Actions of Progesterone by Joseph J Collins, RN, ND

In women, progesterone is a steroid hormone produced primarily by the ovaries and adrenal glands. Progesterone has a direct affect on the function of the reproductive system, the nervous system, the cardiovascular system and the skeletal system. Blood sugar levels, skin and other tissues and functions are also significantly influenced by progesterone. Like all steroid hormones, excessive amounts of progesterone can contribute to a number of increased health risks. Though proper progesterone levels are critical for the prevention of endometrial hyperplasia and endometrial cancer, the actions of this hormone extend far beyond endometrial health. Therefore it is crucial that proper levels also be maintained in women who have had a hysterectomy.
Following is a list of some of the actions and functions of progesterone. More information and more references can be found in the book Discover Your Menopause Type?

The Menstrual Cycle and the Endometrium
Progesterone prevents development of endometrial cancer 1. Low progesterone with unopposed estrogen may be one cause of dysfunctional uterine bleeding 2. Progesterone may help decrease uterine contractions, cramping and pain 3, 4.

The Vagina & Urinary Tract
Excessive progesterone may increase urinary incontinence and even counteract the beneficial effects of estrogen in maintaining urinary control 5, 6, 7, 8.

The Libido
Excessive progesterone may decrease libido due to antiestrogen and anti-androgen effect 9, 10. As well as decreasing libido, excessive levels may induce depression 11.

Blood Sugar & Insulin
While estrogens help the cells of the body utilize glucose more efficiently by making them more sensitive to insulin, progesterone can cause a decrease in insulin sensitivity, having an effect on blood sugar that is similar glucocorticosteroids 12. This interference with the action of insulin can interfere with normal glucose uptake and cause insulin resistance 13, 14, 15, 16, 17.
The ability of progesterone to interfere with proper function of insulin and glucose has since been associated with gestational diabetes 18, 19, 20 as well as hormone replacement therapies 21,15, 22, 12 and has been been observed in both synthetic & non-synthetic progesterone 20, 23, 24, 12. Even the high progesterone levels which occur naturally during the luteal phase can induce insulin resistance in some women 21, 16.

The Brain – Mood & Memory
Progesterone and its metabolites result in increased relaxation and reduced anxiety in a way that is similar to the effects of benzodiazepines 25, 26 by a direct effect on neurotransmitter receptors called Gamma-AminoButyric Acid type A (GABAA) receptors 27. When progesterone levels drop a woman can experience withdrawals similar to the withdrawal seen with benzodiazepine, barbiturate, and alcohol withdrawal 29.
Excessive levels may cause decreased coordination, slowed reflexes, depression and impaired memory and reasoning skills 30, 31, 32, 33, 34. The sedating effects of excessive progesterone can cause drowsiness and even induce sleep 35, 32, 36. The nerve calming effect of progesterone is so pronounced that both natural progesterone and medroxyprogesterone have both been shown to decrease seizures in women with epilepsy 37, 38.
Progesterone has a protective, stimulating effect on breathing patterns during sleep, resulting in decreased incidence of sleep apnea, a serious condition in which the body is deprived of oxygen 39, 40, 41, 42.
The action of progesterone on GABAA receptors have been associated with an increase appetite and food intake 43, 44, 45.

The Breasts
Progesterone insufficiency may play a role in the development of breast cancer 46, however progesterone may also play a role in the proliferation of some progesterone receptor forms of breast cancer 47. This increased risk is associated with the increased production of IGF-1 by breast cells stimulated by excessive progesterone 48, 49 - resulting in the proliferation of several forms of breast cancer cells 50.

The Skin
Though progesterone does not increase skin thickness 51, it does increase blood flow to the skin 52 resulting in an increased ability to sweat and loose the extra heat through the skin 53. Progesterone can also raise body temperature, enhancing the ability to tolerate cold 53.

Bones & Osteoporosis
Progesterone has stimulating effect on the bone building osteoblasts resulting in increased bone building activity 54, 55, 56, 57, 58, 59, 60. This is due to a direct stimulation of the progesterone receptors in osteoblast bone cells 61, 62, as well as an increased secretion of IGF-1 and other growth factors by the bone cells exposed to porgesterone 63, 64, 65. The most positive effect is seen when estrogen & progesterone are used in combination 66.

The Heart
Natural micronized progesterone may cause a significant lowering of in blood pressure in postmenopausal women with mildly to moderately high blood pressure 67, possibly due to the vasodilating effect of action of progesterone 68.
Natural micronized progesterone will not reduce the good HDL levels that are enhanced by estrogen replacement 69, and will result in higher HDL than when synthetic progestogens are used 70.
This lipoprotein (a) benefit of estrogen is not diminished by either synthetic (medroxyprogesterone acetate) or natural micronized progesterone 71, 72.

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