Light Can Interrupt Your Circadian Rhythm

A light bulb company from Florida has decided to put warning labels on the light bulbs they manufacture to tell you that artificial light can have health consequences: light can interrupt your circadian rhythms.We do not easily see that it should matter whether you use artificial light at night or not.


What we do know is that in the evening when we close our eyes and shut out the light the melatonin production gets elevated, we get sleepy, and we fall asleep. During our sleep the immune system receives a boost from the higher melatonin blood concentration, while cortisol takes a rest and levels are lower overnight. Melatonin is also a powerful anti-cancer agent and this would fit in with the study that found that a loss of the clock gene in shift workers was correlating to a worse prognosis regarding their breast cancer.

There are other diseases that can develop when the circadian rhythm is not maintained. Here are a few examples: neurodegenerative disease, cancer, depression, and sleep disorders.

This link shows how the internal central clock in the suprachiasmatic nucleus of the hypothalamus is responsible for keeping time inside of us. The suprachiasmatic nucleus is situated just above the optic chiasm, hence the name.

The clock gene influences the peripheral clock via the clock genes in each organ to be synchronized. If you disregard your internal clock, expose yourself to prolonged artificial lighting and delay going to sleep in time you will create a disorganized central/peripheral rhythm, which weakens the immune system, disrupts your normal hormone rhythms, and ultimately this can lead to disease.

Breast cancer from interrupted circadian rhythm

Women in California were followed with regard to developing breast cancer and nightly exposure to artificial light.

In this study the authors found a 1.34-fold higher breast cancer risk in premenstrual women exposed to high levels of ambient light at night compared to women who were not.

Similarly, a 2014 study showed a difference with regard to breast cancer rates in women who were working night shifts and women who worked normal hours.

The study showed a loss of clock genes in shift workers with breast cancer that was associated with a worse prognosis of their breast cancer compared to those who were not shift workers and had normal clock genes.

Is it a good idea to tell people that light bulbs can be harmful?

Fred Maxik, the Florida based Lighting Science Group chief officer thinks it is a good idea. Dr. Paolo Sassone-Corsi, the director of the Center of Epigenetics and Metabolism at the school of medicine at University of California Irvine who has authored many studies on the negative effect of artificial lighting on the circadian rhythm also thinks that labeling light bulbs is a good idea. He cautions that there are even more powerful light sources like TV’s and computers that can disrupt the circadian rhythm the later it gets in the evening. “And think about how many people look at Facebook at 2 a.m. That is way more disruptive, but this is certainly a good start; we need to keep increasing awareness in a larger population that light at the wrong time of day can harm you” Dr. Sassone-Corsi added.

It is somewhat nebulous what effects a disruption of the circadian rhythm has in our system. But we do know that sleep deprivation can cause overeating and obesity, memory loss, short attention span, diabetes, depression, car accidents, sudden cardiac arrest and sudden cardiac death due to deadly electrical heart rhythms (ventricular fibrillation).

This 2015 study suggests that melatonin should be used to treat people who are involved in shift work. This will help to reset the circadian rhythm to normal.

Origin of circadian rhythm disorders

Sleep disorders can start in childhood, usually when school starts with structured days and normal bedtime hours, followed by school holidays and weekends where late bedtime hours or irregular sleep habits are the rule. Circadian rhythm disorders are not disorders of sleep quality, but rather disorders in timing of sleep (Ref.1). Circadian rhythm disorders start usually when the child enters school, but can develop as late as in adolescence. 10 to 18% of children and adolescents have circadian rhythm disorders. It is not known why some children find it easy to switch between the irregular sleeping habits of summer to the regular sleeping habits during school days. But others are not able to switch and have problems in school with inattention, daytime sleepiness, irritability, hyperactivity and combativeness. Circadian rhythm disorder tends to persist and can turn into adult circadian rhythm disorder. There are also morning types and evening types (in medical lingo morning chronotypes and evening chronotypes).

Delayed sleep phase disorder

One of the most frequent subtypes of circadian rhythm disorder is the delayed sleep phase disorder. This is what is often found in adolescents who push for a later and later bedtime. The fact that they sleep in until 11 AM or 1 PM reinforces it. They like to shut their windows with a black curtain to keep the sunlight out. At night they like to spend time in front of a computer or the TV. They like to go to sleep only at 1, 2 or 3 AM. They may not be aware what is happening to them: the lack of morning sunlight exposure in the early morning hours of the day leads to a delayed setting of the dim light melatonin onset (DLMO) at the end of the day, which is regulated through the suprachiasmatic nucleus (a part of the hypothalamus). By taking frequent blood or saliva melatonin levels researchers have been able to measure corresponding melatonin levels at the time of the DLMO.

We know from research with astronauts in space travel that melanopsin is produced in the blue-light-sensitive photopigment in the ganglion cell layer of the eye. Melanopsin travels from there along the optic nerve into the suprachiasmatic nucleus, where it helps to set the circadian rhythm for the day.

The day is defined by first opening our eyes when we wake up, getting the first melanopsin dose in the circadian rhythm headquarters of the hypothalamus; two yours before we fall asleep we have the dim light melatonin onset where melatonin is just starting to rise, which makes us gradually tired. Maybe the cave men and women sat around the fireplace and told each other stories. We could listen to soft music in a less brightly lit area.

Treatment of delayed sleep phase disorder

It is important to note that people with a delayed sleep phase disorder (DSPD) do not have a sleep disorder: they have normal sleep at an abnormal time (Ref.1)

Here is how the sleep specialist treats delayed sleep phase disorder.

  1. Exposure to sunlight or to blue LED light at the time of awakening for 20 minutes to 1 hour is key to resetting the circadian rhythm to an earlier point than has been the case. This involves that the child, adolescent or adult has to get used to setting an alarm clock to a desired time in the morning. In order the preserve the resetting of the circadian rhythm towards the evening it is important that from 5 to 6 PM in the evening exposure to the bright lights is avoided. This includes light emission from TV’s, i-phones or computers. The eye would otherwise reset the circadian rhythm via the melanopsin mechanism to a later time.
  2. Melatonin treatment is used to advance or delay circadian rhythms. Melatonin also has a sedating effect, but only about 20% respond to that within 30 minutes by falling asleep. The doses in commercial products override the circadian rhythm effect. Sleep experts use much smaller doses of melatonin to reset the internal clock. Thinking of an adolescent who goes to sleep at 2 AM, the DLMO would be at midnight. To phase advance an individual like that a small amount of melatonin (0.5 to 1.0 mg) would be given at 6 to 8 PM (that is 4 to 6 hours before the DMLO point or 6 to 8 hours before the previous bedtime). The morning exposure to bright light works together with the early evening dose of a tiny dose of melatonin, which by itself is not enough to put the person to sleep at that time.
  3. Supportive sleep hygiene methods: It is important that the parents understand the underlying problem. If necessary, they may have to seek the advice of a sleep expert and discuss the details with him/her. 2 hours prior to bedtime the child needs to be exposed to dim light, which is light that does not have blue light in it. The level of dimness is such that reading is difficult. No TV, no cell phone or I pad is allowed. In this dim light atmosphere melatonin is expressed normally and will be produced and released by the pineal gland in higher amounts. Establish a regular bedtime with which all family members can agree. This is best kept on school days, holidays and weekends. If you would sleep in, you would switch your time machine in your head to another time zone further west and it would be an effort to switch it back! There are many children and adolescents who can switch back and forth easily, but the person with DSPD cannot switch easily and would get stuck again in the familiar late sleeping pattern.

Avoid cola and other caffeinated beverages, including green tea, as they stimulate. The bedroom should be dark, quiet and comfortable. Sound machines have not been shown to enhance sleep (Ref.1).

Light Can Interrupt Your Circadian Rhythm

Light Can Interrupt Your Circadian Rhythm


Circadian rhythm disturbances are more common than previously thought of. There is a certain percentage of children who enter the school system that develop delayed sleep phase disorder. This often stays with them into adolescence and can even carry on into adulthood. Two simple tools have been shown to treat this: early morning light exposure for 20 minutes to 1 hour and a small dose of evening melatonin to reset the circadian rhythm. There likely are thousands of untreated people with circadian rhythm disorders. As not all circadian rhythm disorders are the same it is advisable to seek the advice of sleep disorder expert, if sleep patterns are problematic.



1. John H. Herman, Chapter 5, 35-43. “Circadian Rhythm Disorders”

Principles and Practice of Pediatric Sleep Medicine

Second Edition. Stephen H. Sheldon et al., 2014, Elsevier Inc.

About Ray Schilling

Dr. Ray Schilling born in Tübingen, Germany and Graduated from Eberhard-Karls-University Medical School, Tuebingen in 1971. Once Post-doctoral cancer research position holder at the Ontario Cancer Institute in Toronto, is now a member of the American Academy of Anti-Aging Medicine (A4M).