Every month after menstruation the body begins to rebuild oestrogen levels in the form of oestradiol (the active form of oestrogen). Some oestradiol is converted to a weaker oestrogen called oestrone.  Oestradiol and oestrone are then secreted into the bloodstream and travel to oestrogen sensitive cells to stimulate cell growth.  Peak oestrogen levels are found just prior to ovulation and then falls just before menstruation begins.

Oestrogens are made from progesterone and/ or androgens in the ovarian cells.  After menopause, oestrogens are converted from the adrenal producing androgens, primarily in body fat.  Oestrogen and progesterone are both antagonistic and yet sensitise receptors for the other.  Progesterone has a balancing effect on excessive oestrogen.

Sources of oestrogen

  • ovaries, adrenals and adipose tissue
  • Enterohepatic production (aromatisation of androgens to oestrone)
  • Exogenous (xenoestrogens from the environment)

Oestrogen exhibits sustaining effects on the female reproductive system, it is a hormone which is produced in the ovaries and signalled by the pituitary gland.  Oestrogen is the dominant female hormone and its functions are:

  • Secondary Sexual Characteristics
  • Blood cholesterol
  • Moderate levels modulate GnRH
  • Promotes growth of reproductive tissues, bone and cartilage, epithelial linings (uterus, fallopian tubes and vagina)
  • Increases cervical mucus (clear)
  • Vasodilation
  • Antiatherosclerotic
  • Feminine body proportion
  • More fluid sebaceous secretion (antiacne)
  • Increases fluid retention
  • Endometrial proliferation
  • Secondary sexual characteristics
  • Acidity in the vagina
  • Control fluid and electrolyte balance
  • Stimulates mucous secretion
  • Increase protein anabolism (synergistic with growth hormone)

Many female health problems and symptoms occur due to hormone imbalance, typically oestrogen dominance.  Oestrogen dominance or progesterone deficiency occurs in a woman where there is a high oestrogen to progesterone ratio.  Symptoms of this hormonal imbalance are many and include:

  • tenderness and fibrocystic breasts
  • tendency for increased body fat
  • increased blood pressure
  • thyroid hormone imbalances
  • decreased sex drive
  • decreased blood sugar control
  • Zinc depletion and copper retention
  • increased risk of endometrial, breast, and ovarian cancers
  • impaired liver and gall bladder function
  • increases incidence and growth of fibroids
  • hair loss and facial hair
  • impaired immunity
  • migraines
  • miscarriages
  • pre-menstrual symptoms, PCOS, Endometriosis, fibroids and PMDD
  • increased blood clotting


  • Occurs in the Follicular phase of the menstrual cycle
  • Long cycle
  • Scanty flow
  • Missed cycle (amenorrhea)
  • Reduced ovulation
  • Later menarche


  • Luteal phase of cycle
  • Short cycle
  • Heavy bleeding
  • Dysmenorrhea (painful menstruation)
  • Reduced Progesterone
  • Early menarche
  • PMS, Endometriosis, cyclic breast disorders, fibroids, risk of Oestrogen dependant cancers

Oestrogen has positive effects on the cardiovascular system, bones, brain, skin as well as reproductive organs. The issues experienced at menopause such as memory loss, osteoporosis and vaginal dryness validates the importance of maintaining optimal oestrogen levels. However, if you have too much oestrogen in the body, it may increase the risk of hormone-related cancers such as endometrial, prostate and breast cancer.

The view that all oestrogens are ‘bad’ and cause cancer is a simplistic one. Estradiol (E2) and estrone (E1) are metabolised into at least 14 different species. These breakdown products and have their own specific biological actions; some have the stimulatory properties of estradiol whilst others are weak and antagonistic to other oestrogen molecules. An imbalance of the stimulatory versus weak oestrogen metabolites has been observed to be associated with many different health disorders. Whilst high levels of the 16α-hydroxyestrone stimulatory oestrogen raise cancer risk, lower levels are associated with osteoporosis. In contrast, if the weak oestrogens are high they protect against cancer but inhibit bone growth. Therefore the oestrogen metabolites are not inactive excretion products but powerful molecules in their own right and should be monitored.

Estradiol (E2) is the major oestrogen and is recognised for producing the majority of the functions of oestrogen in the body. It is critical for the development of female reproductive organs, for producing female secondary sexual characteristics and during the menstrual cycle and, with progesterone, prepares the endometrium for implantation.  It helps vaginal lubrication, reduces urinary tract infections and increases sexual desire.  It is also important for brain health, enhancing memory and mood. E2 is interconvertible with E1; E2 to E1 conversion being favoured.

Estrone (E1) is produced from the aromatisation of androstenedione and the reduction of E2 to E1.  It has considerable oestrogenic activity although it is less potent than E2.

Estriol (E3) is a metabolite of E1 and E2. It is a weaker oestrogen which is capable of exerting either antagonistic or agonistic effects depending on dosage, or whether it is given alone or in conjunction with a stronger oestrogen such as E2. It has been shown to be clinically effective for the treatment of menopause-related symptoms such as hot flashes, insomnia and poor memory. In addition, postmenopausal conditions of vaginal atrophy with accompanying dryness, vaginal infections and dyspareunia; and urinary tract changes resulting in recurrent UTIs, urgency, incontinence and frequent urination are helped considerably with E3.

Estradiol (E2) is about 10 times as potent as E1 and about 80 times as potent as E3 in its estrogenic effect. Except during the early follicular phase of the menstrual cycle, its serum levels are somewhat higher than that of E1 during the reproductive years of females. Thus it is the predominant oestrogen during reproductive years both in terms of serum levels and iatrogenic activity. During menopause, E1 is the predominant circulating oestrogen and during pregnancy, E3 is the predominant circulating oestrogen in terms of serum levels.

Low endogenous oestrogen levels are associated with the following conditions:

  • Menopause – immediately before and following the firm cessation of menstruation at menopause, women experience a rapid loss of bone (demineralisation).  It may then plateau after the initial five years and decrease at a rate of 1% annually
  • Hypothalamic amenorrhea – this can occur for a few reasons (excess dieting, anorexia, rigorous exercise, fat loss), one of a large contributor is low levels of oestrogen.  This may also be seen after cessation of the OCP
  • Premature menopause – this occurs rarely in women who experience menopause before the age of 40.  A decline in the production of oestrogen within the ovaries may account to premature bone loss.
  • Premature ovarian failure
  • Hypothyroidism – low thyroid function may be associated with low bone density if left untreated.

The final piece to the puzzle is the reduction in oestrogen levels leading into menopause. The ovaries reduce their production of oestrogen which triggers the elevation of FSH and LH which triggers the characteristic symptoms of menopause. The ovaries and adrenal glands continue to produce some oestrogen, however, if the drop is dramatic and the adrenals cannot cope then the symptoms of menopause can be dramatic until the body balances itself.

The second source of oestrogen is derived from the conversion of androgens to oestrone by the aromatase enzyme.  This process is called ‘aromatisation’ and occurs predominantly in the muscles and fatty tissue (adipose).  Women in the post-menopause phase will derive most of their oestrogen through this aromatisation of androgens.  Often this conversion of oestrogen is enough to sustain them, however, if the adrenals are in poor condition due to a lifetime of stress, nutritional deficiencies etc then the ability of this conversion to occur is decreased and the symptoms of menopause are more extreme.