Can Working the Night Shift Cause Cancer?

Could the graveyard shift send you to an early grave? According to the World Health Organization, working overnight could raise your risk of getting cancer. Maria Cheng is a medical writer for the Associated Press. She reported on the story and explains the findings.

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FARAI CHIDEYA, host:

Could the graveyard shift send you to an early grave? According to the World Health Organization, working overnight could raise your risk of getting cancer. Maria Cheng is a medical writer for the Associated Press and she reported on the story. She's with us now.

Hi, Maria.

Ms. MARIA CHENG (Medical Writer, Associated Press): Hi, how are you doing?

CHIDEYA: I am doing great. No, the World Health Organization believes that something called a circadian rhythm has to do with the person's openness to cancer. Can you first explain what a circadian rhythm is and how it's changed if you work overnight?

Ms. CHENG: Sure. The circadian rhythm is basically your body's natural 24-hour clock. So it tells you when you should be sleeping and eating, producing certain hormones for biological functions. And it's based on the light/dark cycle. So basically you should be up when it's light and asleep when it's dark.

CHIDEYA: How much science is there out now to really look at this issue of workplace health, people working overnight? Is this the only evidence?

Ms. CHENG: Well, it was basically an analysis of all the existing evidence. So it studies that were done in the last 20 years. And what they did was they looked at studies of nurses who worked the night shifts and airline pilots. And what they found was that in those groups, they were - the women were more likely to get breast cancer and the men were more likely prostate cancer. There have also been some animal studies showing that if you switch the light/dark cycles of animals, they are more prone to get cancer.

CHIDEYA: Now, when we talk about what a night shift is, are we talking about people who literally work from, say, you know, 12 a.m. until 8 a.m. Are we also talking about people who wake up in the dark, people who might do, say, a 4 a.m. shift?

Ms. CHENG: We don't exactly have the answer to that. All the studies looked at people with varying shifts to some extent. So we can't say exactly if people who work at - start at midnight, who's finished at 6 a.m. or something like that. But the idea is basically, if you're working when you're supposed to be sleeping that interrupts your body cycle and may make you susceptible to cancer.

CHIDEYA: Melatonin, what's that? It has been mentioned in the study. What exactly is it, and how does this impact it?

Ms. CHENG: It's basically a hormone that your body produces and scientists think that it can help you fight cancer if they can help fight tumors. But the problem is, it's only produced when it's dark. So if you're working under light conditions at night, you're probably not producing as much of it as you may need to protect your body from cancer. So if you tend to work at night a lot, and your body's not producing a lot of it, your levels may be lower, which may make you more vulnerable to cancer.

CHIDEYA: Now, melatonin is something that you can pick up in some health food stores. Is anyone discussing or analyzing whether or not these available melatonin tablets have any impact on these issues?

Ms. CHENG: Well, the people have taught about whether or not you could take that as a supplement, but they don't think it's a good idea to take it in the long-term because then your body loses the ability to produce it itself, which is not a great idea.

So basically, if you're working the night shift, what you should try to do is make sure you have this light and dark balance, so that even if you're working at night, you're still getting some amount of darkness when you're sleeping.

CHIDEYA: Tell me more about what you mean by that? How do you - how much darkness do you need? Are you saying that people should have curtains up and, you know, sort of black-out curtains in they work the night shift?

Ms. CHENG: Well, that's what some of the scientist suggested that it's really important to maintain this balance between light and darkness for your body.

So the problem is that a lot of people who work night shifts aren't entirely to switch their systems. You know, when they're days off, they still want to go and see their friends and have a normal life. So they're basically overextending themselves so they don't get enough darkness.

If you were able to completely switch yourself so that you were up during the night when you had to be, and then sleeping in darkness during the daytime, that might be okay, but it's this constant switch that they think is dangerous.

CHIDEYA: Some people who work the night shift probably could do their work at other times. Other people, you always need nurses, you always need people in emergency rooms. You need a lot of people who work at night in a mandatory way. Is there any sense of how this could impact the business world or do you think people will largely ignore a study like this?

Ms. CHENG: I think obviously it's going to have an impact on the business community. It is, right now, just probable tag. So they haven't determined conclusively that it causes of cancer. There could be some other things that people are doing, which increases their cancer risk, but the advice from the scientists seem to be that, if you can avoid working on a night shift for a long period of time, or at least avoid this conflict, which is that screw up your body's biological clock, that would probably help.

CHIDEYA: Now, the World Health Organization has been careful to say this research is not conclusive. When it comes to being better safe than sorry, what's the bottom line here?

Ms. CHENG: Again, it's just really important to maintain that balance between light and dark, so that if you are working at night, it's very important to get some sleep in a dark area, to make sure that your body has that time to produce melatonin to ensure that your levels aren't low enough that you might be susceptible to cancer.

CHIDEYA: Very briefly, what's the next step for someone like you, who's covering the story?

Ms. CHENG: Well, obviously, it's something that we'll continue to follow. More studies need to be done to see if they will get the same results in different populations and people who aren't nurses and not airline pilots to see if it applies to other populations. And basically, just watch as to see what things that's can be done to prevent this. If there are certain kinds of light that could be used that wouldn't inhibit melatonin production and other measures that people can do to protect themselves.

CHIDEYA: Maria Cheng, thanks so much.

Ms. CHENG: My pleasure.

CHIDEYA: Maria Cheng is a medical writer for the Associated Press, based in London. She talked with us about the possible link and cancer and people who work the night shift.

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