Estrogen is the primary hormone responsible for female sexual characteristics. The body produces several types of estrogen molecules, some of which have stronger actions than others. These can be interconverted from one to the other as different needs within the body require. Among the many actions estrogen carries out in the body are these below.
Estrogen is important in maintaining tissue elasticity and strength. This aspect of estrogen activity shows up throughout the body. Declining estrogen is partially responsible for the increasing delicacy of your skin as you age as well as the tendency to develop wrinkles. Two areas where estrogen loss to tissues and muscles is of particular concern are the vagina and urinary tract.
Vaginal atrophy makes sex difficult or impossible, due to lack of lubrication and stretch—key elements of arousal and response, not just comfort. Tissues may tear and bleed. Damage as well as the loss of normal cleansing by vaginal secretions opens the way for infections and those infections are much more difficult to treat. Labial irritation from washing with even mild soaps and extreme itching are other aggravations of estrogen-starved genital tissues, and affect about 30% of women who do not supplement postmenopausal hormone levels.
Urinary tract tissues react similarly to estrogen deprivation. Infections are more common and harder to treat. Incontinence, often thought to be an inevitable part of aging, is in fact often due to loss of urinary tract muscle tone in response to low estrogen levels. The urinary tract is so susceptible to estrogen starvation that even the muscles that support the bladder can weaken when levels are too low too long.
Even your gum tissues are affected: estrogen replacement has been shown (also) to lower gum inflammation and loss of teeth due to destruction of the fibers that hold them in place.
Voice changes are a rarely-acknowledged aspect of menopause but can be quite a problem for women who are professional vocalists as well as anyone who relies on their voice a lot. Throat dryness and hoarseness as well as loss of parts of their tonal range are things women may experience.
Estrogen is very important for cardiac and vascular health. Lack of estrogen is believed to be why statistics for male mortality due to cardiovascular disease are so much higher than those of premenopausal women, even though researchers are having a difficult time pinning down the exact mechanisms. In postmenopausal women, cardiovascular disease becomes the leading cause (30-50%) of death. Surgical menopause increases the risk of heart attack seven-fold. Although the risk of clots and strokes may rise in the first year of use (there are mixed research results on this due to lack of distinction between different hrts and hrt delivery routes), adequate estrogen levels have been shown to decrease both heart attacks and strokes by 25-50% and deaths due to them by 50%. Some of the reasons for this include estrogen's effects of lowering blood pressure and relaxing the walls of arteries, improving cardiac output, and decreasing fibrinogen (one of the proteins that creates blood clots) levels. Estrogen also may lower your cholesterol level and improve the balance of blood lipids (this may depend upon the type of HRT you use, however). Estrogen also lowers c-reactive protein, which may correlate to lower risk of cardiovascular disease, although this effect varies with different hrt routes of administration.
Estrogen has many other effects on the brain than vascular. Research has yet to identify the exact mechanism, but women who supplement estrogen after natural menopause seem to show lowered incidence or later onset of Alzheimer's disease (source) and dementia (source). New research also indicates that the severity of Parkinson's disease may be affected by estrogen levels, although there's not universal agreement on that yet.
Estrogen shares some brain receptors with serotonin, another hormone that affects mood. This may be why depression is a common result of low estrogen: if estrogen is not available to fill some of those receptors, serotonin supplies may not be adequate to maintain moods. This interrelationship is at least partially supported by the effectiveness of selective serotonin reuptake inhibitor, or SSRI, antidepressants in treating other menopausal complaints such as hot flashes.
Estrogen seems to be somehow linked to memory itself, especially verbal memory. Women with low estrogen frequently complain of feeling "foggy," losing track of their thoughts, words, objects, or blocks of knowledge such as how to get from one location to another. Nouns are particular victims of this process, leading to those helpless conversational fumblings that are one of the hallmarks of menopausal women. That this is a transmission problem is suggested by the at least partial recovery of this "lost" information and capability once estrogen levels are restored.
Estrogen affects the nervous system through boosting quantities of neurotransmitters such as norepinephrine and glutamate. These neurotransmitters affect mood stability and irritability as well as overall energy levels. While excesses become of interest when we are talking about balancing an excess of estrogen, deficiency can be related to a sluggishness often written off to "getting old and slowing down" or maybe just "you're depressed about your hyst and need to get over it."
One of the most widely-recognized effects of estrogen is in the prevention of the bone wastage known as osteoporosis. Without estrogen, calcium is lost from the bones and not replaced, leading to weakened bones that break easily and heal poorly. After menopause, bones lose roughly 3% of their mass per year for the first five years and then about 1-2% a year. 250,000-300,000 women are hospitalized annually for osteoporosis-related broken bones, and 20% of those women die within the next month. This isn't just a matter of dowager's hump or broken hips: bone loss from the jaws is a major cause of tooth loss in postmenopausal women. Maintaining adequate estrogen levels is shown to prevent or diminish calcium loss from bones and the resulting osteoporosis, although it's not the sole factor required for healthy bone maintenance. There are many online risk evaluation tools that you can find doing a search for "osteoporosis risk calculator" that you might find useful in evaluating your own personal risk level.
Vision is another system that is impaired by lowered estrogen levels. Eye shape changes as hormone levels do, which can affect your need for correction and the fit of your contact lenses. Dry eyes are a frequent effect of low estrogen. This is such a widespread problem that contact lens manufacturers are developing new lens materials to conserve moisture in response to the growing postmenopausal market. Macular degeneration, in which the center of the visual field deteriorates, cannot be treated and is the most common visual disaster in the elderly; glaucoma may also see some preventative action by estrogen, also due to improvements in retinal blood flow (free signup required to read). Maintaining adequate estrogen levels causes a 60% reduction of its occurrence. Cataracts at the front of the lens are less of a risk when estrogen is maintained; back of the lens cataracts do not seem to be affected.
Although it may seem trivial in comparison to other systems affected by hormone levels, the connection between estrogen levels and hair growth and texture has nonetheless the potential to cause considerable anguish. Estrogen has a known effect on the life span of any single given hair, such that drops in estrogen can shorten the life of the hair and cause it to fall out. When you have a whole head of hair reacting to the catastrophic loss of hormones at the onset of surgical menopause, the results can be near-baldness or at least very worrisome extent of hair loss. Typically, the hair regrows in a few months (barring subsequent hormonal instability) and the situation is resolved. Additionally, low estrogen opens the door to a relative testosterone expression that brings with it conversion to a form of testosterone that causes male pattern baldness. High estrogen, on the other hand, decreases levels of certain nutrients (B vitamins and magnesium, especially) that are necessary to manufacture hair. Low thyroid hormone, which is related to high estrogen levels, can also cause hair to become brittle and thin.
Since the ovarian hormones are the sex hormones, there is an obvious connection between sex and estrogen. Part of the sense of wellbeing attributable to effective estrogen levels is feeling and looking "feminine." When estrogen is low, the body may be producing enough testosterone to tilt the balance towards the masculine, causing facial/chest hair growth and head baldness, deepening or coarsening voice, and loss of breast tissue. While estrogen does not of itself directly mediate the libido, it does keep vaginal tissues healthy enough to respond to sexual arousal and it just plain makes you feel sexier. An excess of estrogen, however, can prevent the achievement of orgasm or lessen its intensity.
Lowered levels of estrogen are also linked to impairment of the immune system. The body's defensive cells are less active and infection-killing measures are less toxic to invading bacteria and viruses. Altogether, a woman with lowered estrogen levels is more susceptible to infection and less able to fight off infection once she's ill. Another effect of low estrogen may be worsening of autoimmune disorders, including previously unsuspected ones becoming more obvious.
Estrogen interacts with a number of other hormones in ways that can also have wide-spread effects. For example, it binds thyroid hormone, so that levels of estrogen can influence bioavailable levels of thyroid hormone, and hence one's whole metabolism. In fact, all menopausal women should be tested for thyroid adequacy, since alterations in ovarian hormones can push you over the edge into needing to supplement thyroid (note that it's the alteration in underlying hormone levels, not the taking of HRT per se that does this). Estrogen also plays an important role in insulin-sensitivity. Insulin is the hormone that moves glucose into cells, so that cells are nourished with energy to carry out their functions. Without enough estrogen, glucose metabolism is impeded.
Cancer is one of the big fears that deters women from using estrogen. Unless you carry the breast cancer risk gene or have had breast cancer in the past, however, your risks of developing cancer are much much lower than that of dying from one of the conditions that results from lowered estrogen. In fact, simple lifestyle choices are riskier: your chance of developing breast cancer are higher if you are obese or drink too much alcohol than if you take HRT. Additionally, estrogen seems more to accelerate development (and discovery) of breast cancer than actually cause it, and when it occurs, it is generally of a more treatable, less aggressive variety. On the other hand, increased breast density caused by estrogen means that mammograms are more necessary and must be more carefully read to detect cancers in women with good estrogen levels. You can calculate your personal risks of breast cancer with this tool from the National Cancer Institute.
One sure cancer that estrogen's stimulation of the endometrium (lining of the uterus) is proven to cause is endometrial cancer. Fortunately, by mimicking the natural combination of estrogen plus progesterone, that cancer-causing tendency is squelched when using combined HRT. While women who have had a hyst may think themselves thus immune to this risk, having no endometrium any longer, that may not in fact be the case. Endometriosis sufferers (endometriosis is a disease in which bits of the endometrium escape from the uterus and seed themselves throughout the abdominal cavity) may continue to need progesterone to keep remaining bits of scattered endometrial tissue from turning cancerous. Women in surgical menopause who still have a uterus also carry a special vulnerability to endometrial cancer if they do not protect their uterus from excessive exposure to estrogen as well.
Melanoma, an especially malignant form of skin cancer, is also known to be affected by estrogen. While HRT has been shown in some small studies to slightly increase the risk of melanoma, that risk remains well below the risks due to osteoporosis and cardiovascular disease posed by the consequences of low estrogen levels. As with breast cancer, however, this is a cancer in which lifestyle and familial tendencies must be taken into account in risk assessment. At this point, we don't have enough information (and we're not sure it's out there) to accurately judge this risk. The risk of melanoma itself, outside of the familial, is clearly related to sun exposure but is also related to lowered immune function.
On the good news side of the cancer/estrogen equation, however, colon cancer risks are considered to be lowered by estrogen. Since this is the fourth most common cancer and the second most deadly, this is some counterbalance for other risks.
Before leaving the question of cancer, we want to point out some developments in medical as well as public perceptions of hormones that have occurred in the recent past. There was considerable uproar following news coverage in Dec. 2000 of the inclusion of estrogen on the National Institutes of Health list of cancer-causing agents. This was based primarily on the well-documented association between estrogen and endometrial cancer, with breast cancer cited as a lesser association. Since the endometrial cancer risk is so well dealt with by the addition of progesterone (or similar agents called progestins), this is not considered a reason to avoid its use.
And then in the summer of 2002, cancellation of the Woman's Health Initiative study, which studied Prempro in a large number of considerably-post-menopausal women, due to levels of breast cancer above the study's allowable, led to widespread panic that estrogen was "too dangerous." Subsequent discussion and followup testing has indicated that the culprit in the study results is more likely to have been the particular synthetic progestin, Provera, that was used in the study rather than estrogen itself, and that the study population selection may not have been the best to obtain results that can be generalized to younger populations of women. In fact, the arm of the study that involved women who had had hysterectomies and therefore were taking Premarin alone, without the Provera, actually had a lower-than-normal breast cancer incidence.
So, yeah, estrogen does a lot. It is so important for physical (non-fertility-based) function that even men produce some estrogen and have tissue receptors for it. Even though HRT licensing is restricted to suppression of hot flashes, estrogen really does a great deal more than that, and much of it is pretty non-optional stuff.
