By Jamie Scott
As previously mentioned, there is much focus on melatonin as our primary ‘sleep hormone’ because of the association of low levels of melatonin and poor sleep architecture (such as delayed sleep onset or an inability to stay asleep for long). This often leads to people trying to boost melatonin levels via supplementation (either with melatonin directly, or its amino acid precursors) immediately prior to their intended sleep time, either as an everyday sleep aid, or when travelling between time zones and trying to stave off the worst of the associated jet lag. Melatonin, however, is most potent when produced endogenously as a downstream product of our daytime physiology and bright light exposure, specifically, its precursor, serotonin.
A neurotransmitter, serotonin is involved in regulating mood, appetite, memory and learning, and, important to this discussion here, sleep. Exposure to bright natural light (especially early in the morning) boosts serotonin production (in conjunction with the amino acid tryptophan and other vitamin and mineral co-factors consumed via a protein-rich breakfast), providing the raw materials for the melatonin required for our night-time physiology at the other end of the day. The converse is also true. The low melatonin leads to poor sleep train of thought is actually one of low morning light exposure plus a low protein intake (leading to low tryptophan and co-factor intake) leads to low serotonin production, which leads to low melatonin production, which leads to poor sleep. Already low melatonin can be further reduced by the already mentioned night-time blue-light exposure (light-induced melatonin suppression, LIMS).
The low melatonin story doesn’t end with sleep disruption. Indeed, melatonin performs a variety of functions in the human body. In addition to its regulatory role in our light-dark physiology, melatonin has antioxidative capacity, immunomodulatory potency, and appears to be protective against a variety of cancers, especially breast and prostate cancer. Melatonin receptors are also located in the ovaries, blood vessels, and intestinal tract. The binding of melatonin to its receptors on the pituitary gland and the ovaries appears to play a role in regulating the release of reproductive hormones in females. For example, the timing, length, and frequency of menstrual cycles in women are influenced by melatonin. Melatonin, in non-human mammals at least, also helps to signal the season and cue mating.
Serotonin, as a daytime neurohormone, is not the functional opposite to the night-time melatonin, however. Serotonin is not the day to melatonin’s night, as it were. That position is held by cortisol. Like serotonin, cortisol production is also stimulated by exposure to bright light such as sunlight and is the primary hormone responsible for waking us up and getting us going in the morning. In the context of typical health and wellbeing discussions, chronically elevated cortisol is often viewed negatively due to the association with it being a primary stress hormone. But we do require a strong, well-timed cortisol rhythm, where cortisol rises sharply from early in the morning (just prior to sunrise), peaks around mid-morning following bright sunlight exposure (while melatonin is low), then drops away over the remainder of the day and into the evening (as melatonin begins to rise once again).
Even dopamine, the neurotransmitter responsible for, among other things, motivating us to get out and get stuff done, is made in conjunction with bright light exposure.
So, you can hopefully see the potential problems here. We spend a lot of time indoors. Too much time. It may also be dark when you go to work and dark when you come home. The very low levels of bright blue spectrum light we experience during the day is seeing our feel good and motivation biochemistry tank. With insufficient amounts of cortisol, serotonin, and dopamine in circulation, we’ll feel tired, fatigued, lethargic, apathetic, anxious, depressed… Sound familiar?
At night, the light intensity outdoors is generally well under 10 lux and mostly under 1 lux, even with bright moonlight. Meanwhile, indoors, with all the LEDs burning bright (modern household lights, electronic device screens, etc), it can be 200-300 lux in some rooms. During the day, this light intensity, relative to the outdoors, is very dark. But now, at night, 200 lux is 200 times brighter than 1 lux. Now this isn’t to say we should be sitting in the dark, huddled around candles, but it illustrates the light inversion we have in our modern world – our days are relatively dark, while our nights are relatively bright. This is undeniably messing with our heads, quite literally.
Recent research has suggested that spending too much time in relatively low light rooms could be changing the way our brains process information and impairing the growth of new neural connections. “Are Dim Lights Making Us Dimmer?”, read the headline of one report I reviewed. Our increasingly indoor lifestyles are also thought to be behind the global short-sightedness (myopia) epidemic, where up to half of young adults in the United States and Europe, and up to 90% of Asian teenagers are affected – over double the prevalence of 50 years ago. The strongest environmental risk factor for this large-scale loss of visual acuity across our populations of teenagers and young adults – the lack of bright natural light exposure associated with being indoors most of the day.
Many readers might be aware of, and perhaps even experienced, the phenomenon known commonly as the winter blues (Seasonal Affective Disorder – SAD). There seems a clear link between light exposure and a change in our mood, outlook, and wellbeing. A decline in serotonin levels with the reduced light exposure (length and intensity) and a concomitant increase in daytime melatonin levels, often in conjunction with dietary factors such as an insufficient specific amino acid intake, is at the heart of the winter blues we can often feel ourselves slip into. Living far from the equator appears to be a key risk factor for experiencing seasonal affective disorders, adding further support to the suggestion that changes in natural light exposures are fuelling this phenomenon.
The symptoms of winter-onset SAD include low energy levels, tiredness, cravings for foods high in carbohydrate (driving increases in body fat), sleeping problems, difficulty in concentrating, feelings of hopelessness or worthlessness, and suicide ideation. Summer individuals can experience a summer variant of seasonal affective disorder, but rather than depression, summer-onset SAD, driven by excessive light exposure (such as might be experienced during the “white nights” of high latitude countries in the summer months), is more likely to be characterized by anxiety and mania – easily over-stimulated, hyperactive, and displaying obsessive-compulsive type tendencies.
These extremes give us insight into the effects of light – too little, too much, poorly timed – on our mood and behaviour. While both winter- and summer-onset SAD may represent extremes, most of us function and experience variances in our moods along a continuum of light exposures. It’s hard not to see that rates of depression and anxiety are increasing while our light and dark exposure patterns are perhaps at their most extreme they’ve ever been in human history.
Like many of the common biological and evolutionary mismatches, the types of light exposures we experience now are relatively novel to us and our biochemistry. Electric lighting, on an evolutionary scale, is new enough. But as soon as you start considering urban life, work hours, LED lights, and our screen exposures, we are now considering something so very new to us and our delicately balanced brain chemistry. We have, in no uncertain terms, disconnected ourselves from the light and dark cycles of the planet. We cannot expect to do this without consequence.
It is at this point, as I wrap up, that we think about the practical solutions to dealing with this.
The first thing for most people, as always, is awareness. I encourage people to install a light meter app on their phones (given most phones have cameras, they already have a light meter installed – a simple app, such as Lux Meter, will allow access to this tool). Once you have this, you can begin to map your world, as it were.
Take some readings in the places you hang out. At your desk. If it is too dark, see if you can get one closer to a window. At your coffee shop. If too dark, find another, or better still, sit outside. Look for ways to get your eyes out into the bright light as often as you practically can, from as early in the day as you practically can. Get away from buildings and walk more in the open if possible. Don’t wear sunglasses first thing in the morning – it will feel bright at first (possibly a sign that your melatonin levels are still too high), but you will quickly adjust. An important piece of research I found as part of this project, suggested that it is our daytime bright light exposure which is more important for setting our melatonin pulse at night than avoiding blue light at night, with the bright light exposure during the day mitigating most of the blue light at night effect. That said, still use the light meter to measure your light exposure at night and take steps to darken your night as much as possible.
There is a lot of focus on sleep, diet, and exercise in the wellness space – and for good reason. But a key fundamental we are all missing is our light exposure patterns and the impact these have on our ability to sleep, eat well, and be motivated and energised enough to exercise. We need to take back the light, pushing back against the insidious daylight robbery we’ve all been exposed to.
For more reading on this subject, I can thoroughly recommend the book Chasing the Sun by Linda Geddes.