The Melatonin Effect: Could Nighttime Light Cause Female Cancers?

The Melatonin Effect: Could Nighttime Light Cause Female Cancers? |Women's Health | Sara Gottfried, M.D.Are you routinely awake at night with the lights on? Your health might be more at risk. For one, studies on almost two hundred thousand [1] night-shift workers showed increased risk of coronary heart disease among women. Other studies show correlations between night-shift work and higher rates of metabolic syndrome,[2] inflammation,[3] obesity,[4] and depression/anxiety.[5] Beyond these worrisome health risks, two diseases particular to women are associated with working at night: breast cancer[6] and ovarian cancer.[7]

 If there’s one disease that women worry about, it’s breast cancer. The awareness is largely due to research fundraising organization Race for the Cure, which branded breast cancer awareness with the now-renowned pink ribbon logo. Other women’s reproductive-organ cancers are becoming better known, such as ovarian cancer. Despite the awareness, do women know about the relationship between nighttime lighting and higher rates of these cancers? Popular medical advice sites such as the Mayo Clinic, the NIH, the American Cancer Society, and Web MD do not mention nighttime darkness as a natural preventative measure. Rather, they focus on physical activity and nutrition; the darkness effect remains in the dark.

The Melatonin Connection

The research on a night-shift worker’s elevated risk of breast cancer and ovarian cancer implicates low levels of the hormone melatonin; peak levels are released during darkness. If you are awake between 9:00 p.m. and 9:00 a.m., especially under bright lighting, your body suppresses melatonin release. As a result, melatonin’s normal influences on the body are diminished.

A study on Danish military women explains it this way:

Night work can disrupt circadian rhythms, suppress production of the pineal hormone melatonin and result in sleep deprivation, all of which affect hundreds of metabolic and physiological processes, including hormone production, cell cycling and apoptosis, which in turn may increase the initiation, progression and growth of human tumors, including breast cancer.[8]

Who Is at Risk?         

Many professions require nighttime shifts. Whether you’re working in a hospital, on a red-eye flight, policing the streets, or working online from home, your job necessitates you being awake during darkness. The studies equated higher rates of breast and ovarian cancers with at least three night shifts per week. However, we are unsure about how far-reaching this issue might be, especially since more people stay up late these days, “hanging out” in the Internet. The jury is still out on whether a regular night owl is as affected by low melatonin as much as the night-shift nurse. Therefore, to be better safe than sorry, it behooves any woman who’s awake at night with the lights on to try to combat decreased melatonin by raising its levels alternatively.

How to Raise Melatonin Levels

Here are three ways to elevate melatonin levels for women with overexposure to nighttime lighting.

  1. Replace some daylight hours with darkness. Create a darkened atmosphere to counterbalance the hours of light in order to provide “night time” for your body. For example, draw heavy black curtains in your bedroom during sleep hours. This allows night-shift workers to move their personal darkness hours to a different time of day, releasing peak melatonin levels in kind.
  2. Take melatonin supplements. I recommend 0.3-5mg of melatonin four hours before going to bed. This tiny dose of melatonin will cause levels to spike in your body and then decline. Your body will recognize the decline so your pineal gland will start to make more melatonin, which will allow you to sleep more soundly when you go to bed several hours later.
  3. Practice daytime mini-savasana. Savasana (pronounced ShavAH-suhna) is the last pose of a yoga session. It is dubbed the “corpse” pose because you lie still and flat on your back, focusing only on your breath. As a result, savasana allows for restoration and rejuvenation after a yoga workout. Savasana is also correlated with (you guessed it) higher melatonin levels and, therefore, helps you sleep. But you don’t have to wait for yoga class or bedtime to do savasana, rather, you can integrate it into your day to increase overall melatonin levels. Check out this video of a mini-savasana.

While it’s still unclear whether any woman who routinely lacks nighttime darkness is at higher risk of breast or ovarian cancer, by following the above tips, you’ll be able to counterbalance nighttime lighting’s effect on the hormone melatonin, enabling you to reduce your risk for cancers and other health issues. It may all come down to having a good night’s sleep.

Interested in more information on female hormone balance? Check out my book The Hormone Cure.


[1] Kawachi, I., et al. “Prospective study of shift work and risk of coronary heart disease in women.” Circulation 92, no. 11 (1995): 3178-3182; Vetter, C., et al. “Association between rotating night shift work and risk of coronary heart disease among women.” Journal of the American Medical Association 315, no. 16 (2016):1726-1734.

[2] Szosland, D. “Shift work and metabolic syndrome, diabetes mellitus and ischaemic heart disease.” International Journal of Occupational Medicine and Environmental Health 23, no. 3 (2010):287-291.

[3] Sookoian, S., et al. “Effects of rotating shift work on biomarkers of metabolic syndrome and inflammation.” Journal of Internal Medicine 261, no. 3 (2007):285-292.

[4] Peplonska, B., et al. “Association of rotating night shift work with BMI and abdominal obesity among nurses and midwives.” PloS One 10, no. 7 (2015):e0133761.

[5] Scott, A. J., et al. “Shiftwork as a risk factor for depression: a pilot study.” International Journal of Occupational and Environmental Health 3, no. 2 (1997):S2-S9; Kalmbach, D. A., et al. “Shift work disorder, depression, and anxiety in the transition to rotating shifts: the role of sleep reactivity.” Sleep Medicine 16, no. 12 (2015):1532-1538.

[6] Hansen, J., et al. “Nested case–control study of night shift work and breast cancer risk among women in the Danish military.” Occupational and Environmental Medicine 69, no. 8 (2012):551-556; Grant, S. G., et al. “Melatonin and breast cancer: cellular mechanisms, clinical studies and future perspectives.” Expert Reviews in Molecular Medicine 11 (2009):e5.

[7] Bhatti, P., et al. “Nightshift work and risk of ovarian cancer.” Occupational and Environmental Medicine 70, no. 4 (2013):231-237.

[8] Hansen, J. “Nested case-control study…” Occupational and Environmental Medicine 69, no. 8 (2012):551-6.