Circadian rhythms and breast cancer

Over the course of human evolution, diets varied widely over time, seasons, geography, etc., ie, we can obviously thrive on many different dietary patterns… but the light/dark cycle was there the entire time.  Why is this not the most important talking/debating point?  Why do people think humans need one particular diet but can ignore circadian rhythms?

Because everyone’s still fussing about carbz and what we are “designed to eat”


see also: “Lights Out!” by T.S. Wiley



Here is a brief summary of how this studies was done (Ha et al., 2016): breed a mouse that is highly susceptible to metastatic breast cancer to one with low susceptibility.  Their progeny will have a range in susceptibility.  Then genotype the mice to find correlations between presence/absence of certain SNPs and the degree of susceptibility.  In this case, they found Bmal2.  Then they transfected another line of mice with the protective version of Bmal2 and checked to see if it affected susceptibility.  In this case, it did, and knocking it out had the expected (opposite) effect.




Lastly, see if the relationship holds true in actual human patients.  In this case, it did.

They found a strong association of one version of the circadian gene Bmal2 with ER- breast cancer “disease-free survival.”  In other words, it correlated with breast cancer that didn’t metastasize.  In many cancers, it’s the metastasis, not the primary tumor, that is poor for prognosis.



Some stats: 5-year survival for non-metastatic breast cancer is almost 100% whereas that for metastatic breast cancer is only 26%.  That’s why this is hugely important.  Now we know one factor that differentiates the two: circadian arrhythmia.  The next step, I figure, is to determine exactly how.  This is what the researchers think is going on in this case:




“ARNTL2 (Bmal2) levels significantly influence mammary tumor metastasis.”





This isn’t the first study to identify a link between Bmal2 and tumor metastasis (eg, see Brady et al., 2016).



And many others have linked circadian arrhythmia in general and breast cancers:

Circadian Medicine

Circadian Physiology

The incidence of breast cancer among female flight attendants (Liu et al., 2016)

Circadian clocks and breast cancer (Blakeman et al., 2016)

Shedding light on the role of circadian disruption in breast cancer etiology (Lagiou 2016)

Light at night and breast cancer incidence in Connecticut: an ecological study of age group effects (Portnav et al., 2016)




Over the course of human evolution, diets varied widely over time, seasons, geography, etc., ie, we can obviously thrive on many different dietary patterns… but the light/dark cycle was there the entire time.

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  • TechnoTriticale

    Even a generous shift differential does not compensate for the hazards of a solar-asynchronous lifestyle. Right now this is primarily appreciated by some circadian and cancer researchers, and by those of us otherwise paying attention. But we can expect the broader community of healthcare professionals to be among the next to wake up to it, so to speak, perhaps starting with oncologists.

    This presents a huge problem for healthcare generally, and specifically for certain legacy practices, such as the nutso schedules common in MD residency. Emergency responders won’t be far behind in figuring it out.

    What positions these communities will take, and can indeed be done about this, for services that must be 24×7, is not at all clear.

    Eventually it might be tele-medical avatars operated by humans residing where the sun is shinning at the moment.

  • Eve

    Great timing! I just ordered a pair of reading glasses today with a blue light filter.

    • oh, cool. What brand?

      • Eve

        They’re prescription glasses, but it’s the first time that I’ve encountered an optician who offered this feature.

  • Colin Champ

    Bill, great article. I always coughed it up to disrupted melatonin production, therefore losing its anti-inflammatory and anti-cancer benefits, especially with breast cancer. It is interesting to see the emergence of some of the other factors. There is some data showing that cancer cells may be more susceptible to radiation therapy based on the time of day that patients receive treatment. We have lot’s to learn…