That soft, comforting glow from the nightlight is causing more trouble than it’s worth.
In February, we reported on a study that found that even the dimmest nightlight causes the sleep-inducing hormone melatonin to plummet in children, keeping them wide awake.
In March, we reported on a Northwestern University Feinberg School of Medicine study that when healthy young adults slept with “moderate overhead light”—about the equivalent of a day under heavy black clouds or a TV—an increased heart rate during sleeping and disturbed glucose metabolism the next morning.
But one night
In other words, increased risk factors for developing heart disease and diabetes resulted from sleeping one night with dim lights.
“The results of this study show that just a single night of exposure to moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, diabetes, and metabolic syndrome,” said senior study author Dr. Phyllis Zee, chief of sleep medicine at Northwestern.
“It’s important for people to avoid or minimize the amount of light exposure during sleep.”
Elderly at increased risk in a new study
dr. Zee has contributed to a new study focusing on seniors already at higher risk for diabetes and cardiovascular disease.
She hypothesized that exposure to ‘light at night’ (LAN) in the elderly is associated with a higher prevalence of individual risk factors for cardiovascular disease.
Dr. Minjee Kim, the corresponding author of the new paper and assistant professor of neurology at Northwestern, explains, “Whether it’s from your smartphone, leaving a TV on at night, or light pollution in a big city, we live between an abundant number of artificial light sources available 24 hours a day.
Multiple sources of artificial light can disrupt our sleep. Photo: Getty
“Older adults are already at higher risk for diabetes and cardiovascular disease, so we wanted to see if there was a difference in frequency of these diseases associated with light exposure at night.”
How the study worked
This was a real-world study, not conducted in a sleep lab.
More than 550 participants were recruited: men and women aged 63 to 84.
For seven days and nights, they each wore an actigraph, a device like a wristwatch that measures sleep cycles, average movement, and light exposure.
Less than half of the participants “had five hours of complete darkness per day”.
The rest of the participants “were exposed to some light even during their darkest five-hour periods of the day, which were usually in the middle of their sleep at night.”
Those exposed to any amount of light at night “were significantly more likely to have obesity, high blood pressure, and diabetes compared to adults who were not exposed to light at night.”
This was a cross-sectional study, meaning the researchers don’t know “whether obesity, diabetes, and hypertension make people sleep with a light on, or whether the light contributed to the development of these conditions.”
They suggest that individuals with these conditions “might be more likely to use the bathroom in the middle of the night (with the light on) or have some other reason for keeping the light on.”
For example, someone with numb feet due to diabetes may want to keep a nightlight on to reduce the risk of falling.
A possible biological mechanism
There is an abundance of evidence dating back years that has found a strong link between poor sleep and an increased risk of obesity and type 2 diabetes.
It may be that turning on a light at night promotes poor sleep. To some extent, this is undoubtedly true.
But looking at the clinical research done with children and young adults (the studies mentioned at the beginning of this report), it probably isn’t the whole story.
It makes sense – we know that light is like a switching mechanism for the body’s circadian rhythms that regulate not only when we feel tired or awake and when it is day and night but also a host of metabolic functions.
The circadian clock regulates when we’re hungry, when we respond best to exercise, and where our body temperature stays throughout the day. Ase d, Kim noted: There may be a biological explanation beyond disturbed sleep, linking slightly to an increased risk of obesity, diabetes, and high blood pressure.
“It’s not natural to see those lights at night,” she said.
She said the circadian signal is weakened, and over time “that affects our health.”