Newsletter #180: Sunlight + Your Mind 🌞
Good morning humanOS friends, hope y’all are having a delightful weekend so far!
Since the days are getting shorter and shorter, and the end of Daylight Saving Time in the US is looming just a few weeks away, we decided to take a look at some recent studies examining the effect of outdoor light on the mind.
The human body is exquisitely sensitive to the external cues of sunlight, in ways that we are only just now beginning to fully understand and appreciate. For instance, recent research has revealed that fat tissue has receptors for sunlight, which may influence our metabolism, and animal experiments suggest that regular exposure to solar radiation affects body fatness and cardiovascular disease.
And we also know that ambient light affects the mind. A Northwestern study from a few years ago found that employees who worked in offices with windows reported better quality and life and more physical activity, compared to counterparts in windowless work environments.
There are a couple reasons why this might be the case. It may be due to better sleep - the subjects who worked in offices with lots of daylight got 46 minutes more sleep on average - which would certainly make people more perky. We also know that bright light, especially blue-enriched light, tends to improve alertness and mood. Of course, the timing is pretty important, since you don’t really want to experience that alerting effect late at night.
This Week’s Research Highlights
☺️ Outdoor light exposure is associated with improved mood and sleep parameters.
Researchers analyzed data on daytime light exposure and various outcomes related to mood and sleep from a large cohort of adults in the UK (n = 502,000). They found that each additional hour spent outdoors during the day was associated with lower odds of lifetime depression, antidepressant usage, less frequent anhedonia and low mood, greater happiness, and lower neuroticism, independent of demographic, lifestyle, and employment status. Unsurprisingly, daylight seemed to improve sleep and circadian outcomes as well. Each additional hour of daylight was linked to greater ease in getting up in the morning, less frequent tiredness, fewer insomnia symptoms, and earlier chronotype.
☀️ Exposure to sunlight may enhance learning and memory by increasing glutamate in the brain.
It has been known for some time that exposure to ultraviolet light elevated blood levels of a molecule known as urocanic acid. But the biological significance of this substance was largely unknown. To gain some insight into its purpose, researchers shaved mice and administered ultraviolet light to the exposed skin for two hour sessions.
They found that serum urocanic acid levels rose, as expected, and that they also entered the central nervous system - levels of the molecule were about 2-fold higher in the rodents’ cerebrospinal fluid, and markedly higher in various regions of the brain. This is important because urocanic acid appears to play a role in the conversion of the amino acid histidine into glutamate, the most abundant neurotransmitter in our nervous system. And indeed, this UV-mediated increase in urocanic acid promoted glutamate production in the brain.
Okay, here is the practical significance of this finding: the researchers then had the mice perform a series of tasks that test motor learning and recognition memory, including this scary-looking task. The mice that had been exposed to the UV light and exhibited higher urocanic acid were much better at cultivating the balance and coordination to master this test, as well as others. Of course, more research is needed to figure out whether and to what degree this might apply to humans, but it’s a pretty cool finding!
🪟 Using “smart windows” to increase daylight inside homes boosts circadian alignment, sleep, and mental health.
Researchers had twenty participants spend one week in their apartments with standard windows with blinds, and another week while their apartment windows were equipped with special electrochromic glass, which tints dynamically in response to the location of the sun and helps filter solar light more efficiently (meaning more sunlight is getting into the residences than they normally would, and the light that penetrates is tilted more toward shorter wavelengths). Participants wore sleep-tracking devices over the course of the study, and filled out questionnaires on their mental health. During the week when the subjects were surrounded by the electrochromic glass, they fell asleep 22 minutes sooner and experienced greater sleep regularity. Furthermore, their psychological surveys revealed an 11% reduction in anxiety levels and a 9% decrease in stress levels. This is a nice example of how advances in technology can, ironically, counteract some of the negative health effects of modern lifestyles.
Random Trivia Question of the Week
🤔 Why do giraffes have blue tongues?
🦒 ANSWER
Podcasts We Loved This Week
- Mario Kratz: Is eating full-fat dairy, low-fat dairy, or no dairy better for cardiometabolic health? Via Sigma Nutrition.
- Clifford Nass: The myth of multitasking. Via Science Friday.
Products We Are Enjoying
Alaska Northern Lights Northstar Light Therapy Lamp
If you’re not able to get outside (or if the sun isn’t cooperating with your schedule), the next best thing is probably a light box, which is designed to mimic the uniquely bright and intense light emitted by the big globe in the sky. This is especially important if you struggle with circadian rhythm alignment during the colder months or if you suffer from seasonal affective disorder. But not all of these lamps are created equal. Experts say that good light boxes need to have a large light surface, with a brightness level of 10,000 lux, and surprisingly few on the market actually meet this criteria.
Researchers at the Yale School of Medicine compared samples of various lightboxes, and this was one that met their specifications. It is pretty big and pricey, but if you battle winter blues or just want to improve your circadian alignment, it’s probably worth it, especially if you are someone (like me) who hasn’t seen benefits from the smaller cheaper models.
humanOS Catalog Feature of the Week
Thank you so much, as always, for reading, and see y'all next week!