“Estrogen deficiency” is a common phrase. It is often used to describe people who are one year or more beyond their last period. However, estrogen deficiency has been diagnosed in 13- or 14-years-olds who have just experienced their first period. Or in a thin or stressed university student whose menstruation suddenly stopped. It could also be found in a teenager who is eventually diagnosed as having polycystic ovary syndrome (PCOS) after persistent adolescent acne, unwanted facial hair and irregular periods. Finally, someone with estrogen deficiency might be having irregular or skipped periods as a perimenopausal 35-plus-year-old.

Odd, isn’t it, that so many people lack estrogen?

Estrogen deficiency can be a serious condition in cisgendered women. It is linked to serious diseases like osteoporosis and heart attacks. A teenager whose period has stopped has low estrogen levels; she is losing bone density and risks later life fractures. Women living with PCOS are also at increased risk for diabetes, heart attacks, and endometrial and ovarian cancers as well as infertility. The typical perimenopausal woman develops high  cholesterol and may be at increased risk for heart attacks. Menopause itself is linked to an increased risk of osteoporosis and heart attacks, as well as vaginal dryness and decreased interest in sex.

The big problem with estrogen deficiency as a symptom or diagnosis is that it is a catchall term that plays into a cultural notion that estrogen is what makes a woman a woman. I am now 77 years old and am 20 years into my own menopause. Yet, I robustly argue that I am not “estrogen deficient.” Why? Because my low estrogen and progesterone levels are normal for my age. And menopause is a normal life phase.

Does “estrogen deficiency” even exist?

Not alone, it doesn’t. Why? Because low progesterone levels (what could be called “progesterone deficiency”) always occur first. Our brain has a protective, fine-tuned response to many stressors, so ovulatory disturbances that have lower or absent progesterone levels, and that happen without our knowing it within regular cycles, occur long before estrogen levels become low. Plus, to make progesterone at all, the body must first have estrogen. Estrogen’s mid-menstrual cycle peak must occur before ovaries can release an egg and then make high progesterone levels. So, singling out estrogen doesn’t make sense.

Together estrogen and progesterone are a crucial part of the human female reproductive system. Estradiol (a type of estrogen) and progesterone work in a coordinated pattern during the menstrual cycle and collaborate in producing healthy basic cellular function. Estrogen is an important growth stimulator. But cell growth, also called proliferation, can cause genetic mistakes and lead to cancer. Therefore, progesterone’s “job” is to decrease estrogen’s proliferation effects as well as to increase cell maturation and specialization.

In describing a teenager without a period, or with cycle intervals that are unusually long (more than 5 weeks), the only way that “estrogen deficiency” makes any sense, is to believe that estrogen is the only menstrual cycle hormone. Important new information says that, to be healthy as well as fertile, women need balanced actions of both estrogen and progesterone during menstruating years. That means women usually have regular, normally month-apart, ovulatory (with at least 10 days of high progesterone) menstrual cycles. Without these balanced levels of estrogen and progesterone levels for most of our menstruating years, we are at risk for osteoporosis, heart attacks and breast and endometrial cancers when older.

Thus, the term, “estrogen deficiency,” does not accurately and scientifically describe amenorrhea, oligomenorrhea, PCOS, perimenopause nor menopause. Further, it doesn’t tell us what therapy is best for each of these potential issues across a woman’s life cycle. The goal of these therapies in younger women should be to restore a healthy estrogen-progesterone balance with regular, ovulatory cycles.

So, why are do we keep hearing about “estrogen deficiency”? Because it is a very effective marketing term. It was made by and for estrogen-selling companies. It implies that estrogen, and estrogen alone, is a necessary and effective treatment. Note that it arose during the same era as the equally inaccurate term “hormone replacement therapy” or “HRT.”

In summary, whenever a younger woman skips a period (unless she is pregnant!), she is missing both estrogen and progesterone. A woman with PCOS without flow for months, paradoxically has normal or high estrogen and testosterone levels, but likely low progesterone. When a perimenopausal woman starts getting night sweats and premenstrual symptoms, she already has higher-than-usual-menstrual cycle estrogen levels, and lower progesterone levels. And when a menopausal woman has been without periods for a year, her progesterone levels are reliably low, but she may still have intermittently normal (or even high) estrogen levels.

We know that because one or two of every 10 women over 40 years of age, who has not menstruated for a year, will have another, natural period. A woman can tell it is a normal but “rogue flow” and not cancer if she had breast tenderness, bloating or felt PMS-like symptoms before it started.

I now understand “estrogen deficiency”. It is a myth obscuring the importance of balanced estrogen and progesterone.