The Science to Set the Saga Straight…Hormonal Effects and Essential Oils & Link to March 2018 Top Holistic and Integrative Health Reads







Listen to Part II of my review of clary sage oil in about 7 minutes below.


Listen to this blog in about 8 minutes below.


I just published Part II of my review of clary sage oil on my Healing, Health, and Wellness blog. In this article, I also provided a summary of all my most recent posts relating to the hormonal effects of essential oils. It contains links to an introduction to hormones and essential oils, the debunking of the latest endocrine scare with lavender and tea tree oils, my takeaway points for safe use of essential oils for overall and reproductive health, and more. If you’ve fallen behind, or, just curious, it may be of benefit to you to read it.

As I’ve mentioned previously, the goal of this series of “estrogenic oils” is to examine the research, provide the experts’ interpretations, and state my conclusions based on my own experience and assimilated knowledge of essential oils.

Now, I will continue with the next highlighted essential oil, fennel. Similarly to clary sage oil, first, I’ll give an overview of this essential oil. Then, in a future post, I will focus more on the research relating to its hormonal effects.









A Tasty Review of Fennel Oil

Essential oils have a history of internal application for healing purposes. In fact, many are listed in the European Pharmacopeia. (sourcesourcesourcesource, source) for taking by mouth. If you’ve been following my essential oils blogs for a while, you may remember back when I highlighted the culinary benefits of fennel oil. I used this popular oil as a specific example of the safety of essential oils for ingestion.

Below is an overview of fennel oil, which is important to understand as we consider its synergistic effects on the whole body, not just isolating hormonal studies.

In Part I of my fennel series, I wrote:

Fennel (Foeniculum vulgare) is a biennial plant with yellow flowers and feathery leaves. This medicinal and aromatic herb belongs to the Apiaceae (Umbelliferaceae) family, which is also known as the celery, carrot, or parsley family. Its origins are from the Mediterranean, but it is widely cultivated worldwide. (1, 2, 3, 4)

The composition of pharmacological grade fennel oil is standardized in the European Pharmacopoeia to not less than: 60% anethole, 15% fenchone and a maximum of 5% estragole with the seed containing not less than 4% of the total volatile oils. The official fennel oil is Foeniculum vulgare (bitter fennel) versus Foeniculum dulce (sweet fennel). Anethole is responsible for sweet taste; whereas fenchone, is bitter.

I then discussed the German E Commission guidelines for fennel and highlighted their internal usage instructions as evidence of safety with proper use (see below). Fennel oil’s indications include:

  • Digestive and respiratory system soothing
  • Potent microbe inhibition
  • Antioxidant and a flavoring agent

In Part II of my fennel series, I discussed in vitro, in vivo, and human trials with fennel oil. I also highlighted some hormonal effects found in petri dishes (which we are cautious about interpretation) and rodents (again, caution noted). From these studies, fennel oil was found to:

  • Protect rats’ livers
  • Calm mice’s brains
  • Support healthy breast cells in petri dishes
  • Promote healthy milk production in pregnant women (HUMANS) (source, source, source, source)
  • Provide antispasmodic action for modulating uncomfortable uterine contractions in pre-menstrual rodents (I guess rats get PMS too!)
  • Selectively cytotoxic in cancer cell lines







Back to Safety First: The Safe Use of Fennel Oil and the Estragole Debate

In my blog on the Five Safety and Usage Precautions of Fennel Oil (specifically),  I reviewed the importance of:

  • Proper Dosage
  • Quality of the essential oil
  • Taking the therapeutic essential oil vs. the isolated constituents
  • The estragole debate

All of the above factors, except for the estragole debate, you can access in the resource section of safety here.

What’s the big deal about estragole? Fennel is one essential oil that contains this compound, and some have considered it “toxic.” In this blog, I wrote the caveats behind declaring this substance harmful. Some of these points may sound familiar…

Not considering the differences between an isolate and the metabolic pathways of rodents vs. humans may be why one of fennel’s constituents, estragole, was initially deemed toxic. However, when further explored for human consumption, it was found to not pose a risk at intended dosages.
According to the [2005] 
EMA (European Medicine’s Agency):

…Exposure to [estragole] resulting from consumption of herbal medicinal products (short time use in adults at recommended posology) does not pose a significant cancer risk. Nevertheless, further studies are needed to define both the nature and implications of the dose- response curve in rats at low levels of exposure to [estragole]. In the meantime exposure of [estragole] to sensitive groups such as young children, pregnant and breastfeeding women should be minimised.” *

*Important note: The studies were using straight estragole and not reporting on the internal use of fennel oil, which was reviewed here. (Another less important note, minimize is spelled differently across seas, minimise ;)).

In an excellent 2012 comprehensive review article in Evidence-based Complementary and Alternative Medicine, the authors summarized the mechanisms of action of fennel’s constituents and the differences in their assimilation and biotransformation in humans versus rodents. They also discussed the importance of considering the whole “decoction.”  The authors stated:

Consideration of these issues (dose, administration form, and differences in metabolism between species) raises doubts about the conclusion that fennel seed can be “reasonably anticipated to be a human carcinogen” [44], It is clear that human and animal metabolism cannot be directly compared but we think data should deserve attention.

They concluded (bold emphasis mine):

In all of the animal studies reviewed, isolated, purified estragole was used. Thus the findings give a toxicological profile of this only molecule and not the profile risk of the entire decoction. In humans estragole usually enters the body as a component of fennel tea, or as a food that has been seasoned with herb that contains many other substance like nevadensin, epigallocatechine, other flavonoids, and anethole, that have a protective role and so counterbalance to the possible effect of pure estragole. In this context estragole occurs in the form of an extremely complex phytochemical mixture. If data about single constituent in vivo can be used as basis for statements about a herb, then data about other constituents should also be fully considered, because we think it is the only way to establish definitively if a substance is dangerous or not; and if it is a substance used from many years and in particular subsets of consumers or patients epidemiological data, when available, can help in establishing, together with the real mode of use, the effective risk for consumers. (source)

In a 2016 30-day (HUMAN) study with predominately female IBS (irritable bowel syndrome) patients, the effect of a combination of curcumin with fennel oil was studied in relationship to improvements in quality of life and symptoms. The authors reported that this combination “was safe, well-tolerated and induced symptom relief in patients with IBS.” (Note, study funding may have influenced result.)

This weekend, I’ll review what we’ve learned about fennel in my oily weekend tip and how I use it personally and in my clinic. Then, I’ll continue on with a few studies that examine its’ hormonal effects, or lack-there-of, in a later post.

Now, I want to hear from you…







Have you used fennel oil for hormonal health or any of the uses above?

What did you notice with using fennel oil?


Click here for the March 2018 Top Holistic and Integrative Health Reads.


This material is for information purposes only and is not intended to diagnose, treat, or prescribe for any illness. You should check with your doctor regarding implementing any new strategies into your wellness regime. These statements have not been evaluated by the FDA. (Affiliation link.)

Disclaimer: This information is applicable ONLY for therapeutic quality essential oils. This information DOES NOT apply to essential oils that have not been tested for purity and standardized constituents. There is no quality control in the United States, and oils labeled as “100% pure” need only to contain 5% of the actual oil. The rest of the bottle can be filled with fillers and sometimes toxic ingredients that can irritate the skin. The studies are not based solely on a specific brand of an essential oil, unless stated. Please read the full study for more information.

Thanks Pixabay and iStock purchases.