Melatonin’s Anti-Cancer Effect | In Honor of Breast Cancer Awareness

Melatonin’s Anti-Cancer Effect | In Honor of Breast Cancer Awareness


This year, a fascinating paper was published that summarizes 10 ways that melatonin produces its anti-cancer effects.

anti-proliferative effects

induction of apoptosis

modulation of the immune system

metabolic effects

anti-angiogenic activity

anti-metastatic effects

anti-estrogenic effects

inhibition of telomerase activity

anti-oxidant activity

regulation of genomic stability

Melatonin has anti-estrogenic effects that can help with estrogen related breast cancer, endometriosis, adenomyosis and fibroids. 

The anti-cancer effects of melatonin have been studied extensively in hormone-dependent breast cancer, in particular regarding estrogen. Melatonin is seen to interfere with the following:

  1. The activation of the estrogen receptor.  It is considered to be a selective estrogen receptor modulator (SERM), that decreases both the expression of estrogen receptors alpha (ERα), and the ability of ERα to bind to DNA
  2. The invasiveness of breast cancer cells, reducing the risk of metastasis
  3. In the production and metabolism of estrogen. Melatonin inhibits the enzymes involved in the synthesis of estrogen, thus leads to lower levels of estrogens. It is considered to be a selective estrogen enzyme modulator. 
  4. Melatonin is also seen to be involved in the metabolism of estrogen, transforming estradiol into its inactive estrogen sulphate/sulfate form. This is another example of SEEM activity.

Melatonin is, as far as is known, the only molecule that has both SERM and SEEM properties. This double mechanism of anti-estrogenic effects, plus its invasiveness effects yields melatonin’s unique advantages for the treatment of hormone positive breast cancer.

These anti-estrogen effects may also important beyond breast cancer in estrogen dominance and other conditions associated with estrogen imbalances. 

Many observational studies have looked at whether low melatonin levels are associated with increased risk of breast cancer. In a study on 3,699 post-menopausal women [2], the results show that those with the highest levels of melatonin (from urine assessment)  have a 44% reduced risk of invasive BC compared to those with lowest levels. This association was even stronger (62%) in those who had never smoked or were past smokers. Two other large studies showed similar results. [3,4].

Women working night shifts are also shown to have higher rates of breast cancer. Studies have shown that these women have lower (approx 50%) melatonin levels. The reduction in peak melatonin levels was even shown to correlate directly with the size of tumors in these women. 

There are many scientific studies that indicate melatonin may enhance the effects of some of the chemotherapy medications used to treat breast cancer. In one study, women whose tumors did not respond well to tamoxifen opted to take melatonin and found there was a low percentage of those who experienced the shrinkage of their tumors.

Sleep problems can affect our quality of life. If you're having trouble sleeping, especially during or after breast cancer treatments, you may need to discuss this with your doctor.

Instead of opting for prescription drugs, ask your oncologist if melatonin might be beneficial for you.

After reading the information contained in this article published by the Journal of Pineal Research, some women decided to continue taking melatonin for the rest of their life as part of an alternative healing therapy regimen for breast cancer.

The present study shows that melatonin prevents, within the first cell cycle, the estradiol-induced growth of synchronized MCF7 breast cancer cells. By using nuclear extracts of these cells, they examined the binding of estradiol-estrogen receptor complexes to estrogen-responsive elements and found that the addition of estradiol to whole cells activates the binding of the estrogen receptor to DNA whereas melatonin blocks this interaction. By contrast, melatonin neither affects the binding of estradiol to its receptor nor the receptor nuclear localization. Moreover, it also shows that addition of estradiol to nuclear extracts stimulates the binding of estrogen receptor to DNA, but this activation is also prevented by melatonin. The inhibitory effect caused by melatonin is saturable at nano molar concentrations and does not appear to be mediated by RZR nuclear receptors. The effect is also specific, since indol derivatives do not cause significant inhibition. Furthermore, melatonin does not interact with the estrogen receptor in the absence of estradiol. Together, these results demonstrate that melatonin interferes with the activation of estrogen receptor by estradiol. The effect of melatonin suggests the presence of a receptor that, upon melatonin addition, destabilizes the binding of the estradiol-estrogen receptor complex to the estrogen responsive element.

We’ve looked at some studies that showed significant effects of melatonin on cancer and quality of life, but how does melatonin achieve this? There are several different mechanisms, but today we will focus on just one: melatonin’s anti-estrogenic effects. This might be important for breast cancer (BC) and other hormonal imbalances. Since Melatonin is also classified as a cytotoxin, or a substance that has a toxic effect on certain cells, Melatonin acts a tumor suppressor.

Here are a few ways that Melatonin may prove to be a powerful ally for you in protecting your health:

  1. Melatonin puts Breast Cancer cells to sleep.

 David E. Blask, MD, PhD, a widely acclaimed expert in cancer biology demonstrated that night time melatonin blood levels directly suppressed human Breast Cancer cell growth.

He found that Melatonin put Breast Cancer cells to sleep and slowed Breast Cancer growth by 70%

According to Dr. Blask, “Nighttime Melatonin is a relevant anticancer signal to human Breast Cancers. Ninety percent of human Breast Cancers have specific receptors for this signal.”

When Blask’s team exposed laboratory mice with human Breast Cancers cells to constant light, the breast tumor growth dramatically increased.

   2. Melatonin protects from Estrogen overdose

There is a new buzz word in the environment called “Xeno-estrogens”. Xeno-estrogens are chemicals that actually mimic estrogen in the body. Persistently high levels of estrogen have been associated with an increased risk of Breast Cancer.

Examples of Xeno-estrogens are insecticides, pesticides, food preservatives such as BHA, hormones injected into meats and dairy cows, plastics, parabens in skin care products, 4 MBC in sunscreens, and the list goes on…..

3. Melatonin counteracts the effect of estrogen on Breast Cancer cell growth

4. Melatonin has an anti-carcinogenic role in inhibiting cancer cell growth and in reducing oxidative stress.

5. For women who choose conventional medical therapies, Melatonin is a suitable treatment for reducing the side effects associated with chemotherapy and radiation.

6. Melatonin causes cancer cells to die.  

7. Melatonin is a powerful anti-oxidant with immune enhancing properties. Melatonin also reduced the risk of death in cancer patients in a study conducted in Ontario Canada.

Since Melatonin production peaks in the darkness, make sure that your bedroom is completely light free.

Even a small light can disturb melatonin production. Also, clear out the electronic gadgets from your bedroom since EMF’s have a strong impact on reducing the effectiveness of Melatonin.  This includes televisions, phones laptops, internet devices, etc.

For women that are trying to be proactive with prevention or are on a Breast Cancer healing journey, you may want to consider getting your Melatonin levels checked. This simple test can determine how deficient you may be and what you can do to increase the production of this vital cytotoxic hormone.

Since Melatonin is such a powerful Breast Cancer inhibitor, make sure it is part of your protocol so that you can not only enjoy a restful sleep, but you can also have the peace of mind that Melatonin is hard at work for you.


Concerning BC, studies show that:

low levels of melatonin are a risk factor for BC

there is an inverse relationship between melatonin levels and tumor size (i.e., the lower the peak level, the larger the tumor)

concurrent supplemental melatonin can improve chemotherapy outcomes and reduce side effects in BC

melatonin has effects on both estrogen receptors and estrogen production

Considering melatonin has other anti-cancer mechanisms, such as anti-oxidant, immune-modulating, anti-inflammatory, etc., in addition to its anti-estrogen effects suggests that supplemental melatonin may be of use for BC patients. This seems to be indicated for both prevention and for combined treatment with chemotherapy and radiotherapy. While further definitive trials are needed, melatonin has been demonstrated to be nontoxic, and its benefits on sleep are also important for cancer patients. 

What works for one person, might not work for you. And results from clinical trials come up with statistics, and you aren’t a statistic. If you decide you want to add melatonin to your regimen, try working with a health care provider; if you have cancer, make sure you tell your oncologist. 


  1. Cardinali et al., 2016. Melatonin-Induced Oncostasis, Mechanisms and Clinical 

Relevance. J. Integr. Oncol., S1: 006.

  1. Schernhammer ES, Berrino F, Krogh V, et al. 2008. Urinary 6-sulfatoxymelatonin levels and risk of breast cancer in postmenopausal women. J Natl Cancer Inst. 100(12):898-905.
  2. Schernhammer ES, Hankinson SE. 2005. Urinary melatonin levels and breast cancer risk. J Natl Cancer Inst. 97(14):1084-1087.
  3.  Schernhammer ES, Hankinson SE. 2009. Urinary melatonin levels and postmenopausal breast cancer risk in the Nurses’ Health Study cohort. Cancer Epidemiol Biomarkers Prev. 18(1):74-79.