Keeping Your Biological Clock Running on Time

By Mo McNulty, PhD Student

In our upcoming NPHR journal issue, PhD/MPH student Nelly Papalambros discusses how sleep is tied to many health issues, such as metabolic dysregulation and obesity, mental health issues, and even cancer. Make sure to check out her article about the public health ramifications of circadian rhythms when the journal is released in June (we’ll post links to it here!), but in the meantime, learn more about how you can avoid disrupting your circadian clock:


Various biological processes tend to occur at certain times of day. These patterns are circadian rhythms. (Source: Wikimedia Commons)

Have you ever flown across several time zones and had your sleep schedule get off track? If so, you’ve had experience with having your normal circadian rhythms disturbed. Your body has a natural biological clock that uses environmental signals like light/dark and fasting/feeding cycles to regulate processes in your body such as sleep and metabolism. Light signals are picked up by the eyes and transmitted to the suprachiasmatic nuclei (SCN) – groups of cells in the brain that send out hormone signals such as melatonin to the rest of the body in order to regulate the internal clocks of different organs.

Jet lag is just one way that disruption of our biological clocks can occur – working the third shift, or irregular shifts, and using electronics during nighttime hours can also cause disruption of circadian rhythms. However, more tools and strategies are being discovered that can help keep your natural body clock running on time.

Jet Lag

People often suffer from jet lag after crossing at least three time zones. Travelers may experience fatigue, difficulty sleeping, and problems with physical and mental tasks as a result of the internal clock being out of sync with external signals [1]. If you want to avoid these symptoms, it is helpful to think about sending the correct signals to your body clock. If you are traveling across multiple time zones but are only staying a couple days, it is a good idea to try to stay on the same sleep schedule that you were using at home. However, you may want to adjust your clock to the new time zone if you are staying more than three days [1]. This can be done by regulating your exposure to light. The table below gives recommended times for dark and light exposure on the first day after travel based on how many time zones you’ve gone through. On subsequent days, you can gradually shift your exposure to light to match the light/dark cycles of your new time zone. Additionally, a meta-analysis of randomized trials that looked at melatonin use during travel found that taking this hormone close to the desired bedtime decreased jet lag, especially among people traveling across more than five time zones [2].


Times of day to avoid light and to expose yourself to light when traveling across multiple time zones. (Source: Waterhouse, Jim, et al. [1])

Shift Work

Many epidemiological studies have indicated that there are health issues for people who do shift work. As mentioned in Nelly’s article, shift workers often have issues with fatigue and job performance [3], and women working night shifts or exposed to light at night have higher rates of breast and ovarian cancer [4] [5] [6]. A dysregulated cycle of light exposure can also lead to mood and cognitive defects [7]. Many shift workers experience constant disruption of circadian rhythms, which causes cause fatigue during the day and difficulty sleeping at night. The ideal sleep schedule is one that is consistent and at night, but many shift workers do not get to choose when they work. In this case, there are other ways that workers can try to maintain regular circadian rhythms: keeping the same sleep/wake cycles even on days off, ensuring living spaces are dark during the daytime, making sure to get ample light exposure during wake periods, and developing strategies with a doctor if difficulties maintaining a regular schedule are encountered [8].

Tips for Everyone – Protecting Your Normal Sleep and Wake Cycles

The American Medical Association now recognizes that disruption of sleep and of circadian rhythms can be caused by exposure to light at night, and they recommend new research and new technologies to combat these effects [9]. On an individual level, in order to avoid health problems linked to irregular circadian rhythms, it is useful to regulate your light exposure – light causes sleep-inducing melatonin to be suppressed. A big problem in our society is the ubiquitous presence of light-emitting screens, from televisions, computers, and other electronics. These are especially problematic because light from screens contains a high amount of blue wavelengths, which suppress melatonin more than other wavelengths of light – so avoid these before bedtime if possible [10]! Energy-efficient lighting also tends to have more blue light, but regular light bulbs generally don’t have as much, so they may be better to use during the night. Other tips to avoid disrupting your circadian cycle include making sure your sleeping area is very dark, using dim red lights if you need a night light, and wearing goggles that only block blue light if you have to be exposed to light at night [10]. Finally, make sure to get a lot of light during the daytime – it will help you be more alert, and help you get more sleep when nighttime comes around!


  1. Waterhouse, Jim, et al. “Jet lag: trends and coping strategies.” The Lancet 369.9567 (2007): 1117-1129.
  2. Herxheimer, A., and K. J. Petrie. “Melatonin for the prevention and treatment of jet lag.” Cochrane Database Syst Rev 2 (2002).
  3. National Sleep Foundation. “2012 Sleep in America Poll: Planes, Trains, Automobiles, and Sleep.” 2012.
  4. Kolstad, Henrik A. “Nightshift work and risk of breast cancer and other cancers–a critical review of the epidemiologic evidence.” Scandinavian journal of work, environment & health 34.1 (2008): 5-22.
  5. Davis, Scott, and Dana K. Mirick. “Circadian disruption, shift work and the risk of cancer: a summary of the evidence and studies in Seattle.” Cancer Causes & Control 17.4 (2006): 539-545.
  6. Stevens, Richard G., et al. “Breast cancer and circadian disruption from electric lighting in the modern world.” CA: A Cancer Journal for Clinicians (2013).
  7. LeGates, Tara A., et al. “Aberrant light directly impairs mood and learning through melanopsin-expressing neurons.” Nature 491.7425 (2012): 594-598.
  8. McMullen, Laura. “Healthy Tips for Night Shift Workers.” US News 11 Feb 2014.
  9. Weir, William. “Artificial Lighting Poses Health Risks, American Medical Association Asserts.” The Courant 20 June 2012.
  10. Harvard Health Letter. “Blue Light Has a Dark Side.” Harvard Health Letter May 2012.

Cover Photo by pixabay via pexels: creative commons

About NPHR Blog (339 Articles)
The is the blog of the Northwestern Public Health Review journal. The blog and journal are both student run and contain research articles, opinions, interviews and other content pertaining to public health.

2 Trackbacks / Pingbacks

  1. Public Health in the News – May 24, 2014 | NPHR Blog
  2. The Latest Volume of the Northwestern Public Health Review is Here! | NPHR Blog

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: