The Forgotten Estrogen

The Forgotten Estrogen

Estradiol is often described as the estrogen that matters.

It is the estrogen most commonly measured, most frequently discussed, and most often credited with influencing reproduction, bone health, cognition, cardiovascular function, and mood.

If someone were asked to name the most important estrogen in the human body, estradiol would almost certainly be the answer.

Estrone is rarely part of the conversation.

This seems reasonable.

Estrone binds estrogen receptors less strongly than estradiol and is frequently described as a weaker estrogen. In many discussions, estrone appears less like a hormone with its own biological role and more like a less potent version of something else.

The hierarchy appears obvious.

Estradiol is important.

Estrone is secondary.

Yet one of the most significant hormonal transitions in human life creates a problem for this explanation.

As women enter menopause, estradiol declines dramatically.

Estrone becomes the dominant circulating estrogen.

At nearly the same time, rates of depression, anxiety, sleep disturbances, mood instability, and cognitive complaints increase.

This does not prove estrone causes these changes.

It does, however, raise an interesting question.

If estrone is simply a biologically insignificant version of estradiol, why does the body increasingly rely on it during one of the most physiologically important transitions in human life?

The answer may reveal something about how hormones are organized.

The Estrogen That Replaces Estradiol

The human body produces three primary endogenous estrogens:

• Estradiol (E2)
• Estrone (E1)
• Estriol (E3)

During the reproductive years, estradiol dominates.

After menopause, that relationship changes.

Ovarian estradiol production falls substantially, while estrone becomes the predominant circulating estrogen. Much of this estrone is produced outside the ovaries through aromatization in adipose tissue.

This observation is easy to overlook.

Yet it is biologically strange.

If estrone were merely a weaker version of estradiol, it would seem inefficient for the body to rely so heavily upon it during later life.

Biology rarely maintains metabolically active signaling molecules without reason.

The assumption that estrone is simply a weaker estrogen may therefore be incomplete.

The Brain Does Not Ignore Estrone

For decades, estrogen research focused heavily on reproductive physiology.

More recently, researchers have recognized that estrogens exert profound effects throughout the brain.

Estrogen receptors are distributed throughout the hippocampus, amygdala, hypothalamus, and prefrontal cortex — regions involved in memory, emotional regulation, stress processing, and executive function.

These are not peripheral neurological systems.

They help determine how humans perceive, interpret, and respond to their environment.

Estrone participates in this network.

It crosses into the central nervous system, interacts with estrogen receptors, and contributes to the broader estrogenic environment influencing brain function.

More importantly, evidence suggests estrone and estradiol may not be biologically interchangeable.

Research examining postmenopausal women has reported differences in neural activity associated with estrone and estradiol exposure, particularly within memory-related brain regions. Rather than behaving as stronger and weaker versions of the same signal, these hormones may produce distinct patterns of biological response.

This distinction is important.

A weaker signal is not necessarily the same signal.

Biology frequently reuses similar molecules to generate different outcomes depending on context.

A Clue Hidden in Menopause

The menopausal transition has long been associated with increased vulnerability to mood disorders.

Researchers have consistently observed increased rates of depressive symptoms, anxiety, irritability, sleep disruption, and emotional instability during this period.

The conventional explanation is straightforward.

Estrogen declines.

Mood changes follow.

There is substantial evidence supporting this idea. Estrogen signaling influences serotonin, dopamine, GABA, neuroplasticity, and stress-response pathways. Changes in estrogen exposure can therefore influence emotional regulation.

But the hormonal story may be more complicated than a simple estrogen deficiency model.

Because estrogen does not disappear after menopause.

It changes form.

Estradiol falls.

Estrone becomes dominant.

Several studies have reported associations between estrone levels and measures of mood, depression, sleep quality, and psychological well-being in postmenopausal women. These findings do not establish causation, nor do they prove estrone is harmful.

What they do suggest is that estrone may be participating in biological systems far more actively than its reputation would imply.

The question may not be whether estrone causes depression.

The question may be whether estrone has biological functions that have been overshadowed by decades of focus on estradiol.

Potency and Importance Are Not the Same Thing

Hormones are often ranked according to strength.

The strongest hormone receives the most attention.

The weaker hormone receives less.

But biology is rarely organized around potency alone.

Testosterone is not merely a stronger version of DHEA.

T3 is not merely a stronger version of T4.

Different hormones frequently occupy different positions within larger physiological networks.

Estrone may be no different.

Viewed through this lens, estrone begins to look less like a backup hormone and more like a hormone associated with a different physiological state.

Estradiol dominates during reproduction.

Estrone dominates during aging.

Those are very different biological environments.

Different metabolic conditions.

Different reproductive priorities.

Different stressors.

Different patterns of tissue signaling.

Perhaps the mistake is assuming estrone exists to replicate estradiol.

It may instead exist to support estrogen signaling under conditions where estradiol is no longer the primary signal.

The Forgotten Estrogen

The most common question asked about estrone is whether it is weaker than estradiol.

The answer is yes.

But that may be the least interesting thing about it.

The more interesting observation is that biology shifts toward estrone during one of the most significant endocrine transitions humans experience.

At the same time, changes occur in mood, cognition, sleep, stress responsiveness, and overall neurological function.

Whether estrone contributes directly to these changes remains an active area of investigation.

What is already clear, however, is that estrone is not biologically silent.

It reaches the brain.

It interacts with estrogen receptors.

It becomes the dominant estrogen during later life.

And it appears in scientific studies examining mood and psychological health.

We often rank hormones according to potency.

Biology may rank them according to context.

Estradiol may be the dominant estrogen of reproduction.

Estrone may be the dominant estrogen of a different physiological state entirely.

If so, estrone is not simply a weaker estrogen.

It is an estrogen whose role we may not yet fully understand.

And that possibility may be far more interesting than the label “weak estrogen” ever suggested.

-Evan Moon, DC, MSHGG