylight. This also helps us to adapt to the different day lengths of different seasons and in different parts of the world. The process of resetting our circadian rhythm by exposure to natural light is called circadian photoentrainment.

Receptors in our eyes called melanopsin receptors react to light intensity and light wavelength and send information to the brain, triggering various pathways that affect alertness, wakefulness, sleep quantity, quality and mood, thereby further influencing our circadian rhythm. This rhythm is most sensitive to the effects of natural light shortly after waking and to almost any form of light before going to bed and during the night. Light quality changes after around 10am, as does our own receptivity, meaning that catching morning light matters. Once early morning has passed, the impact of natural light on our receptors is minimal until much later in the day.

Why early morning light and why outdoors?

It is both light intensity and the wavelength of light that matters to our melanopsin receptors. Whilst our vision adjusts to brightness, so we may not be conscious of the difference in light intensity between being indoors and outdoors, it is nevertheless better to experience early morning light outside, even if it is cloudy. Light is measured in lux. Full sunlight can give us about 30,000 lux. On a cloudy day, light intensity can reduce to around 10,000 lux. In a brightly lit room, we may experience 500 lux. And experiencing natural light from indoors reduces the impact on our melanopsin receptors significantly. For optimal melanopsin receptor activation, we need the higher lux levels we can obtain from being outside.

Morning light is particularly important because the wavelength of natural light changes throughout the day. Very early in the morning and late at night, the wavelength is much longer so that there is plenty of red light (wavelength dictates the colour of visible light), which doesn’t significantly affect our circadian rhythm. Once the sun has started rising, blue green light levels increase and it is this shorter wavelength light which has the strongest influence on our circadian rhythm via melanopsin receptors, suppressing melatonin secretion and setting us up to be alert for the day.

The role of hormones and neurotransmitters on our circadian rhythm

The neural signals from the melanopsin receptors are processed in the suprachiasmatic nucleus, which is a part of the hypothalamus in the brain. It is often referred to as the central pacemaker of the circadian rhythm and it regulates most circadian rhythms in the body. This central pacemaker is influential in many ways, including influencing the release of cortisol and melatonin and being influenced by a neurotransmitter called adenosine.

Melatonin is a hormone released by the pineal gland in the brain. Pineal gland activity is influenced by the suprachiasmatic nucleus. Melatonin functions as a signal to other areas of the brain to get ready for sleep, but also has positive anti-inflammatory, antioxidant and neuroprotective properties. Early morning natural light not only suppresses melatonin secretion, it also increases cortisol levels and both of these actions aid with alertness. Although cortisol is often mentioned in connection with long term stress, it has a crucial role in your daily wakefulness-sleep rhythm. Elevated cortisol levels in the early morning help us to wake up and set levels of alertness and mood. Cortisol levels tend to decrease over the day to a low point between 2-4am. Whilst cortisol levels fluctuate without exposure to natural morning light, being exposed to natural light early in the morning helps to trigger the optimal cycle of cortisol release to make us alert in the day and be able to sleep well at night.

Adenosine is a neurotransmitter involved in the sleep wake cycle. This molecule builds up throughout our wake cycle and inhibits excitatory action in the brain. The longer we are awake, the more adenosine we accumulate; the greater our desire for sleep (sleep drive or sleep pressure). During sleep, adenosine levels drop. When significant levels of adenosine have built up, late night light exposure is less likely to prevent us from sleeping.

Seek early morning light, but shun any light late at night

Early morning natural light exposure not only suppresses melatonin production at that time, it also sets a timer for melatonin secretion later that evening, helping to ensure you are ready for sleep in the late evening. However, any sort of light exposure late in the evening/night inhibits melatonin release, causing us difficulties falling asleep as well as risking poor sleep quality. In the morning, we want exposure to light, particularly blue green light, but in the evening, we want to avoid exposure to light. Blue green light filters are not enough to protect us from the negative effects of night light exposure, because light with other wavelengths to blue green light can still indirectly affect receptors to inhibit melatonin secretion, causing us to struggle to get to sleep. So, for optimal melatonin cycling, we need to see natural morning light before around 10am and we want to avoid exposure to any sort of light between 10pm and 4am. Red light has been found to affect our circadian rhythm less, so if you need light at night, it might be worth considering using red light.

Effects of caffeine on our circadian rhythm

Caffeine works to block adenosine receptors so that adenosine cannot bind to increase sleep drive in the same way. This partly explains the stimulating action of coffee and other caffeinated beverages. Most people who drink coffee or caffeinated tea usually wake up with the thought of coffee or tea in their mind. But drinking caffeinated drinks soon after waking might not be a great idea. Elevated cortisol levels naturally occur in the morning, moving us to wakefulness and alertness. Caffeine can interfere with cortisol production and, in so doing, interfere with our circadian rhythm. Likewise, drinking caffeine when morning cortisol levels are rising can mute caffeine’s stimulating effect, meaning we may build a greater tolerance to it, requiring more caffeine for the same stimulating effect. It is best to wait at least an hour after waking before consuming caffeine or, if later, until after 10am if possible.

Our complex dance with light

Our wakefulness and sleepiness depend on us experiencing natural light outside early in the morning and avoiding bright light late at night. Our bodies have their own internal clocks, on a cellular level, tissue level and as a whole organism, but these internal clocks, governed by the suprachiasmatic nucleus, rely on natural light to stay aligned with the Earth’s day and night cycle. There are various hormones and neurotransmitters involved in this including cortisol, melatonin and adenosine. Other players, such as dopamine, serotonin and testosterone are also involved. To keep your body clock aligned so that you can feel alert and attentive throughout the day and sleepy at night, go outside and experience the morning light. Delay caffeine intake until late morning and let your body wake up naturally. See how you can shift your routine to make time to do this.

One word of warning though, staring directly at the sun or into very bright light to cause discomfort is a bad idea. The famous Isaac Newton once experienced this when he tried to stare at the sun through a mirror, allegedly blinding himself for three days and experiencing afterimages for months. This is not the goal!

Although I do not have a garden, I feel very fortunate that my landlord has some old railway sleepers at the end of his field, where I can sit and enjoy the early morning light. I have come to relish my little ritual of taking my morning breakfast and tea outside most days.