Light and Sleep

Woman sleeping in the sun

Light and Sleep 



How often do you fall asleep with the lights (or a light source of some source) still on? You might have fallen asleep watching TV, forgotten to turn off the lights because you were too tired, or dozed off while working on your laptop. No matter the reason, you are not alone, as it is estimated that nearly half of all adults sleep with some kind of light on. 

Sleeping with the lights on is a bad habit that you should break sooner rather than later. Here are five reasons why you should not sleep with the lights on. 


It causes hormonal imbalance. 

At night, the pineal gland (epiphysis cerebri)—an endocrine gland in your brain-produces a hormone called melatonin. Melatonin is important because it regulates as well as synchronizes your body’s circadian rhythm, which is more commonly known as your normal sleep-wake cycle. This hormone is also responsible for other vital bodily functions such as blood pressure regulation, reproduction, and preventing inflammation. However, research has shown that sleeping with the light on disrupts the body’s melatonin production. Dr. Joshua Gooley of Brigham and Women’s Hospital and Harvard Medical School studied 116 volunteers, aged 18 to 30, and exposed them to room light and dim light for eight hours before sleeping for five consecutive days. Results showed that exposure light shortened the production of melatonin by an average of 90 minutes (about 1 and a half hours). It also revealed that light exposure while sleeping cuts off melatonin by more than 50 per cent. 

Sleeping with a light on can play havoc with insulin levels and consequently impair the response to glucose, a sleep-lab study indicates. 

"The most important finding" is that compared to one night in a dim light environment, "one night of exposure to a moderate level of room light while sleeping with eyes closed increased heart rate and nervous system activity during the entire sleep period," said senior author Phyllis C. Zee, MD, PhD.  

And on the morning following the moderate room light condition, a higher amount of insulin secretion was required to normalize glucose levels following ingestion of a bolus of glucose in an oral glucose tolerance test, consistent with higher insulin resistance according to Zee.   

The study by Ivy C. Mason, PhD, also of Northwestern University, and colleagues was published in the Proceedings of the National Academy of Sciences 

Melatonin levels were similar under the two light conditions, Zee added, which "suggests that the effect of light during sleep on these cardiometabolic measures were more likely due to activation of the sympathetic [nervous] system and less likely due to changes in sleep or suppression of melatonin by light.’’ 

"Attention to avoiding exposure to light at night during sleep may be beneficial for cardiometabolic health," the researchers conclude.


It increases blood pressure. 

Since melatonin also regulates your blood pressure, the decrease in melatonin caused by unnecessary exposure to light during sleep time can raise your blood pressure. 

Research conducted by Chronobiology International determined that people who were exposed to excessive amounts of light at night had significantly higher blood pressure than people who slept in the dark. 


It triggers migraines. 

Do you like using gadgets before sleeping or watching TV in bed? If so, you should stop it immediately. Electronics such as smartphones, laptops, tablets, and televisions emit blue light that can trigger migraines. Blue light causes oxidative stress, which in simple terms means your body’s ability to flush out toxins is severely hampered. This leads to migraines, eye strain, and in worst case scenarios, even blindness. 

Another thing that can make migraines worse is lack of sleep. As previously mentioned, being exposed to too much light at night interferes with your natural sleep-wake cycle, which makes you wake up earlier than you intended, thereby causing a bad headache. 


It increases the chance of insomnia. 

From everything that has been mentioned, there is no question that sleeping with the lights on has an adverse effect on your health. Over time, the issues that arise from exposure to light at night can snowball into sleep disorders such as insomnia. Here is how it can happen. When your body has low melatonin, your sleep quality suffers. You do not feel well-rested because you find yourself waking up in the middle of the night, not just once but numerous times. The lack of rest causes you to get migraines as soon as you wake up in the morning. Sooner or later, a pattern like this will develop into insomnia. 


It leads to depression. 

When you have not had a good sleep for quite a while, it is not only your physical state that suffers, but your mental state as well. Several studies have proven the direct correlation between insomnia and depression, and the worst part is that it is often a vicious cycle. When you have insomnia, you do not feel well emotionally, so you end up with depression. In turn, this depression makes it harder for you to fall asleep and worsens your already existing insomnia. 


Shift Work Disorder 

Some work schedules, known as shift work, require working into the evening or overnight. Night shifts may be an everyday part of a job or part of a rotating schedule. The Bureau of Labor and Statistics estimates that around 16% of workers in America have evening or overnight shifts. Shift workers typically have to sleep during the daytime, putting them at elevated risk of a misaligned circadian rhythm and the development of shift work disorder. This circadian rhythm disorder can cause insufficient sleep, excessive sleepiness at inopportune times, mood problems, and elevated risk of workplace accidents. 


Other Circadian Sleep-Wake Disorders 

Circadian rhythm disorders can happen when a person’s internal clock gets shifted too far forward or back or if it fails to follow a stable 24-hour schedule. These problems are frequently connected to a person’s daily behavior and light exposure. 

One treatment for many circadian disorders is light therapy. The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information which uses sitting close to a high-powered lamp at scheduled times to retrain the body’s internal clock. The strong lamp is meant to mimic daylight and is often used in the morning to normalize circadian timing. 


What Other Steps Can Improve Sleep and Circadian Rhythm? 

In addition, you can take steps to improve your sleep hygiene and reset your circadian rhythm. Avoiding excess caffeine, having a consistent sleep schedule, and getting regular exercise, are examples of how your habits and routines can support healthy sleep. 

If you have long-lasting sleeping problems that are affecting your energy, thinking, or mood, you should talk with us at Palmetto Endocrinology to help who can best determine the cause, including any potential circadian rhythm disorder. 

Joseph W. Mathews, MD, FACP, FACE, ECNU, CCD Joseph Mathews, MD, FACP, FACE, ECNU, CCD Joseph W. Mathews M.D., a board certified Endocrinologist and Medical Director of Palmetto Endocrinology, was born and raised in South Carolina. He earned his Bachelor of Science in Biology from the College of Charleston, Cum Laude. He then achieved his M.D. at the Medical University of South Carolina where he also completed his residency in Internal Medicine and a Fellowship in Endocrinology, Diabetes, and Metabolism. Dr. Mathews is also a Fellow of both the American College of Endocrinology and the American College of Physicians, holds an Endocrine Certification in Neck Ultrasound (ECNU) and is a Certified Clinical Densitometrist (CCD). He has extensive experience performing ultrasound guided fine needle aspiration biopsies. His practice includes a range of specializations including prescribing and fitting patients with insulin pumps. Dr. Mathews' practice has drawn patients from out of state to benefit from his expertise in thyroid disorders, diabetes, cortisol problems and their Endocrine disorders.

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