A study from Northwestern University Feinberg School of Medicine in Chicago explores the link between light exposures during sleep and health risks. The research serves as a warning for the many people living in industrialized nations where light tends to be omnipresent.
Sleeping while exposed to any type of light whatsoever — even dim light — is linked to an increase in the likelihood of obesity, diabetes, and hypertension (high blood pressure) in older adults, the study finds.
Corresponding author for the study, Dr. Minjee Kim, of Northwestern Medicine Feinberg School of Medicine, said in a press release: “Whether it be from one’s smartphone, leaving a TV on overnight, or light pollution in a big city, we live among an abundant number amount of artificial sources of light that are available 24 hours of a day.”
“It appears that even a tiny amount of light has a noticeable effect on our body’s response,” Dr. Kim told Medical News Today.
“Previous animal and some human studies have suggested a potential association between mistimed light — not enough light during the day, too much light at night — and obesity,” said Dr. Kim.
“There was little data on light exposure patterns in older adults,” said Dr. Kim. “Since older adults are already at increased risk of cardiovascular diseases, we wanted to know how frequently older adults are exposed to ‘light at night’ [or “LAN”], and whether light at night is correlated with CVD risk factors.”
It is not only older people whose health may be affected by not sleeping in deep darkness.
“In a previous study done by our group, even one night of dim light exposure during sleep raised heart rate and blood glucose in young, healthy adults who were brought into a sleep lab for an overnight experiment,” Dr. Kim explained.
Dr. Jonathan Cedernaes, a sleep expert from Uppsala University in Sweden, who was not involved in either study, told MNT:
“The fact that this is observed in older people may represent the more cumulative effects of such a mechanistic relationship, meaning that the adverse cardiometabolic effects of nighttime light exposure may become more evident over time (meaning in more advanced age, if one maintains such a lifestyle or exposure pattern over years to decades).”
The study was published in the journal Oxford Academic SLEEP.
A real-world study
Unlike the group’s previous research, the new study observed the real-world effects of LAN, tracking the sleep of 552 older men and women.
“In the current study, we measured light exposure and sleep in older adults (ages 63-84) for seven days using a wrist-worn device. Instead of bringing these older adults to the sleep lab, we collected data in their routine environments,” said Dr. Kim.
They found that less than half of these older adults slept in a pitch-black room for at least five hours.
“We were frankly surprised to find out that more than half of the older adults were sleeping with some light at night,“ Dr. Kim said. “Adults who slept with some light during their sleep period were generally exposed to dim light.”
The researchers found that the likelihood of developing high blood pressure (hypertension) was increased by 74%, obesity by 82%, and diabetes by 100%. Participants were also tested for an increased risk of hypercholesterolemia, but no difference was observed.
The study lists three possible mechanisms behind light’s disruptive effect during sleep:
- Light is the main synchronizer of the body’s circadian rhythm or clock. Light during sleep may disrupt this rhythm and thus any clock-related physiological processes.
- The pineal gland produces and secretes melatonin, the “hormone of darkness,” during dark periods. Light may reduce melatonin’s metabolic and circulatory function with its anti-oxidant, anti-inflammatory, and vasodilatory properties. Lower melatonin levels correlate with an increased risk of diabetes in women and an increased risk of hypertension in young women.
- Light may trigger the autonomic nervous system’sTrusted Source sympathetic arm. During healthy sleep, the system responsible for fight or flight responses relaxes, slowing the body’s heart rate and respiration in a parasympathetic state.
When asked if more light equals a higher risk of disease, Dr. Kim replied, “We found a trend towards a stronger association — a higher rate of obesity and diabetes — with more light exposure at night. We hope to confirm this finding with future studies across a broader age range.”
Sleeping for better health
“While we cannot conclude anything beyond association because of the cross-sectional (‘snapshot’) nature of the study, I encourage everyone to try to avoid or minimize any light at night if possible,” Dr. Kim advised.
“It may be as simple as not using electronic devices near the sleeping place and blocking light with a sleeping mask,” he added.
Still, Dr. Kim cautioned: “If people need to use a night light for safety, they should try to keep it as close to the ground as possible to minimize light entry to the eyes. If they need to use the bathroom at night, and it is dangerous to walk in complete darkness, try to use dim light for the shortest necessary period.”
It also appears that the color of light in which a person sleeps matters.
“I would recommend using amber or red light for [a] night light over blue light. Amber/red light (longer wavelengths) is less disruptive to our circadian clock in the body than lights with shorter wavelengths such as blue light,” Dr. Kim explained.
“Certain groups are forced to work at night,” added Dr. Cedernaes, and must sleep in the day. “There are also ways to block light (e.g., specific filters in glasses), and more studies may be warranted to establish methods to counteract light exposure… [and] reduce cardiometabolic risks.”