Does Tamoxifen Timing Matter?

As a naturopathic doctor working with many breast cancer survivors who are on hormone therapies (like tamoxifen, letrozole, anastrozole, etc) there are a few things I help my patients and clients with including:

• natural strategies to help decrease side effects of treatments (ie hot flashes, bone pain, sleep issues, osteoporosis, etc)
• stacking strategies to help boost prevention (this is such an important time to do this - when you're already on therapies meant to help lower recurrence risks)
• ways to help boost how these therapies work (this includes avoiding things that could potentially interfere with how they work ie.grapefruit)

So this finding is exciting...

New research came out this year pointing to a potentially easy way to help boost how tamoxifen works.

 What this research found:

1. Taking tamoxifen in the evening (ie. 6pm-11:59pm) seemed to be associated with improved disease free survival (or time period without recurrence) for those with high risk hormone positive/HER2 negative breast cancers rather than taking it in the morning or afternoon.
2. This association with timing was not seen in those taking aromatase inhibitors (ie. letrozole, anastrozole, exemestane) - meaning perhaps timing was not critical for these therapies like it appeared to be with tamoxifen.

While we're not yet sure what the reason is behind this finding - other research has pointed to the fact that circadian rhythm and specifically melatonin levels (the sleep hormone produced at night) may be behind this timing benefit.

In fact, years earlier, an animal study on rats showed that melatonin may be important in helping turn off pathways that could cause resistance and prevent tamoxifen from working optimally. 

In this study, they found light/dark signalling to be important for how much melatonin was produced. 

Complete darkness at night was found to help the body produce more melatonin.

What was interesting was how little light it can take to possibly reduce or suppress the body's production of melatonin. 

Even dim light exposure at night equivalent to light filtering under the door (surprisingly very small amounts of light) was seen to impact how much melatonin was produced. 

So much so that the rats exposed to dim light at night were producing low to undetectable levels of melatonin throughout the day while the rats exposed to pitch black produced 70-fold higher melatonin at it's highest peak during the night than during the day . 

In this study they concluded that "in the presence of the endogenous nocturnal melatonin signal or in response to exposure to melatonin at night under dLEN conditions, tumor latency-to-onset was prolonged while tamoxifen resistance was negated, resulting in tumor regression." (2)

In plain words...both melatonin produced in pitch black conditions or melatonin supplementation under dim light conditions may help prevent tamoxifen resistance and boost anti cancer impacts.

What this means: melatonin supplementation in dim lighting conditions or complete darkness for at least 8 hours (whether or not people were sleeping) may be beneficial to hone in on melatonin's potential benefits.  One of these benefits being its possible positive impact on tamoxifen.

Bottom line to these studies...

While more research is needed and recommendations have not yet changed - taking tamoxifen in the evening may be a really easy but effective way to help boost how well tamoxifen works!

Medical disclaimer: this is for educational purposes only - please speak to your healthcare practitioner before you change or start anything new. 

If you're on or will be on hormone therapies and want to learn about how they work, how to boost the way they work, natural ways to help decrease side effects and boost your prevention strategies...

the 3 Day Breast Cancer Thrivers Masterclass recordings are available on-demand.

Click HERE to find out more and access.

Sources:

1. Giacchetti, S et al. (2023). Influence of hormone therapy timing intake on disease free survival (DFS) for patients with high-risk early breast cancer: Results of the UCBG-UNIRAD phase III randomized trial. Journal of Clinical Oncology. 41.546546.10.1200/JCO.2023.41.16_suppl.546.
2. Dauchy, R. T. et al. Circadian and melatonin disruption by exposure to light at night drives intrinsic resistance to tamoxifen therapy in breast cancer. Cancer Res. 74,1–12 (2014).

3. Lazowski A. Breast Cancer drug's effectiveness improved by sleeping in dark. CBC News. Last updated: Jul 31 2014.