How bad is it for you to sleep with the light on ?

April 20, 2012 3:46 AM

How bad is sleeping with the light on? I have checked google! - more inside.

I quite often wake up in the middle of the night to read and switch the light on,or if on my own, often fall asleep with the light on. I recently saw a study, Israeli,I think, suggesting that this is terribly dangerous and that even switching on the light if you are going to the bathroom in the middle of the night could be dangerous and increase your likelihood of getting cancer(?!) I can sleep quite happily with the light on and find it comforting and wake up rested -is there really a problem?

posted by hitchcockblonde to health & fitness (11 answers total)

....based on everything I know about electricity, light patterns, and such, I can't think how sleeping with the light on even would lead to cancer in the first place. I actually feel somewhat like channeling Morbo and saying "Cancer does not work that way."

Think about how many kids ask to have a light on at night while they're asleep; and now consider the rate of childhood cancers. If leaving the light on while you're asleep, the rate of childhood cancers would be a lot higher, wouldn't it?

The only danger you face by leaving a light on while asleep is an elevated electricity bill, I think.
posted by EmpressCallipygos at 3:55 AM on April 20, 2012

I guess this may be the study you're remembering.

IANAD. I generally agree with EmpressCallipygos that it's very unlikely that there's a direct relationship between sleeping with the light on and increased rates of cancer.

However, some studies suggest that poor sleeping habits may be a risk factor in developing cancer.

Taking into account the generally accepted idea that sleeping in a brightly-lit environment can contribute to poor sleep, it's not out of the question to imagine an indirect connection between sleeping with the light on and increased rates of cancer.
posted by syzygy at 4:06 AM on April 20, 2012 [1 favorite]

Something normally doesn't cause cancer or not. You need to look at how likely it is: sleeping with the light on is almost certainly amazingly low on the "causes cancer" scale. Whereas smoking 200 cigarettes a day is probably amazingly high on the scale. You likely have bigger risks to bad health or death from many other things you do. Don't worry about it.
posted by devnull at 4:09 AM on April 20, 2012

In the second study abstract I linked to above (from the journal Cancer), the conclusion is:

Shorter duration of sleep significantly increases risk of colorectal adenomas. The authors' results suggest sleep duration as a novel risk factor for colorectal neoplasia.

This article from the University of Maryland Medical Center talks about links between low melatonin levels and breast and prostate cancers (with links to supporting materials at the end of the article).

As I understand it, exposure to light is one of the main things that affects your body's production of melatonin - whether you're sleeping or not. I believe I've even read that short exposure to bright light in the night (say, turning on the light to go to the bathroom) can interrupt melatonin production.

It's important to remember that science trumps common sense. Had you asked 5 years ago whether sitting down at work increases your risk of heart disease, most common sense answerers would have scoffed at the idea. In the meantime, studies have shown a clear link between sitting down all day at work and an elevated risk of heart disease.

I suggest you ignore common sense answers and look for scientific studies on the matter.
posted by syzygy at 4:31 AM on April 20, 2012 [3 favorites]

I meant to include the following two quotes from the previously-mentioned UMMC article on melatonin:

Breast Cancer:

Several studies suggest that low melatonin levels may be associated with breast cancer risk. For example, women with breast cancer tend to have lower levels of melatonin than those without the disease.

Prostate Cancer:

Studies show that men with prostate cancer have lower melatonin levels than men without the disease. In test tube studies, melatonin blocks the growth of prostate cancer cells.

Abstract from a study on the link between melatonin and breast cancer published in the Endocrinology Journal.

Antiproliferative action of melatonin on human prostate cancer LNCaP cells.

Recent experimental evidence suggests that melatonin, the major pineal hormone, might possess oncostatic* properties.

*oncostatic is a synonym for anticarcinogenic

Oncostatic action of melatonin: facts and question marks.

a hypothesis of the oncostatic action of melatonin was put forward. The mechanism of the postulated action is complex and probably includes: 1) modulation of the endocrine system; 2) modulation of the immune system; 3) the direct oncostatic action of melatonin on tumor cells. The latter includes the recently discovered anti-oxidative action which probably plays an important role in the countering the DNA damage during the radiation challenge or the exposure to chemical carcinogens. It also includes the antiproliferative and pro-apoptotic effects exerted via melatonin receptors expressed by tumor cells.

posted by syzygy at 4:42 AM on April 20, 2012 [2 favorites]

IIRC, the "even turning the light on when you go to the bathroom" part came from a Daily Mail article, and was a journalistic gloss on one of these studies. But there is definitely evidence (as syzygy cites) that screwing with your sleep cycle can increase cancer risk (shift workers are well known to be at higher risk for many cancers, for example).

I've glanced over some of the "light at night" studies from the Israeli group in the news article above, and it's not clear to me how well they account for confounding factors; they seem to rely on satellite light information (night brightness surely must correlate with lots of other factors like urbanization, income level, noise level, population density, and it's not clear to me how well these factors are controlled for) and self-report of bedroom brightness level (which seems like it could be subject to bias). I'm not saying they're bad studies, just they're not the be-all and end-all.

I don't know you or your lifestyle or your other cancer risk factors, but I would guess if you're like most people you're doing other things that increase your cancer risk more than sleeping with the lights on.
posted by mskyle at 6:59 AM on April 20, 2012

I think a good general life policy is not to change your behaviour based on studies that appear in medical journals. At the point in which they are appearing in journals, they have not yet been reproduced or the results substantially investigated. And the bar for statistical relevance is really quite low (something increasing your risk factor by one tenth of one percent is easily journal worthy).

If something(especially something as ubiquitous as household lights) is actually discovered to be harmful, you will be warned about it in more direct ways, and legislation will follow. Think cigarettes, mercury, and lead.
posted by 256 at 9:02 AM on April 20, 2012

256 something increasing your risk factor by one tenth of one percent is easily journal worthy

I find it very hard to believe that a significance of 0.1% would be journal worthy, unless the article's conclusion was that the study determined there was no significant link between the cause and effect.

Feel free to correct me if I'm wrong, but I'm 99.9% certain that no respectable medical journal will publicize an article whose conclusion is that X leads to an increased risk for Y when the underlying study shows no more than a 0.1% increase in risk of Y when X is a factor.
posted by syzygy at 9:29 AM on April 20, 2012

I suggest you ignore common sense answers and look for scientific studies on the matter

I really wouldn't put it that far. Scientific studies are great but as 256 mentioned, the moment they appear in journals they have not yet been reproduced or substantially investigated.

Case in point: saturated fat. There once was a study linking saturated fat and increased level of cholesterol. People took it at face value and started to jump on the trans fat bandwagon. Turned out trans fat is even worse. As for saturated fat and cholesterol? Yes - the link holds but turns out there are different kinds of cholesterol involved.

As for common sense before this hoolabaloo? Eat saturated fat sources (tallow, lard, fish) normally. Don't over do it but no need to shy away from it either.

And that is my philosophy in general. Science is great and it helps us understand our world better. But science of these disciplines as opposed to the 'hard' sciences is incredibly complex with results that can be interpreted every which ways. Take the results with a grain of salt and go with common sense in the meantime.
Common sense and moderation.
Lights in your bedroom? Probably won't do you harm if you do it once in a while. To have 100W lightbulb near your face for every single night the rest of your life? Better not.

OP - if you're really concerned, connect your reading light to a timer. You can fall asleep as normal but the light will turn off after some time.
posted by 7life at 11:42 AM on April 20, 2012 [1 favorite]

syzygy, I think that really all depends on what your baseline risk was - imagine if your baseline risk of getting X disease is .1% (i.e. one in 1000, so much lower than your chance of getting breast cancer), and exposure to Y environmental contaminant (or whatever) increased your risk by .1% to .2%. That's a 100% increase in the number of cases you would expect to see in a population, and very important from a public health perspective (and therefore worthy of being published) but of limited importance to any given individual.

Communicating risk is really hard.
posted by mskyle at 11:44 AM on April 20, 2012

There are so many cancer risks in modern life. Sleeping with the light on should, I think, fall pretty far down the line.

If you sleep well and wake up rested, that's the main concern here. (Personally, I sleep very poorly with the lights on.)

If this is a concern for you, try stepping down over the course of 3-6 months. Spend a month gradually adjusting to sleeping with a lamp on instead of the overhead light. Then another few months gradually reducing the wattage. 2 weeks with a 150-watt bulb, 2 weeks with a 100-watt bulb, and so forth.

Eventually you'll be down to sleeping with just a 10-15 watt night light on, and at that point, you're effectively sleeping in darkness. Presto!
posted by ErikaB at 10:44 PM on April 20, 2012