by Valentina Cattero
Abstract
Fennel is a common plant found both in gardens and in the wild countryside around Europe, Asia and North America. It has a long history in the traditional gastronomy and folk medicine of rural communities around the Mediterranean basin, where it is used to flavour dishes and liquors, as well as used to treat an extremely broad variety of diseases since Greek and Roman times. The main constituents found in the plant are essential oil that is responsible for its characteristic aroma and taste. Moreover phenolic and flavonoidal compounds play a major role in its phytochemistry.
The plant has been investigated regarding several properties, antioxidant, anti-ulcer, antimicrobial, antifungal, diuretic and hepatoprotective activity; moreover clinical studies on its effectiveness in treating different conditions such as infant colic, hirsutism (pathological condition of excessive body hairs in parts of the body where usually are not present), dysmenorrhea and premenstrual syndrome have been conducted with positive results. Nevertheless, many sides of the potential of this plant still remain uncovered and would require further research. In general its use as a vegetable of a tea is considered to be very safe.
Photo: ©Valentina Cattero
Botanical
Fennel is a widespread and common plant that everyone has come across at least once in his life in southern Europe; if not the wild fennel, the cultivated one is commonly present in culinary recipes. It is a native of the Mediterranean area that has been naturalized not only throughout all of southern Europe, but also in North America and Asia (Prance and Nesbitt, 2012), where it is very common for example in Kashmiri Pandit and Gujarati cooking in India (Grieve, 1971), the first country producing and exporting fennel (FAO). Botanically speaking fennel is part of the Apiaceae, in which we find carrots, caraway and coriander as well.
Foeniculum vulgar – Köhlers Medicinal Pflanzen 148
The family is also called Umbelliferae, since these herbaceous plants have characteristic inflorescence that resemble an umbrella. Fennel is an herbaceous perennial plant, with erect stems that become hollow with growth. It can grow up to 2.5 m with feathery green-blue leaves ending in filiform feather-like segments. The yellow flowers are grouped in this umbel structures and each one can contain between 20 and 50 tiny flowers. The fruits are small dry brownish thin seeds with an elongated oval shape and distinctive darker stripes on the long side. The whole plant has a distinctive smell and taste that often resembles anise or liquorice.
The botanical name of fennel is Foeniculum vulgare Mill. The fennel used in the kitchen is the enlarged white bulb-like base of the stem joint with the leaf-sheaths of Foeniculum azoricum Mill., which is cultivated in gardens. On the other hand, the pharmaceutically and ethnobotanically most important varieties are from Foeniculum vulgare especially its var. dulce (also called sweet fennel) and Foeniculum vulgare var. vulgare (bitter fennel). These two varieties are impossible differentiate morphologically, not even microscopically, but they differ in taste, since the first one contains more anethole, that yields a sweet taste, while the second one has more fenchone, resulting in a bitter taste (Heinrich et al., 2012). Furthermore, sometimes the wild fennel growing throughout the countryside of the Mediterranean basin is referred as Foeniculum vulgare var. piperitum (C.Presl) Ball.
History and traditional uses: food and medicine
Wild fennel has been used gastronomically and medicinally since ancient times: fennel seeds were discovered in tombs of ancient rulers in Egypt of the III millennium BCE (Bartram, 2013), while the Greek mythology tells in the Prometheus myth that knowledge came to humans in a “fiery coal contained in a fennel stalk” (Griffith, 1983). In Greek the name of fennel is μάραθον (màrathon) or μάλαθρο (málathro), which refers to the famous battle of Marathon (490 BC) against Persians that was fought on a fennel field (MacNeill, 2007). During Pliny’s time in the Roman Empire, snakes were thought to eat fennel in order to restore their eyesight after the skin moult (Albert-Puleo, 1980).
During Greek and Roman times the leaves were widely appreciated as a vegetable, herbal medicine and seasoning (Prance and Nesbitt, 2012), as well as the seeds, which were often added to wine as a flavouring. It was not only used gastronomically, but also in traditional medicine. In Saxons culture it was one of the nine sacred herbs mentioned in the “Nine Herbs Charm”, that is thought to be used to treat the corresponding nine causes of diseases (Banham, 2009). Wild fennel is still crucial in the culture of many populations across Europe and particularly in the life of the rural communities around the Mediterranean basin. It is broadly used in all of southern Italy, from Sicily to Apulia, and in all of Greece. Both leaves and blooms have a culinary use, with the latter common mostly in the tradition of Salento, the southern part of Apulia region. The leaves have to be collected between March and May, while the flowers of course are ready later, in summer between June and September. It is used to aromatize many dishes in both the kitchens of these countries, either raw or cooked, and to make liquors and teas as well.
The leaves are added to many dishes in order to give sweetness and aroma (e.g. fish and meat dishes, pasta, Ντολμαδακια (ntolmadakia), rolled vine leaves filled with rice, pita pies and tzatziki). The blooms, on the other hand, have a peculiar use in Salento; they are called caruselle, preserved in vinegar, then eaten in salad, or as a filling in “pitta di patate” (potato cake) or in focaccia bread.
The uses in popular and local medicine include this plant for various applications, from skin to digestive conditions, to respiratory and nutritional problems (González-Tejero et al., 2008; Maxia et al., 2008; Šarić-Kundalić et al., 2010), but probably it is best known as a diuretic and mild carminative (Heinrich et al., 2012). It is usually prepared as a mild infusion or decoction of the fruits with a little honey for the babies, while for adults a stronger tea or the essential oils would suit.
Phytochemistry
The essential oil is the main component in fennel chemistry and represent the volatile component that gives the unmistakable aroma to the plant. The most important compounds are anethole, fenchone and estragole, which are more abundant in the aerial parts (leaves, flowers, fruits) (ESCOP, 2003; Garg et al., 2009; Heinrich et al., 2012; Rather et al., 2012). The concentration can vary significantly depending on the age of the plant, the geography and the characteristics of the environment in which it is growing (soil, humidity, weather etc.) and, of course, depending on the variety of fennel (Diaaz-Maroto et al., 2006). Indeed, as previously mentioned, the sweet variety contains more anethole, while the bitter one owns its taste to the greater share of fenchone. In addition to essential oils, phenolic and flavonoidal compounds are present in the plant and are thought to play an important role in the prevention of those diseases triggered by oxidative stress (cancer, cardiovascular and neurodegenerative diseases, etc.) (Rather et al, 2012).
Modern accepted uses and pharmacology
The medicinal use of fennel as a herbal medicine is currently accepted and regulated by the European Medicines Agency Committee on Herbal Medicinal Products (HMPC) for the following indications: gastrointestinal complaints (flatulence and bloating conditions), symptoms of the menstrual period (spasms and cramps) and cold symptoms (expectorant to get rid of the excess mucus) (EMEA, 2007a; EMEA, 2007b). The doses and method of administration for all these indications are: 1.5–2.5 g freshly comminuted dried fennel fruits as an infusion in 0.25 L boiling water (brewed for 15 minutes) three times a day for adults and 3–5 g a day in divided doses for children (EMEA, 2007a; EMEA; 2007b). Moreover, the potential of fennel has been investigated regarding several other applications, which follow.
In vitro and animal studies
Antioxidant effects
The antioxidant potential of fennel has been assessed in some detail. The phenolic compounds are thought to be mainly responsible for its antioxidant activity (Ruberto et al., 2000; Parejo et al, 2002; Baliga et al, 2003; Choi and Hwang, 2004; Parejo et al, 2004; Satyanarayana et al., 2004; Marino et al., 2007; Faudale et al., 2008; Garg et al, 2009; Nickavar and Abolhasani, 2009; Ozcan et al., 2009; Mohamad et al., 2011; Rather et al., 2012; Medicines Complete, 2017), although in one in vitro study also essential oils have been hypothesized to play a role in the prevention of oxidative stress related diseases (Shahat et al., 2011). In addition, wild fennel’s higher phenolic and flavonoids content has shown a stronger radical scavenging activity than the medicinal and cultivated one (Faudale et al., 2008). The therapeutic relevance of such effects is uncertain, but it is likely to be relevant for the many health preventive effects of fennel.
Anti-ulcer activity
In animal studies a fennel extract showed a promising protective activity against stomach damages and ulcers (Birdane et al, 2007; Sumbul et al, 2011; Al-Mofleh, 2013). This effect is likely partially linked to its antioxidant activity and thus its phenolic content (Birdane et al, 2007; Sumbul et al, 2011).
Antimicrobial, Antibacterial and Antifungal effects
Several in vitro studies have demonstrated the capability of the essential oils extracted from fennel to inhibit and kill a broad spectrum of microorganisms from bacteria to fungi, such as Staphylococcus aureus, Escherichia coli and Candida albicans (Dadalioǧlu and Evrendilek, 2004; Lo Cantore et al, 2004; Mohsenzadeh, 2007; Gutierrez et al, 2008; Garg et al, 2009; Kaur and Arora, 2010; Pai et al., 2010; Esquivel-Ferriño et al, 2012; Qiu et al, 2012; Piras et al., 2014) as well as the extract, but in lesser extent (Mahady et al, 2005; Kaur and Arora, 2009).
Diuretic effects
Despite the wide and common use of the decoction of fennel seed as a diuretic in the traditional medicine of countless communities in the Mediterranean region, little or no research has been conducted in this direction. Therefore, there isn’t enough scientific evidence to prove the effect of this plant to stimulate urination (Wright et al, 2007).
Hepatoprotective effects
Fennel has been studied for its hepatoprotective properties (Ghanem et al, 2012), but only one animal study has been conducted so far. It suggests that fennel can exert a protective effect against induced damages on the liver (Özbek et al, 2003). Nevertheless, further investigation are needed to draw conclusions.
Clinical evidence
Colic
Fennel has been used for centuries to relieve the colic in infants, and several studies have been conducted in this direction (Blumenthal et al, 1998; Bradley, 2006; Rahimi and Ardekani, 2013; Badgujar et al, 2014). There have been a consistent number of clinical studies in this area, and all of them have shown significant improvement in eliminating the excess gas in the gastrointestinal tract of babies (Alexandrovich et al, 2003; Savino et al, 2005; Perry et al, 2011; Medicines Complete, 2017), which confirms the use of fennel as a mild carminative in traditional medicine. An herbal supplement has been developed, ColiMil®, containing fennel, chamomile and lemon balm and currently can be found on some Continental European markets to treat infantile colic (Savino et al, 2005; Capasso et al, 2007; Savino et al, 2008).
Effect on the menstrual cycle
For centuries fennel has been known as an estrogenic and has been used in traditional medicine to increase milk production in breastfeeding moms, to alleviate pains and cramps during the menstrual period and to facilitate birth (Albert-Puleo, 1980; Sultana et al, 2005; Rather et al, 2012); these properties are probably due to the content in phytoestrogens, compounds synthesized by plant that have a hormone-like activity. One clinical trial has studied the potential of fennel to overcome amenorrhea with a positive outcome: 73% of the 78 women participating in the study experiencing amenorrhea had a substantial cycle when administered fennel in comparison to those assigned placebo (Mohebbi-kian et al, 2014). More importantly, several clinical studies have been designed to prove the effectiveness of fennel to reduce the symptoms of dysmenorrhea, a condition affecting especially young women. Dysmenorrhea is defined as the occurrence of severe and painful cramps during the menstrual cycle, without any evidence of pathologic lesion, and/or uncommon long duration of the period (Amini et al., 2016). In all the studies a significant decrease in pain, cramps, nausea and duration of the menstrual cycle has been shown, indicating that the herbal drug is effective in treating the symptoms of dysmenorrhea (Nahid et al, 2009; Delaram et al, 2011; Omidvar et al, 2012; Ghodsi and Asltoghiri, 2014; Zeraati et al, 2014; Amini et al, 2016). Moreover fennel extract has been found effective in reducing anxiety, depressive, emotional and physical symptoms of pre-menstrual syndrome (Pazoki et al, 2013; Pazoki et al, 2016), especially if combined with aerobic exercise (Pazoki et al., 2016). Finally, there has been one clinical trial testing the potential of fennel in relieving postpartum pains in comparison to ibuprofen in 90 women and fennel was found almost as effective as the medicine and could be a valid alternative for women who don’t want or can’t rely on non-steroidal anti-inflammatories, but more studies are certainly needed (Asti et al., 2011).
Hirsutism
Most probably thanks to its previously cited content in phytoestrogens, fennel has been used in traditional medicine to treat hirsutism (Anjum et al, 2013), that is to say the excessive growth of hairs on certain parts of the face and body, which is often related to a hormonal imbalance. Two clinical studies have been performed with creams at 2% and 3% fennel concentrations, and have substantially decreased the hair thickness (Javidnia et al, 2003; Akha et al, 2014).
Toxicity, risks and interactions
The first risk related to fennel is that it can be mistaken for poison hemlock (Conium maculatum L.) by an inexperienced person or novice to foraging and this plant can lead to death if ingested. For this reason extreme attention has to be paid when collecting it from the wild.
Conium maculatum L. plant (poison hemlock)
Fennel may cause some allergic reaction in the skin and the respiratory tract (Blumenthal and Busse, 1998; Bartram, 2013), but these kinds of reaction are sporadic and in the USA the plant is listed as GRAS, Generally Regarded As Safe (US-FDA). Pure essential oil of fennel (or any other essential oils) should not be administered to infants, due to the risk of problems in respiration (Wichtl, 2012) and general toxicity. The regular and continuous use of the plant has been linked to the appearance of thelarche, the premature development of breast in young girls with no other sign of puberty. This is probably due to its estrogenic activity, since – when the fennel supplementation was stopped – the condition regressed (Türkyılmaz et al, 2008; Okdemir et al, 2014). Moreover, due to its activity on the menstrual cycle (see above) fennel is not recommended to be used during pregnancy.
The main serious concern about fennel is estragole, one of the main component of its essential oil, which has been found to be carcinogen in an animal study (Drinkwater et al., 1976) and following several in vitro studies (Swanson et al, 1979; Swanson et al, 1991; McDonald, 1999; Paini et al, 2010; Rather et al, 2012). Therefore, since the early 2000 the use has been restricted by the European authorities (Opinion of the Scientific Committee on Food on Estragole, 2001; EMEA, 2004). However, more recently question have arisen about the validity of these concerns. In the first instance only studies on the single compound have been carried out and not on the whole plant. This depends not only on the dose of estragole intake, but also on how the molecule acts within the body and is metabolized (Gori et al, 2012; Rather et al, 2012). Moreover, usually fennel supplementation is undertaken short-term only. Therefore, the use should not pose any risk for human health (Gori et al, 2012).
There have been only a few studies investigating the chances of fennel constituents to interact with the metabolism of other drugs, and, even though some of them have found an in vitro inhibition of the enzymes that are responsible for the processing of drugs in our body (CYP3A4 and CYP2D6 in particular) (Usia et al, 2006; Zaidi et al, 2007; Langhammer and Nilsen, 2014), the clinical significance of the findings is still not confirmed. Surely more studies on this point are needed, since herb-herb and herb-drug interactions are one of the main concern nowadays.
Conclusions
Fennel has an extremely broad spectrum of uses, from the culinary and gastronomical one, to the countless applications in traditional medicine. A good number of studies has been conducted on several of its properties, but many aspects still remain unclear or have not been uncovered yet through scientific research and for sure there is still a lot to be explored on the topic. The quality of the studies varies and many claims would need more detailed research.
Many other of the indications for which it is used in the traditional medicine have not been developed and they could be the lead to new findings. Anyway, we can definitely conclude that fennel is a safe herb to use, with reduced risks if taken according to the recommended doses and suggested periods.
Disclaimer
In this essay, we do not intend to advise or recommend herbs for medicinal or health use. This information is for educational purposes only and should not be considered as a recommendation or an endorsement of any particular medical or health treatment. The use of any such product should be based on the appropriate advice of a health care professional or based on the information available in the patient information leaflets (i.e. for THR products). The information provided should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
Valentina Cattero, MSc student (2016 – 2017), Research Cluster ‘Biodiversity and Medicines’ / Centre for Pharmacognosy and Phytotherapy, UCL School of Pharmacy, Univ. London, 29 – 39 Brunswick Sq., London WC1N 1AX
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