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Melatonin & Breast Cancer

There are components of our diet that may increase cancer risk by mimicking the role of light pollution in melatonin suppression.

December 30, 2010 |
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For billions of years, life on the planet Earth has evolved with about 12 hours of light and 12 hours of dark. We discovered fire awhile ago, but have only been using candles about 5,000 years and electric lighting for only about a century. This is what the country used to look like. Then 20 years later. 20 years more years. And then estimated about 20 years in the future.
Our skies used to look like this. Now they look like this. The photo on the left was taken during a blackout. These days, this is the only milky way our children will likely ever see.
But so what? Does it have an effect on our health?—the light, not the candy bar. Let’s find out. You may have heard that light at night increases breast cancer risk. Is this fact or fiction? Well, two reviews were published last year assessing the existing evidence. Electric light causes cancer? Surely you’re joking.
Well, let’s look at the evidence. Smack dab in the middle of our brain is the pineal gland, the so-called “third eye.” And it’s got only one function: produce melatonin in the dark. It’s hooked up to our eyes and at dawn, the gland shuts down. Then at night it turns back on. That’s how our internal organs know what time of day it is: they sense the level of melatonin in our blood stream.
And melatonin is thought to suppress cancer growth, kinda like putting cancer to sleep at night. Let’s test the theory: If that’s true, should blind women have more breast cancer or less breast cancer? Less, right? Because their pineal gland never gets turned off by the sun. And guess what? Blindness is indeed protective against breast cancer. Cuts your risk in half.
What about shift workers who work in the middle of the night? Increased risk, right? Melatonin production is interrupted. What if you live in neighborhood with really bright street lights. Increased risk—they took satellite photos and the brighter neighborhoods seemed to correlate with greater breast cancer risk.
Anyways, fact, but what does this have to do with nutrition? Last year, for the first time ever, melatonin levels and food choices were studied. The Harvard Nurse’s Study, found two foods significantly associated with melatonin suppression—like a bright light at night, which is bad.
They looked at fruits, vegetables, nuts, bread, meat, and dairy. In which group were the offenders found? Both meat and dairy intake were associated with lower melatonin levels, which may help explain why they found that meat and dairy intake in adolescence was associated with breast cancer risk later in life.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring watch the above video. This is just an approximation of the audio contributed by veganmontreal.

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Dr. Michael Greger

Doctor's Note

Please feel free to post any ask-the-doctor type questions here in the comments section and I’d be happy to try to answer them. And check out the other videos on melatonin. Also, there are 1,686 other subjects covered in the rest of my videos--please feel free to explore them as well!

For some context, please check out my associated blog posts: Breast Cancer and DietMushrooms for Breast Cancer Prevention, and Breast Cancer & Alcohol: How Much Is Safe?

If you haven't yet, you can subscribe to my videos for free by clicking here.

  • VegeMarian

    I wonder whether the data show any correlation between meat and dairy intake at other times of life (not just adolescence) and breast cancer risk.

    • Michael Greger M.D.

      We know, based on studies of breast cancer risk due to exposure to ionizing radiation, for example, that since invasive breast tumors may take decades to manifest, dietary exposures during adolescence may be particularly important.

  • AllVegan

    There are many links between meat and dairy consumption and breast cancer. However I think the most compelling is the link between dairy and breast cancer. In studying the geographical occurance of breast cancer, researchers have found that in places where dairy is not part of the average diet like Japan the incidence of breast cancer is very low. However they have also found that when Japanese women migrate to high dairy consumption countries like the US and adopt the countries diet their breast cancer risk becomes the same as the average population. The link can not be clearer. Do not put bovine breast milk into your body and reduce your breast cancer risk.

    • Michael Greger M.D.

      I agree that we were designed to be weaned from milk as toddlers (and stick to breasts of our own species) but the latest meta-analysis of prospective cohort studies did not find a convincing relationship between cow’s milk consumption and breast cancer:Forest plot of prospective cohort studies looking at milk consumption and breast cancer risk

  • AllVegan

    I find that interesting, do you think that study is reliable? The study differentiates between dairy products and milk suggesting that dairy products, reduce breast cancer risk but Milk does not.

    I know of several studies including the Harvard nurses study which show a link between meat and dairy consumption and breast and bowel cancers. Two areas of the body which are affected by hormones, which high fat diets seem to increase in women. As well as the hormones in cows milk itself.

    There is also the research done by Dr T. Colin Campbell. Where he could turn on and off the cancer in rats by regulating the amount of casein in their diet.

    It seems odd based on the number of studies I have seen sited that show a correlation that this study should find none.

    • Michael Greger M.D.

      It isn’t “a” study, but a meta-analysis, meaning it’s an attempt to pool the results of multiple studies together, in this case (as you can see in the above graphic) more than a dozen. After pooling the results from these studies they did not find that milk intake was significantly associated with breast cancer risk (in humans).

  • kerleyc

    Does melatonin have an important interaction with other human diseases?

  • Michael Greger M.D.

    Also be sure to check out my associated blog post Breast Cancer and Diet!

    • Jackie

       Dr. Gregor – the colon is missing in the above link, creating a broken link ;)

      • Michael Greger M.D.

        Thank you so much for pointing that out! Should be working now

  • Krystle

    Are melatonin supplements safe? I take 5mg at night to help with falling asleep. Do you know of any studies showing risk factors there?

  • Julie Arkinson

    In which plant food can we find melotanine?
    Are supplements safe?

    • Sebastian Tristan

      Raspberries. Dr. Gregger has a link for this information.

    • Joe

      Tart cherries have a high amount. But the best way to boost it is to get into a good sleep rhythm and to make sure your room is black when you sleep. Between 10pm and 2am is when the body produces a lot, so the earlier to bed, the better.

      (Right now its midnight! What with electricity. computers and the internet, and a job that finished late, its hard to stick to early nights!!)

      EMFs are also said to interrupt melatonin production, so if that were the case, it would be good to turn everything off and put cell phones in airplane mode.

  • Night nurse

    I’ve been a full time night nurse for more than twenty years of my career. I am obese and I can’t help but notice that some of the others nurses are too. Until they realize my contribution to the team, the day staff think I (we) are fat because we must be lazy but I know I am definitely NOT lazy. I am awake during my nights off even if I am awake all day. I am close to retirement. I know there is a link between obesity and breast cancer (as well as ther types of cancer). What can I expect for my retirement in terms of sleep pattern changing back to the ‘norm’ and breast cancer risk?

  • Night nurse

    There seems to be a link between night shift workers and obesity……AND a link between obesity and breast cancer…

  • Night nurse

    How does melatonin factor in?

  • Concernedwoman

    Unfortunately, many of us ate the meat and dairy our parents fed us as adolescents. I am 39 and eating a whole foods plant based diet. But I know that my risk of breast and other cancers are still elevated. Are there any other protective measures that you recommend?