Here’s how pitch black slumber benefits health.
Maybe you’ve seen it: A small but significant research study recently impressed health experts and popped up in lots of news outlets. In mid-March, the Proceedings of the National Academy of Sciences published a study showing that people who sleep with even just some light in their surroundings can experience serious health impacts. According to the abstract, “This laboratory study shows that, in healthy adults, one night of moderate (100 lux) light exposure during sleep increases nighttime heart rate, decreases heart rate variability, and increases next-morning insulin resistance when compared to sleep in a dimly lit (less than 3 lux) environment.”
Although the study, which was conducted at Northwestern University, included only 20 participants, the findings are important and will no doubt be sussed out even further via more research. In the meantime, they warrant our attention. Why? Bottom line—It seems that light can interfere enough, over the course of even just ONE night, to measurably increase insulin resistance and heart rate. To boot, researchers mentioned that subjects who reported feeling well rested nonetheless also experienced these side effects. In other words, waking with a sense of wellbeing doesn’t mean your health has not been affected.
How much light is too much? It may be tricky to estimate. The Northwestern study compared two groups. One slept in moderate light of 100 lux, which according to researchers (in an NPR article), is just enough to navigate a dim room but not enough to read by. The other group slept in an environment of extremely low light (3 lux), which is VERY dark. (For example, the light of the full moon is approximated at about half a lux. Personally, I’ve been roused at 4am when that amount has made its way through the gap between the blinds and the wall.) It’s probably safe to say that a TV will definitely generate too much light but a red nightlight might make an okay choice.
In addition to this research, studies have pointed to other alarming impacts of light during sleep on health. A study published in 2017 in the American Journal of Epidemiology reported a link between bedtime light and depression. Assessing 863 subjects in Japan, it revealed that those who slept in a room illuminated by more than 5 lux (again, quite dim) exhibited a significantly higher depression risk over approximately 24 months. Another study of more than 40,000 women (published in 2019 in JAMA) found that sleeping with a TV or light on was associated with a 17% increased risk of gaining 11 pounds over the course of five years.
Luckily, we can darken a bright room quite easily and inexpensively. For me, it required buying some (actually quite nice) blackout drapes and unplugging devices—two digital clocks and an unused TV (with a display resembling a cockpit). I’ll be honest: For the first minute, TOTAL DARKNESS struck me as astounding. My hubby and I had never really thought about the amount of light emanating from those seemingly innocuous electronic displays, from cell phones that occasionally popped aglow, and from lights on the street (not to mention the aforementioned moon which when full tracks right down our left window).
We have had to adjust, but just a bit. We do now need to use the faint light of our phones to find the bathroom at 3am, and I plan to install some dim tap lights at the base of our nightstands for such journeys. I also make good use of a bright-light emanating alarm clock to wake, since the room would remain totally cave-like all day if I didn’t open the drapes. (This I’ve been using for a while, actually, to stay on top of my circadian game during the past winter. It’s such a gentle way to wake up that it’s really worth switching if you're someone who doesn't need freight train level noise to reach consciousness.) But any “inconvenience” has completely faded now that we enjoy the treat of slumbering in delicious darkness. I’m definitely sleeping more deeply, and if the research holds, my health will benefit. It’s something I highly recommend exploring.
Photo by Daria Shevtsova on Pexels