Estradiol is the estrogen our ovaries produce the most of during our reproductive years, so when you take estradiol in HRT, you are, to some degree, replacing the estrogen you used to make with its identical twin.

The most commonly prescribed estradiol is Estrace; however, you also can get generic estradiol or a newer brand of estradiol, Gynodiol. In all cases, it is a natural bio-identical estrogen, made from plant sources that are micronized -- broken down into little pieces -- so it is easily absorbed and used by your body.

When you take estradiol orally, it enters your gastrointestinal tract, is metabolized by your liver, and is converted into estrone -- the estrogen your body has the most of after menopause.

According to studies, micronized estrogen helps prevent bone loss and so fights against osteoporosis, helps lower cholesterol, and appears to prevent the risk of cardiovascular disease. Another plus: Estradiol is the form of estrogen that appears to be involved with memory, learning, and other mental functions that often decline with age.

While most studies have been conducted using a standard dose of 1 mg. of Estrace (which is comparable to the .625 of Premarin), recent studies have also shown that a half dosage -- .5 mg -- also helps fight osteoporosis if taken with a calcium supplement. One other often unreported plus: micronized estradiol increases sex hormone-binding globulin, so women who with high levels of androgens that cause such side effects as excessive facial hair growth, may see improvement with this estrogen.

But there has been some concern about taking micronized estradiol: Estradiol is the strongest form of estrogen and the one that is most carcinogenic. According to a Scandinavian study of over 23,000 women, there was an increased risk of breast cancer over time -- up to 1.7 times risk after nine years. However, the study looked at women taking 2 mgs of estradiol, which is double the most commonly prescribed dose of 1 mg. Moreover the study has been criticized because only 1 in every 30 women were sent questionnaires. Yet again, then, this is a case where it’s difficult to say whether the findings of a study should concern you.

On the whole, most doctors believe that micronized estradiol is a good choice of estrogen for women wanting to prevent osteoporosis and heart disease and to minimize menopausal symptoms. And, since it is naturally occurring and identical to the estrogen the ovaries produce, it’s a good choice for women who prefer a natural estrogen to a conjugated one.

• Standard dosage: 1 mg. Also available in 2 mgs, which may be prescribed if the initial 1 mg dose fails to help eliminate symptoms; and .5 mg, which if combined with calcium, has been shown to prevent osteoporosis.  Most recently, Gynodiol became available in a 1.5 mg dosage -- since many women need something in between the 2 and 1 mg levels.
• Pros: Plant-derived; identical to the estrogen your body makes; easily absorbed; helps fight osteoporosis, heart disease and eliminates symptoms
• Cons: Higher than usual doses were shown to increase the risk of breast cancer in one study (however, the findings of this study have been criticized); easily excreted from your system, so if you take it in the morning, you may have symptoms in the nighttime. You can easily get around this, though, by taking a half dose in the morning and another half dose before bedtime.