Shift Work Is Bad for Health

Shift work is the working of any hours outside of normal daytime hours. Unfortunately, since many people do it, shift work is bad for health.

The most common variations in shift work are the “swing shift”, work starting in mid-afternoon and ending late at night, and the night or “graveyard” shift, starting late at night and ending early in the morning.

I’ve worked plenty of both of these shifts in my life, and may have spent more hours working swing shifts than on the day shift. These hours may have contributed to my former ill health — in fact I think it likely.

A great deal of research has found associations between shift work and a number of diseases, notably heart disease and cancer.

A study that looked at workers in a paper mill found that increasing exposure to shift work strongly increased the risk of heart disease.1

Those who had worked more than 11 years on shifts other than days had more than twice the risk of heart disease, and those who worked more than 16 years had almost triple the risk.

So you can see that the risk isn’t small.

Shift work is associated with cancer too. For instance, women who worked the night shift had a 60% increased risk of breast cancer.2

Shift work has been extensively studied, and all of the studies haven’t found such a huge increase in risk as those cited here. Others have found differences in smoking rates and dietary habits that could account for much of the difference. For example, it seems likely that shift workers eat more junk food than those on the day shift. Often, the only food to be found on a night shift comes from a vending machine.

But there are good reasons to think that shift work in itself is harmful.

A recent study written up in Scientific American found that bright light speeds up aging in mice.3 The mice experienced a decrease in bone density, more inflammation,  and muscle weakness. Restoring the mice to health was a simple matter of turning off the bright lights at night.

Exposure to light at night disrupts circadian rhythms, which are so important for health. One of the main consequences of light exposure at night is that it greatly disrupts the production of melatonin, a hormone that promotes sleep and good immune function.4

The disruption of melatonin is particularly sensitive to blue light, i.e. the kind that comes from artificial lighting and from computer screens and phones.

What you can do

  1. If you work a non-day shift, you can either get a day shift or find another job. While this is easier said than done for many people, if I had a serious health problem I would strongly consider it.
  2. If you must work a non-day shift, use blue-blocking glasses. You might get looked at funny, but your health is more important.
  3. Be cognizant of light at night when at home too. My sleep significantly improved when I installed blue-light-blocking programs on my computer and my tablet. Get f.lux for computer, and Twilight for Android phone or tablet. Both are free and effective. They can be set to dim at sunset automatically, so you just set and forget.
  4. Melatonin supplementation. Personally, I’ve had bad experiences with this. Taking melatonin at night before bed has left me so groggy in the morning that I swore off it. But low doses may work for others.

Shift work and exposure to light at night are associated with cancer and heart disease.

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  1.  Knutsson, Anders, et al. “Increased risk of ischaemic heart disease in shift workers.” The Lancet 328.8498 (1986): 89-92.
  2. Davis, Scott, Dana K. Mirick, and Richard G. Stevens. “Night shift work, light at night, and risk of breast cancer.” Journal of the national cancer institute 93.20 (2001): 1557-1562.
  4.  Cajochen, Christian, et al. “High sensitivity of human melatonin, alertness, thermoregulation, and heart rate to short wavelength light.” The journal of clinical endocrinology & metabolism 90.3 (2005): 1311-1316.

Leave a Comment:

Chris Nahr says July 26, 2016

Regarding your suggestion #3, current iOS versions have a built-in display setting called Night Shift that will shift display colors towards a warmer, more yellow and less blue tone during adjustable night hours (eg 8 pm to 6 am). iOS users should certainly enable that feature.

Steve Parker, M.D. says July 26, 2016

Night shift work is also linked to higher risk of type 2 diabetes, at least in women.

Matt.E says September 16, 2016

I don’t do shift work, but I work a part-time morning job in a basement entirely lit up by intense led lights.

I always feel so fatigued after, even though the shifts are only 5 hours and the workload quite easy.

Do you think I’m running the same risks as shift workers?

    P. D. Mangan says September 16, 2016

    Matt, the only thing that occurs to me is that your morning light is not natural and that that is doing something to make you fatigued. You should get exposure to bright sunlight in the morning if possible. The shift workers’ health seems to be more affected by circadian rhythms and sleep disruption, not, so far as I know, from lighting itself.

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