While many kids (and adults, too) might prefer to sleep with a light on, research shows that exposure to artificial light after the sun goes down can disrupt healthy body function and is associated with an increased risk for cancer. So turn off your computers, TVs, and nightlights for kids, and learn to embrace the nighttime darkness.
Light, Circadian Rhythms and Melatonin
Our bodies are governed by a 24-hour biological clock, the circadian rhythm. The circadian rhythm regulates when we sleep and wake, and governs many other important biological processes. Melatonin, one of the main hormones responsible for maintaining this cycle, is normally produced in the dark. Light at night suppresses the pineal gland’s secretion of melatonin and disrupts the circadian rhythm. Low melatonin can contribute to a wide variety of health conditions, from sleeplessness to migraines.
Increased Cancer Risk
The circadian rhythm also regulates important processes that modulate tumor activity. Several studies have found evidence that melatonin directly inhibits tumor growth and development.[1,2] Even short-term exposure to bright, white light at night can interfere with this effect.
Women working the night shift show increased risk for breast cancer, and this effect is attributed to their exposure to light at night. These observations and a multitude of laboratory studies have led researchers to conclude that “shift-work that involves circadian disruption is probably carcinogenic to humans.” Interestingly, blind women show a lower risk for breast cancer as well, strengthening the link between light exposure and cancer risk.
Importance for Children
Children may be especially sensitive to artificial light at night. One study found that in children, melatonin activity was suppressed by light at night almost twice as much as it was in adults. Childhood experiences, and even in utero conditions, can influence the risk of cancer later in life. Adolescence and other developmental periods are particularly important and circadian disruptions during these periods can be very detrimental.
Researchers note that “ill-timed electric light exposure to a child may disrupt circadian rhythmicity and contribute to increased risk of cancer later in life.” They suggest that parents avoid night-lights for children from birth onward, and that parents should also use dim red light sources when feeding or caring for a child during the night.
Simple Steps for Reducing Exposure to Nighttime Light
1. Teach your child to sleep without a nightlight. While it can sometimes be a difficult transition to remove nightlights for kids, most children will eventually get comfortable sleeping in the dark. Make the transition slowly. For the first few nights, keep a dim nightlight on in the room. Them, remove that light, and keep the hallway light on with the door cracked. Slowly, work up to closing the door and having your child sleep in complete darkness.
2. Keep a dim, red nightlight in the hallway and bathroom. Red light is better than blue light for nighttime exposure, as blue light is especially disruptive to melatonin. Also keep a red light in your room that you can turn on if you need to get up in the night.
3. Remove alarm clocks, nightlights, and bright electronics from bedrooms. Your room should be as dark as possible at night, and even the lights on an alarm clock can produce unnecessary and harmful light.
4. Use blackout curtains. For those living in the city with bright streetlights outside, blackout curtains can help keep your home free of artificial light.
5. Avoid watching TV or using your computer or phone before bed. Avoiding these artificial lights at bedtime will likely help you to fall asleep easier and get a healthier night’s rest.
 PLoS One. 2014 Aug 6;9(8):e102776.
 Cancer Res. 2005 Dec 1;65(23):11174-84.
 Lancet Oncol. 2007 Dec;8(12):1065-6.
 Epidemiology. 2005 Mar;16(2):254-8.
 J Clin Endocrinol Metab. 2014 Sep;99(9):3298-303.
 Cancer Epidemiol Biomarkers Prev. 2012 May;21(5):701-4.
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