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What is Estrogen?

Women produce two key sex hormones, estrogen and progesterone. Estrogen has many physiological functions in the body and plays a critical role in reproduction and women’s physical development. Women also produce testosterone, but in very low amounts. Together, estrogen and testosterone play a very important role in the growth and maintenance of a woman’s reproductive tissue as well as bone mass.

Estrogen’s Role in the Female Body

Estrogen produces the physical changes that occur at puberty. These include:

  • The start of the menstrual cycle.
  • Growth of breasts.
  • Growth of underarm and pubic hair.
  • Shaping the female pelvis.

As a woman grows, estrogen performs other functions:

  • Promoting bone growth and preventing bone loss.
  • Maintaining normal levels of cholesterol.
  • Regulating mood.
  • Softening skin.
  • Increasing libido.

The key source of estrogen in women is the ovaries. In addition, small amounts of estrogen are produced by the adrenal gland. From these two locations, estrogen circulates in the blood and goes to other parts of the body, including the brain.

Estrogen & the Menstrual Cycle

Estrogen levels fluctuate during the menstrual cycle. The highest levels occur during ovulation or the middle of your menstrual cycle, and the lowest levels are found at the end of the menstrual cycle. The levels peak at about 14 days into the cycle, at which point, the eggs are released from the ovaries. This is the concept behind birth control pills. Combination birth control pills contain both progesterone and estrogen and prevent ovulation by maintaining a more consistent level of these hormones. Because estrogen levels do not peak, ovulation does not occur.

As women age, the production of estrogen drops, and they enter a physiological state that is known as menopause. There is a stage of perimenopause where estrogen levels fluctuate and then eventually the production of estrogen falls to very low levels, thus starting the stage of menopause.

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