Happiness from the sun: how sunlight affects our mood and is even able to make us smarter

After having written about the negative impact of modern sunscreen on our health, I felt the urge to write on the benefits of sunlight once more, especially given the fact that summer is nearing its end. Melancholy sets in and there's an urge to not let this stop enjoying the sunlight as much as possible.
It can't be that I'm the only one feeling this urge so strongly, which is proof enough how sunlight influences our mood.

To my surprise, sunlight doesn't just influence our mood but can make us smarter, too!

How sunlight affects your mood

Sunlight has a profound impact on your mental health — more so than any other weather phenomenon. That's the conclusion of a study looking at links between weather and depression.

Mental health data from more than 16,000 students resulted in the conclusion how from nineteen different environmental factors among which the amount of sunlight, cloud cover, rain, wind chill, barometric pressure and smog , the only factor that really mattered was the amount of time between sunrise and sunset.
None of the other environmental factors had any significant association with emotional distress — provided there was enough sunlight.
The link remained even after controlling for factors such as season, body mass index, race, diet, exercise and time spent outdoors.


This shouldn't be a surprise, since so many people suffer from depression and fatigue in late autumn and winter which magically disappears in spring.

A deficiency of the vital nutrient of vitamin D, which can be counteracted with vitamin D3 supplements, is strongly associated with a higher risk of depression.
For example, research has shown having a low vitamin D level can raise your risk for depression by as much as 85 percent, compared to having a normal vitamin D level.
Fortunately, vitamin D supplementation can help alleviate symptoms of depression.

Sun exposure affects health in many ways besides vitamin D

When we talk about sun exposure to optimize vitamin D production, we're really only looking at a small portion of the action spectrum of light, because ultraviolet B radiation is the only portion able to photosynthesize vitamin D in your skin.

But the health effects and benefits of sunlight are not restricted to ultraviolet B. The composition of the different parts of the light spectrum are of crucial importance to achieve all of the benefits you can get from the sun.

Humans are adapted to sunlight as a complex stimulus, and when you remove that stimulus (sunlight), you end up with a variety of problems.
Sunlight induces coordinated endocrine adaptation effects. It affects sympathetic and parasympathetic activity, and is a major circadian and seasonal stimulus for the body clock. Our system, via the eyes and via the skin, detects the colors of the light in the environment in order to adapt the hormonal system to the specific needs of the time and place."

A large number of molecules (chromophores) found in the different layers of your skin absorb and interact with ultraviolet rays, producing a number of complex and synergistic effects.

There are additional chromophores in your mitochondria electron transport chain that respond to near infrared. This complex stimulus of sunlight affects not only your physical health by preventing diseases, it also impacts your mood and mental health. For example:

• Your body uses the near-infrared light spectrum to produce mitochondrial energy and maintain systemic equilibrium.
  Near-infrared also primes the cells in your retina for repair and regeneration, which explains why light-emitting diode (LED) lighting — which is devoid of infrared — is so harmful for your eyes.
  Now, if near-infrared plays such an important role in your body's energy production, it seems reasonable to conclude that if you're running low on adenosine triphosphate (ATP) — cellular energy — due to insufficient amounts of sunlight exposure, you'd start feeling sluggish and tired, and possibly depressed.
• Sunlight also regulates your circadian rhythm, and light therapy has been shown to be effective against depression, both SAD and non-seasonal major depression.
  When it's dark, your melatonin levels increase, which is why you may feel tired when the sun starts to set. In the heart of winter, this may be at as early as 4pm.
• Ultraviolet (UV) light also stimulates epidermal cells known as keratinocytes to make beta-endorphins, which have a mood-boosting effect.
• Serotonin is also released in response to sunlight, which helps elevate your mood and energy.
• UVA generates nitric oxide (NO) in your skin, which influences your body in a number of beneficial ways. It stimulates up to 60 percent of your blood to flow to your skin capillaries where they absorb this energy and infrared radiation.
  The UVA actually helps kill any infections in your blood while the infrared recharges your cellular battery.
  NO also protects your heart by relaxing your blood vessels and lowering your blood pressure, stimulates your brain and acts as a natural antioxidant. By lowering inflammation, it could have a beneficial impact on your mental health, as depression is strongly linked to chronic, low-grade inflammation.
  Part of why vitamin D appears to improve depression relates to the fact that it's a potent anti-inflammatory.

Can light exposure make us smarter?

Now onto the question whether light exposure can really make us smarter?
There's not yet much research which has been done on humans, but researchers from Belgium sought out the answer to this.

In a study they investigated how light exposure affects cognitive function in humans.

"The study is described by the editors as of fundamental importance, and represents a key advancement to our understanding of how different levels of light affect human behavior."

Light affects the emotional and executive areas of your brain

For context, prior research conducted on animals established that light exposure affects many subcortical structures, which are the parts of your brain that play "a pivotal role in cognitive, affective and social functions in humans."
Now, the researchers are investigating if the same effects are seen in humans, making the study a first of its kind.

"Translating findings on how light exposure affects the brain in animal models to humans is a difficult process, as the later maturation of the cortex in human beings enables much more complex cognitive processing. In particular, the question of whether hypothalamus nuclei contribute to the stimulating impact of light on cognition is not established."

The effects of light on the hypothalamus

Mrs. Campbell and her team recruited 26 participants to complete two cognitive tasks designed to stimulate the emotional and executive areas of the hypothalamus while being subjected to varying levels of light intensity. They used MRI (magnetic resonance imaging) machines to monitor brain activity in real time and record the results.

The hypothalamus is responsible for managing the endocrine system. Essentially, it acts as a central station, receiving signals from other parts of your brain to release and inhibit hormones essential for maintaining life. These include the thyroid gland, adrenal gland and reproductive organs. The hypothalamus also helps regulate your appetite and temperature.

Inside the hypothalamus, which all mammals have, lies the center master clock – the suprachiasmatic nuclei (SCN). The SCN cannot function on its own but requires environmental stimuli to synchronize the body clock. This allows you to follow a pattern of wakefulness and sleep.

The hypothalamus is generally divided into two areas regions — anterior (front) and posterior (rear). The anterior region handles the production of hormones needed by the body, while the posterior region is where oxytocin and vasopressin are stored after being produced in the anterior region. Oxytocin and vasopressin are hormones that perform crucial functions such as maintaining mood and regulating temperature.

Light intensities can have varying effects on different parts of the hypothalamus

The participants were asked to get an MRI scan one week before the trials began. They were also required to get around seven hours of sleep, and were prohibited from consuming caffeine and alcohol, as well as undergoing strenuous exercise.

To create the test environment, the researchers used a lightbox that illuminated a cable on both ends, allowing them to vary the intensity while the participants performed the tasks. The participants were then asked to complete two tests to identify the effects of light exposure on their cognition.

The two tasks were

1. Executive task — The participants were asked to determine if the current sound played to them was the same as one they heard two playbacks earlier, or if it contained the letter "K."
2. Emotional task — They were asked to determine the gender of a voice that used either a neutral tone or angry tone.

Throughout the study, the participants were alternatively placed in darkness or exposed to bursts of light exposure through four levels of illumination. 
Once results were recorded, the researchers noticed that higher light intensity increased activity in the posterior hypothalamus among the participants.

At the same time, higher light intensities resulted in decreased activity in the anterior and ventral sections of the hypothalamus. Furthermore, higher light intensities resulted in better performance in the executive task.

The role of the hypothalamus in your cognitive function

The study could not only help identify light’s effects on various brain structures but may also support further research into noninvasive treatments for sleep problems and cognitive fatigue.
The strength of evidence is compelling, supporting the authors’ analyses of the complex interplay between light exposure, hypothalamic activity, and cognitive function.

Their findings were supported by another study where it was noted that light exposure increases physiological arousal in the brain, leading to increased alertness.

The data from this specific study clearly illustrate that light exposure can have a profound effect on your cognitive performance. So, how can you take advantage of it?
Through a process called photobiomodulation (PBM).

How photobiomodulation can benefit your health

PBM refers to the process of using light therapy to benefit your health. Typically, this process involves using red and near-infrared wavelengths (with enough intensity) that your body can utilize.

One of the most notable benefits of near-infrared exposure is the increase in ATP (adenosine triphosphate) production in your mitochondria. Essentially, ATP is the energy currency used to power biological processes essential for life, such as muscle contractions, ion transport and chemical synthesis.

Earlier studies already noted how near-infrared exposure helped increase ATP in animal subjects and even reduced inflammation. Fruit flies exposed to near-infrared light also gained a significant increase in lifespan.

Another fantastic benefit of near-infrared exposure is melatonin production — 95% of melatonin is produced in your mitochondria in response to near-infrared light. The melatonin released by your pineal gland account for just 5% of the melatonin in your body.

Now, you might be wondering how mitochondria underscore these benefits. According to published research, your mitochondria play an important role in cognition. Here’s a succinct explanation, according to a 2023 study:

"Mitochondria have a crucial role in brain development and neurogenesis, both in embryonic and adult brains. Since the brain is the highest energy consuming organ, it is highly vulnerable to mitochondrial dysfunction. This has been implicated in a range of brain disorders including, neurodevelopmental conditions, psychiatric illnesses, and neurodegenerative diseases."

In another 2021 study, mitochondrial dysfunction has been implied to be a common mechanism involved in the most recognizable features of Alzheimer's disease.

Linking all points together, harnessing the power of PBM can help boost mitochondrial health. In turn, healthy mitochondria can help maintain optimal cognitive function.

Can home saunas provide the same benefits as PBM?

Electric saunas designed for your home typically emit far-infrared light, which can still provide detoxing benefits. However, with some tinkering, they can be modified to function as a PBM device as well, which can save money since you won’t need a dedicated PBM device.

You can modify your sauna by using incandescent heat bulbs that emit the majority of their energy as near-infrared light. While it may take some work, the effort will be worth it.

If you want to save time and energy, consider near-infrared bulbs with metal guards that prevent the glass from accidentally breaking and injuring you.

This simple trick can increase the benefits you experience in your sauna since you’re also getting the benefits of PBM from the new bulbs. Done correctly, eight incandescent red bulbs can heat up to 70°C in about 20 minutes, which is far better than typical far-infrared saunas.

It’s also good to test your sauna for electromagnetic field (EMF) radiation. If it does have EMFs, it is recommended to shield your sauna as best as you can to protect your health.

As for the actual sauna session, it’s always important to start out slowly. Listen to your body so you can decide how much heat stress you can tolerate. Ideally, sauna sessions should last anywhere between 15 and 30 minutes.
Also, remember to stay hydrated before, during and after, since you’ll be sweating a lot.

Sunlight is the ideal light source

While a PBM device (or a modified sauna) can be a fantastic addition to your health routine, you shouldn’t shun proper sun exposure. Ideally, spend more time outdoors whenever possible. Only use PBM devices to get red and near-infrared light you need if you cannot get enough regular sun exposure.

Humans need direct sun exposure in order to optimally thrive, and while artificial lighting sources offering specific light spectrums may be helpful for various problems, ideally, we need the full spectrum of light that natural sunlight offers.

If you’re going out to get sunlight, it is recommended to do it during solar noon. For those living in areas that implement Daylight Saving Time, it should be an hour later from 12:30 to 13:30 and possibly a bit later yet in the Netherlands as it is positioned at the western end of the time zone.
Scheduling your daily walk around this time allows you to maximize the benefits of ultraviolet B rays and near-infrared radiation from the sun.

Blocking blue light at night can help transform your sleep

Last but not least, light exposure during the day has a major impact on your sleep quality, which in turn affects health in countless ways. Getting bright light exposure first thing in the morning and mid-day helps properly "set" your circadian clock, while bright light from artificial lighting and screens in the evening prevents melatonin release, inhibiting sleep.

Normally, your brain starts progressively increasing the hormone melatonin around 9 or 10 pm, which makes you sleepy. Melatonin acts as a marker of your circadian phase or biological timing.

In a nutshell, this hormone influences what time of day or night your body thinks it is, regardless of what time the clock on the wall displays. Besides regulating your sleep cycle, it also provides other important health benefits, including helping to prevent cancer.

Somewhere between 50 and 1,000 lux is the activation range within which light will begin to suppress melatonin production. However, wavelength is also important. Red and amber lights will not suppress melatonin while blue, green, and white lights will.

The reason for this is because these are the wavelengths are the most common outdoors during daytime hours. So, you’ll want to avoid the blue light wavelength after sunset. This includes artificial light, and light emitted by electronics such as your TV, computer, and other electronic screens.

The blue light range (400–490 nm) can also induce photoreceptor damage in your eyes, so besides disrupting your sleep this is another potential problem with light emitting screens.
As noted in one recent study "it is important to consider the spectral output of LED-based light sources to minimize the danger that may be associated with blue light exposure."

Conclusion

Sunlight can impact both mood and cognition. Sunlight not only alleviates depression and regulates circadian rhythms but also boosts serotonin, nitric oxide, and vitamin D production.
These effects improve physical and mental health, including energy levels and immune function.
Moreover, light therapy or exposure to specific light spectrums, like near-infrared, can increase cognitive function and mitochondrial efficiency.
While photobiomodulation (PBM) can be of great significance, sunlight remains the ideal natural light source to promote overall well-being and sleep quality.