An easily controllable risk-factor for breast/prostate cancers that few people know about


Interesting that breast cancer is far more common in industrialized countries than in 3rd world countries, and far more common in cities than in less densely populated regions. Women in certain professions (like nursing) are at greater risk. But this risk factor is easily controllable, if you know about it.

We probably all know someone who has either breast or prostate cancer, as they are the most commonly diagnosed cancers in females and males respectively. Although family history is an uncontrollable risk factor in both cancers, there are many other risk factors that we can control, and may determine whether or not cancer develops.

There is more and more evidence linking artificial evening and night-time light to the growth of cancer cells. The risk of breast cancer is five times higher in industrial nations lit with electric lights than in the underdeveloped countries of the world.

A study done in 2001 by the Fred Hutchison Cancer Research Centre in Seattle found that women who worked the graveyard shift had a 60% greater risk of getting breast cancer than those that did not.

Women that regularly sleep nine hours a night have less than a third the cancer rates of those that regularly sleep seven, according to a Finnish study published in Cancer Research in 2005. Interestingly, it does not seem to be the sleep that matters, but rather the hours spent in darkness.

Melatonin is the immune hormone that is secreted in darkness. Melatonin is supposed to be at its peak between 1 and 2am, and if we are still up with the lights on at that time, very little or no melatonin will be secreted.

Melatonin seems to stop cancer cells cold, and puts them to sleep for the night. Breast cancer grows in the presence of light, because of the absence of melatonin.

In a very interesting study published in Dec. of 2005 and funded by the NIH, rats that were implanted with human breast cancer were either given melatonin rich blood from women that had been in complete darkness for 2 hours, or blood from women that were exposed to bright light.

The tumors in the rats that were given blood with the lowest melatonin concentrations (the blood that came from women exposed to light) multiplied the fastest.

Melatonin seems to block the ability of cancer cells to metabolize linoleic acid, the omega 6 fatty acid that is found in vegetable oils, thereby preventing the cancer cells from dividing. Melatonin also seems to have a role in controlling the excess production of estrogen and estradiol, another factor in the growth of breast cancer.

The recent statistics that have come out have indicated a big drop in rates of breast cancer, and it is believed that this drop was due to the reduced use of hormone replacement therapy in 2002, solidifying the theory that high estrogen levels play a roll in developing breast and also cervical cancer.

Estrogen dominance may also occur as a result of chronically high insulin levels, so decrease your sugar and starchy carbohydrates if there is breast cancer in your family, and get your dark time, as melatonin also seems to have a role in controlling the excess production of estrogen and estradiol.

It is interesting to note that decreased melatonin levels due to too little dark time results in increased levels of cortisol, which in turn translates into higher insulin levels, which leads to problems with type 2 diabetes and heart disease in addition to cancer.

So, the bottom line is that getting enough hours in complete darkness is vital to hormone regulation, which is vital to optimal health.

Although there is less research with regard to the protective effects of melatonin on prostate cancer, the research that is there certainly does support the hypothesis, and more research is ongoing. Melatonin seems to be protective in some other cancers as well, such as skin cancer.

The message for us all? Get to bed early enough that you will get 9 hours of dark time, and use a red night light if you need to use the bathroom in the night. If going to bed early on a regular basis is impossible for you, get black-out drapes and make sure you get you can sleep in long enough in the morning to get your nine hours of dark time.

Another super useful trick is to put on your sun glasses at 10pm – use yellow lenses that cut out all blue light, as it is the blue light that is problematic. This would be a great strategy if you are working night shifts. It may also make it easier to fall asleep when you finally do make it to bed.

Reducing your consumption of omega 6 fatty acids – vegetable oils like soy, canola, sunflower etc, grain-fed beef etc., and increase omega 3 intake from fish oils in order to improve the omega 6 to omega 3 ratio may also assist in reducing your risk of getting cancer.

Related tips:
Light Pollution Messes With Your Hormones
Vegetable Oils – Friend or Foe?
Essential Fats – Omega 3 to Omega 6 Ratio

Proietti S, et al. Molecular mechanisms of melatonin’s inhibitory actions on breast cancers. Cell Mol Life Sci. 2012 Sep 25.

Alvarez-García V et al. Regulation of vascular endothelial growth factor by melatonin in human breast cancer cells. J Pineal Res. 2012 Aug 16. doi: 10.1111/jpi.12007.

Davis S, et al. Night shift work and hormone levels in women. Cancer Epidemiol Biomarkers Prev. 2012 Apr;21(4):609-18. Epub 2012 Feb 7.

Davis, Scot et al. Light at Night and Working the Graveyard Shift Linked to Increased Risk of Breast Cancer Journal of the National Cancer Institute October 2001

Blask, David, MD, PhD et al. Melatonin-Depleted Blood from Pre-Menopausal Women Exposed to Light at Night Stimulates Human Breast Cancer Xenografts in Nude Rats Cancer Research 65, 11174-11184, Dec. 1,  2005.

Verkasalo, P. et al. Sleep Duration and Breast Cancer: A Prospective Cohort Study Cancer Research 65, 9595-9600, Oct. 15, 2005.

Harder, Ben. Bright Lights, Big Cancer Science News Online Jan. 7, 2006.

Sainz. RM et al. Melatonin reduces prostate cancer cell growth leading to neuroendocrine differentiation via a receptor and PKA independent mechanism Prostate 63(1) 29-43, April 1, 2005.

Moretti RM et al. Antiproliferative action of Melatonin on human prostate cancer LNCaP cells Oncol Rep 2000 7(2):347-351.

Fraschini F. et al. Melatonin involvement in immunity and cancer Biol Signals Recept 1998, 7(1): 61-72.


  1. One Green Earth’s Blog » Blog Archive » Go to bed early- reduce cancer - reduce energy waste - stay healthy - MELATONIN said,

    February 3, 2009 @ 10:44 am

    […] Thanks to […]

  2. Lesley Freeman said,

    November 4, 2009 @ 6:02 am

    I am not sure what you mean about the omega oil and soya reducing I thought omega 6 was good for you and soya. I take a soya I take a supplement called Fitoladius 80,I was recommended to take this instead of hrt.I take Melatonin every night

  3. Alcoholism Treatment : said,

    October 26, 2010 @ 8:17 am

    breast cancer is of course easy to diagnose early and very easy to treat if you catch it early;;-

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    December 2, 2011 @ 11:16 pm

    I do not know if it’s just me or if everyone else encountering issues with your blog. It looks like some of the written text in your posts are running off the screen. Can somebody else please comment and let me know if this is happening to them too? This might be a problem with my internet browser because I’ve had this happen previously. Appreciate it

  5. Liz said,

    November 4, 2012 @ 2:16 pm

    Very interesting idea, definitely food for thought. Not to mention, inspiration to ensure quality sleep habits.

    I have just one detractor and that is early in your article where you mention genetic risk factors. Researchers like Dr. Bruce Lipton (The Biology of Belief) and Dr. Gabor Maté (When the Body Says No: The Cost of Hidden Stress) are bringing to light the reality that it’s not our genes that determine our future health, it’s our lifestyle and choices, both physical (food, sleep, etc.) and especially emotional (stress levels, emotional coping, etc.).

    The internal environment in which our bodies live is just as important as the external, perhaps even more so.

  6. Vreni said,

    November 3, 2013 @ 4:51 pm

    Hi Liz – I agree. I have Dr. Mate’s book on my Kindle now, and it is next on my reading list.



  7. Rebecca Cody said,

    November 3, 2013 @ 3:59 pm


    Thanks for your informative articles. I always learn something from you.

    One reader above commented on finding breast cancer early and how successful treating it is. However, while this can be true, there are many variations in breast cancers. Thousands of women die from the disease now (I think about 500,000 yearly, but don’t quote me), and some die from treatments, or get other cancers down the road that were caused by toxic treatments. My breast was clear of lumps in the spring of 2009, but had a huge triple negative tumor a year later.

    People tend to think that ALL breast cancers are caused by too much estrogen or occasionally too much progesterone. However, triple negative breast cancer, which is one of the most aggressive and fatal types, is not connected with female hormones at all. It grows very quickly and has a poor track record for treatment. The two women I’ve known who had it lived less than a year after diagnosis.

    When I saw a new oncologist at Seattle Cancer Care Alliance a few months ago, after semi-successful chemo treatments and then a mastectomy, she read my chart notes, then looked at me and said, “We don’t see many women with your diagnosis three years later.”

    “No, I’m supposed to be dead by now, right?”

    She agreed. Yet, in the final analysis, she wanted me to have more of the kinds of treatments that have not worked for her other patients. I told my husband later, “Instead of recommending I do what hasn’t worked for others with my diagnosis, she should be asking me what I have been doing to remain healthy otherwise, and even thriving.

    I appreciate your suggestion for using yellow sunglasses (shooting glasses). I’ve been a night owl all my life and can seldom sleep before midnight. I think I’ll give them a try.

    I realize I haven’t slept in a truly dark room for decades. I keep wanting it darker but my husband keeps opening the blinds a bit to let in light from back yard lights. He just doesn’t get it. Maybe I need to move into the guest room!

  8. Vreni said,

    November 3, 2013 @ 4:50 pm

    Hi Rebecca,

    I totally agree with you that she should be asking you what you are doing right instead of telling you to try a treatment that has not been successful for her other patients. I think that is one of the biggest problems with chronic disease. Instead of studying the people that are healthy to find out what they are doing right, we study the sick …

    Sounds like you have had a heck of a journey, but are clearly doing something right. The glasses are a cheap and easy solution. Maybe you can put red cellophane on your window, so if your husband opens the drapes the light won’t be as harmful to you? I use a red light at night if I have to get up – the kind one wears over the forehead that one can get for hiking at REI or MEC. That way I don’t need to turn on any of the overhead lights and shut down melatonin.

    Wishing you the best of health,


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