In This Article
Circadian Rhythm Disruption and Light
By now, most everyone has heard that checking your phone before bed and exposure to blue light will block the sleep hormone melatonin.
Current research now tells us that even a bit of dim light at night, from a television or nightlight, can also have consequences, creating health concerns well beyond sleep.
In a nutshell, any exposure to light at night will disrupt your circadian rhythms, which means that the biological clocks in your cells are unable to stay in sync with the light dark cycles created by the motion of our planet.
New studies have linked dim light exposure at night to cardiovascular concerns, diabetes, obesity, stress, anxiety, and much more.
Such disruption is more common than you think, with studies reporting that 40 percent of the population sleep either with a bedside lamp or bedroom light on or with the TV on. In this article, let’s explore the top ten health concerns with nighttime light exposure.
10 Health Risks Associated Using Lights at Night
1. Blood Sugar Imbalance
Emerging evidence from a study out of Northwestern University indicates that light exposure plays a role in human metabolic regulation, with evening light linked to blood sugar concerns, including decreased glucose tolerance and decreased insulin sensitivity. The researchers found that while blue light had the most dramatic health effects, even dim light could alter healthy blood sugar levels. The researchers also reported that light exposure in the bedroom during sleep was associated with a higher incidence of type 2 diabetes in the elderly.
2. Cardiometabolic Health Risks
Cardiometabolic health concerns encompass a series of medical issues, including insulin resistance, metabolic syndrome (high blood sugar, high blood pressure, abdominal fat, high triglycerides, low HDL cholesterol), pre-diabetes, cardiovascular disease (CVD), and type 2 diabetes. In this study, the group that was exposed to more light at night was more likely to have insulin resistance, metabolic syndrome, and diabetes.
3. Higher Stress
The Northwestern University study also found that exposure to light at night increased heart rate, which is a measure of increased sympathetic stress (fight or flight response). Light exposure at night also lowered heart rate variability—a measure of parasympathetic activation (rest and digest response). These findings were confirmed by finding higher levels of cortisol production in the group that was exposed to light at nights. Higher sympathetic stress at night can be a precursor to insulin resistance and pre-diabetes and the development of obesity and metabolic syndrome. Ideally, you should have greater levels of parasympathetic activity at night in order to rejuvenate and prepare for the next day. To accomplish this, your sleep has to uninterrupted, by noise, light, and more.
4. Obesity Risk
In the same study, researchers found that a small nightlight, or a light from an outside room or a television was associated with obesity in women. Researchers concluded that the incidence of obesity was highest in those who reported sleeping with a television or light on in their bedrooms.
5. Higher Anxiety Levels
There is no shortage of studies that have linked artificial light at night to mood and anxiety. In one study of more than 10,000 adolescents, the group that was exposed to the most light at night went to bed later and suffered from higher rates of anxiety than the group that was exposed to the least amount of light at night.
In a report that reviewed 12 studies on more than 700 patients, melatonin was compared to a standard western medication for pre-surgical anxiety. The researchers concluded that melatonin may be as effective for occasional presurgical anxiety that the standard western treatment. Finally, in a meta-analysis of 13 studies, there was evidence for associations between screen time and mental and physical health concerns.
6. Reduced Sleep Quality
Reported in the Northwestern study as well as other studies, nighttime light exposure, either from outdoor or indoor sources, has negative impacts on subjective and objective sleep quality as measured by reduced total sleep time, sleep efficiency, sleep latency (time getting to sleep), and increased wake ups or arousal after sleep onset, plus reduced slow wave sleep. There is no organ or organ system in the body that is not affected by disturbed sleep.
7. Lower Melatonin Levels
Exposure to light at night form indoors or outdoors has been linked to lower melatonin production and circadian disruption. Research has linked lower melatonin to increased incidence of diabetes and insulin resistance. The effect of light at night and lower melatonin production on the body’s circadian rhythms has been linked to heart, neurodegenerative, psychiatric, and sleep concerns. Since melatonin governs the timing of the body’s biological clocks in every organ, the negative impact of melatonin-induced circadian disruption is hard to quantify or overestimate.
8. Breast Health
Numerous studies in Israel, Korea, and around the world have found higher incidence of breast cancer in populations that are exposed to greater levels of outdoor ambient light at night. The studies looked at the earth with satellite photography and determined urban areas had greater light at night had higher rates of breast cancer. These risk factors are easily mitigated with blackout curtains which have become more popular of late for urban dwellers.
9. Mitigate the Effects of Aging
In numerous animal studies, disruption of the body’s circadian rhythms and exposure to light at night have been linked to shorter lifespans. Early death due to circadian disruption has been linked to an increased risk of cancer, heart disease, diabetes neurodegeneration, and cognitive decline.
In one study even the oceans coral reefs were dying at a faster rate when exposed to light at night. In another study in French Polynesia, chronic light exposure at night reduced the growth of the fish on the coral reefs by 44 percent and shortened their lifespans by 36 percent. We are all circadian beings and ignoring this fact is at our own peril.
10. Cognitive Decline
The effect of chronic light exposure at night has been linked to accelerated cognitive decline. In a study [link] with mice, dim light at night increased oxidative stress in the brain and reduced the natural production of the brain’s antioxidants, including superoxides dismutase and catalase. The brain-derived neurotrophic factor (BDNF) protein that rebuilds brains cells was also blocked with light exposure at night. Interestingly, this study shows that taking a dose of turmeric (curcumin) was able to mitigate the negative impact of light exposure at night.
In a 2021 study on more than 20,000 people, researchers found that those who got less sleep from circadian disruption had higher rates of cognitive decline. Another study found that poor sleep affects the flow of the brain’s cerebral spinal fluid, which acts as a brain washing fluid while we sleep. This affects the brain’s ability to detoxify the more than three pounds of plaque and toxic material from the brain associated with cognitive decline.
6 Tips to Avoid Light at Night
- Start dimming lights in the early evening.
- Wear blue light blocking glasses or use the blue light filter on all your screens at night.
- Avoid turning lights on in the bedroom. If you need a nightlight, use an amber colored light and place it closer to the floor.
- Use blackout shades to block outdoor ambient light or an eye mask while sleeping.
- Tape off LED indicator lights on the computers and technology in the bedroom.
- Mitigate circadian stress with Low-Dose Melatonin supplementation. Studies have shown that micro dosing melatonin is as effective as higher dosages without the body building a tolerance.