Newsletter #217

Researchers at Northwestern recruited twenty healthy young adults and randomly assigned them to one of two different conditions. In one, participants spent two consecutive nights in a very dimly lit room, and in the other, they spent one night in a dimly lit room (less than 3 lux) and another in a moderately lit room (100 lux - this is considered bright enough to see where you’re going but not suitable for reading comfortably). Individuals who slept in the moderately lit room, unsurprisingly, had poorer sleep quality, spending less time in REM and restorative slow-wave sleep stages. They also showed decreased insulin sensitivity (-16% in the Matsuda Insulin Sensitivity Index). This change in metabolic function was linked to increased activity of the sympathetic nervous system, demonstrated by increased nighttime heart rate and decreased heart rate variability.

Researchers analyzed cardiovascular risk factors in a group of 552 older adults (63-84). They equipped the participants with wrist-worn actigraphs for one week to objectively measure their sleep patterns and light exposure. Compared to those who slept in total darkness, subjects who slept with any light on in the background, even very dim light, were twice as likely to have diabetes. Their likelihood of having high blood pressure was increased by 74%, and the likelihood of being obese was increased by 82%.

Researchers in North Carolina analyzed data from 43722 women located all over the United States, who did not have a history of cancer or cardiovascular disease at the start of the study, and who had normal sleep patterns (no shift work). After about six years of followup, exposure to artificial light at night was found to be associated with greater likelihood of going on to gain significant amounts of weight over the course of the study, even after adjusting for measures of sleep duration, diet, and physical activity. Furthermore, women who slept with a television or light on in their room were 22% more likely to be overweight and 33% more likely to be obese, compared to women who slept in total darkness.

Back in the 1960s, a biologist named Lars Wilsson wanted to understand where beavers’ dam-building skills originated. Were they innate, or learned from adult beavers? To untangle this mystery, he started raising some baby beavers away from their families. When he would release them in close proximity to running water, they would try to construct dams, despite a lack of training from their parents. Sure enough, dam-building is a natural behavior in these critters.

But Wilsson happened to notice that the beavers didn’t engage in dam-building when they were presented with still water. To figure out what stimuli might trigger this behavior, he started placing speakers in the area and playing the sound of running water over rocks. The beavers would start to try to stack mud and sticks over the speakers!

This quirk has actually been exploited by humans - to the benefit of beavers. Beavers’ dams occasionally cause streams to overflow their banks, resulting in property damage. But rather than destroy the dams or harm the beavers, people can install outflow pipes through the dams, outfitted with noise-dampening filters. Unable to hear the flowing water, beavers will not intervene.

Glycine may do other good stuff too - for instance, a recent rodent study showed that glycine supplementation extended lifespan. Studies typically use around three grams, which you can easily add to your beverage of choice right before bed. It tastes sweet (hence the name), so it’s not too hard to take.

This week, we’d like to highlight our How-to Guide for Smart Daily Light. We evolved in the presence of natural daily cycles of light and darkness. But obviously, the invention of artificial lighting means that we can now fully control when and how much light we’re exposed to, which has altered this relationship. Today, most of us spend the majority of the day indoors, under comparatively dim artificial lights. Then, after sundown, we are exposed to more bright light, and importantly more blue light due to our digital devices. Consequently, we are getting less bright light during the day and less darkness at night.

This is important because light sends crucial signals to the body, and the intensity and timing of this light matters for your health as well as your performance. But fortunately, there is a lot you can do about it. In this guide, we discuss how you can achieve a pattern of natural light and darkness in the modern world by adjusting behavior, modifying your indoor spaces, configuring your devices, and more.

Thanks for reading, enjoy the weekend, and we'll see y'all next week!

https://mailchi.mp/humanos.me/newsletter-217