The Oestrogenic Properties of Fennel

Premature  thelarche is defined as isolated breast development with no other clinical signs of sexual maturation  in girls before the age of 8 years. The mechanism is unknown, although increased oestrogen levels can be detected in the serum. A Turkish study describes 4 cases of premature thelarche apparently linked to the long-term consumption of fennel tea.1

The 4 cases were observed between January 2001 and December 2007 in a paediatric department in Ankara. The first case was a 5-month-old infant girl with premature thelarche and elevated  oestradiol. Around the same time a 65-year-old postmenopausal woman was under investigation because her menstrual  cycle had recommenced. Her history revealed  the long-term consumption of fennel tea. This prompted  the authors to search for a link between fennel and the thelarche case and in 3 other subsequent cases (aged 3 to 5 years). All 4 girls had been given fennel tea 2 to 3 times a day for several months to eliminate colic. Physical and genital examination  of the girls were unremarkable.  However, serum oestradiol levels were 15 to 20 times higher than normal for their ages. After the fennel tea was stopped the premature thelarche resolved within 3 to 6 months and oestradiol levels returned  to normal.

Comment

The oestrogenic properties of fennel have been well- described in experimental models.2  This is presumably due to the anethole  content of the essential  oil, but other components  could be active. However, only recently has it been realised that the oestrogenic activity of fennel might be sufficiently strong to have an impact on human health. In a 2003 trial, topical use of a fennel cream successfully treated  idiopathic hirsutism in female patients3 (see e-Monitor No. 1 May

2004) and now there are these cases of premature thelarche. Perhaps the use of fennel tea as a galactagogue  also reflects an oestrogenic activity. Of particular interest is the observation that fennel appeared to increase oestradiol levels in the girls in a situation of absent  ovulation. This suggests that fennel might be valuable for menopausal  symptoms.

 From a safety perspective,  prolonged intake of fennel should be avoided by boys and girls. Clinicians should also be watchful for potential oestrogenic side effects from the use of this herb in either sex. 

REFERENCES

1     Turkyilmaz Z, Karabulut R, Sonmez K et al. J Ped Surg 2008;

43(11): 2109-2111

2     Mills S, Bone KM. Principles & Practice  of Phytotherapy: Modern

Herbal Medicine. Churchill Livingstone, Edinburgh, 2000, p 380.

3     Javidnia K, Dastgheib L, Mohammadi Samani S et al.

Phytomedicine 2003; 10(6-7): 455-458