What Is the SWAN Study? Menopause Research Explained

If you've read anything on this site about how long hot flashes last, when bone loss speeds up, or why perimenopause symptoms feel so unpredictable — you've already met SWAN, even if you didn't know its name. Almost everything modern medicine understands about the menopause transition traces back to one study. Here's what it actually is, and what it found.

What SWAN actually is

SWAN — the Study of Women's Health Across the Nation — is a long-running, NIH-funded research project that has followed more than 3,300 women through hormone change since 1996. It's not a supplement study, an industry survey, or a small clinical trial. It's a genuine population study: women recruited across seven U.S. research sites, deliberately including white, Black, Hispanic, Chinese, and Japanese American women, so the findings would actually reflect how different women experience this transition — not just the women who happen to show up in a doctor's office asking for help. Nearly three decades and 17 rounds of data collection later, it remains the largest, longest, most detailed look at hormone change that exists.

We're spending a whole page on one study for a reason: a lot of what circulates as "common knowledge" about menopause — including guidance many doctors were trained on — predates SWAN, or hasn't caught up to it. When we correct outdated information elsewhere on this site, this is usually where the correction comes from.

Why this study is different from most menopause research

Before SWAN, most of what was known about menopause came from women who sought treatment for symptoms — which meant the research skewed toward women with the most severe experiences. SWAN instead started with a broad, community-based population, so it could describe what's actually typical, not just what's typically reported in a clinic. It also followed the same women for decades, which is what let researchers untangle a question that's genuinely hard to answer any other way: how much of what changes at midlife is caused by the hormonal transition itself, versus just getting older. Those two things happen at the same time in every woman's life, which makes them almost impossible to separate — unless, like SWAN, you're tracking the same women's hormones and health for 25-plus years.

What SWAN found: hot flashes last longer than you've been told

For years, the standard guidance — the kind you'll still find in a lot of places — was that hot flashes and night sweats typically last 6 months to 2 years. SWAN's data tells a different story: the median total duration was 7.4 years, and for women whose symptoms started back in perimenopause rather than after their final period, the median stretched to nearly 12 years. Duration also varied by race and ethnicity, with Black women in the study experiencing the longest median duration.

This isn't a small correction. If you're making decisions about treatment based on "it'll probably be over in a year or two," SWAN's data suggests planning for something longer is often more realistic.

What SWAN found: your hormones don't decline in a straight line

SWAN's data is the actual source behind the staging framework — STRAW+10 — that shows up throughout our Learn library. It's also where the "estrogen doesn't just smoothly decline" explanation comes from: SWAN tracked real hormone levels in real women over time and found a genuinely variable, sometimes erratic pattern, not a steady downward slope. That's part of why symptoms can feel so inconsistent month to month during perimenopause — the data backs up what a lot of women already suspected from experience.

What SWAN found: bone loss starts before your last period

One of SWAN's more clinically important findings: the fastest phase of bone loss doesn't wait for menopause to officially arrive. It's concentrated in a roughly three-year window spanning the final menstrual period — starting about a year before it and continuing for a couple of years after — before the rate of loss slows down. In other words, your skeleton is already responding to hormone change while your periods are still happening, just less predictably.

What SWAN found: late perimenopause is a real window of vulnerability for depression

SWAN found that women were significantly more likely to experience new-onset depression during late perimenopause specifically — including women with no prior history of depression. This held up even in follow-up research using structured clinical interviews, not just symptom questionnaires. It's a meaningful finding: it suggests late perimenopause isn't just "a rough patch" in a vague sense — it's a specific, identifiable window where mood risk goes up, and it deserves to be taken seriously rather than dismissed as something to just push through.

What SWAN found: the "brain fog" dip is real, temporary, and not fully explained by other symptoms

SWAN measured actual cognitive performance — not just self-reported brain fog — and found a measurable dip in processing speed and verbal memory during late perimenopause. Two things are worth knowing about this finding. First, it resolved in postmenopause — this wasn't a permanent decline. Second, when researchers checked whether sleep problems, mood symptoms, or hot flashes could fully explain the dip, they couldn't — something about the transition itself seems to affect cognitive performance beyond just its downstream effects on sleep and mood. That's genuinely useful to know if you've been told your brain fog is "just" poor sleep or "just" stress.

What SWAN found: menopause and aging affect your heart differently

Because SWAN followed the same women for decades, researchers could tell apart which cardiovascular changes tracked with the hormonal transition itself and which tracked with simply getting older. Their findings suggest certain cardiovascular changes are more closely tied to the menopause transition specifically, while others — like rising blood pressure and BMI more broadly — track more closely with chronological aging. That distinction matters for how doctors think about prevention and timing of care around this transition, rather than treating every midlife health change as automatically "a menopause thing" or automatically "just aging."

Why this matters for you, not just for researchers

We're not walking through SWAN's findings to be academic about it. It matters because so much of the outdated information still circulating — the "6 months to 2 years" hot flash timeline, the idea that brain fog "isn't real," vague reassurance that bone health only becomes relevant "after" menopause — traces back to a time before this data existed. When you read something on this site that corrects one of those ideas, SWAN is very often where that correction comes from. Good information changes what you expect, what you ask your doctor, and how seriously you take what you're feeling. That's the whole reason a 25-year research study belongs on a wellness brand's website.

Frequently asked questions

What is the SWAN study? The Study of Women's Health Across the Nation — a long-running, NIH-funded research project following more than 3,300 women through the menopause transition since 1996, across seven U.S. sites and multiple racial and ethnic groups.

Why is the SWAN study considered so important? It's the largest and longest population-based study of the menopause transition, and its long follow-up period let researchers distinguish effects of the hormonal transition itself from the effects of aging — something shorter or clinic-based studies can't do as reliably.

What did SWAN find about how long hot flashes last? A median total duration of 7.4 years — significantly longer than the older "6 months to 2 years" guidance still commonly cited, and closer to 12 years for women whose symptoms began in perimenopause.

Does SWAN research apply to all women? SWAN deliberately included white, Black, Hispanic, Chinese, and Japanese American women and found real differences in symptom duration and timing between groups — which is itself an important finding, since a lot of earlier menopause research wasn't as representative.

Is SWAN still ongoing? SWAN has followed its original cohort for nearly three decades, into later adulthood, and continues to produce new research on long-term health outcomes related to the menopause transition.

References

American Journal of Managed Care / PMC — The Study of Women's Health Across the Nation: From Midlife Onwardhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC6840943

El Khoudary SR, et al. — The Menopause Transition and Women's Health at Midlife: A Progress Report from SWAN. Menopause, PMC https://pmc.ncbi.nlm.nih.gov/articles/PMC6784846

Avis NE, et al. — Duration of Menopausal Vasomotor Symptoms Over the Menopause Transition. JAMA Internal Medicine https://pubmed.ncbi.nlm.nih.gov/25686030

PMC — Bone Health During the Menopause Transition and Beyondhttps://pmc.ncbi.nlm.nih.gov/articles/PMC6226267

Al-Safi ZA, Santoro N — SWAN: Key Findings to Date and More to Comehttps://journals.sagepub.com/doi/10.2217/WHE.13.15

Weber MT, et al. — Menopause-Associated Symptoms and Cognitive Performance: Results From SWAN, PMChttps://pmc.ncbi.nlm.nih.gov/articles/PMC2915492

Related Her Reclaim guides

• What Is Perimenopause?
• What Is Menopause?
• 34 Common Symptoms of Perimenopause and Menopause
• Brain Fog and Hormone Change
• Mood, Anxiety, Irritability, and Hormonal Transition
• Sleep, Night Sweats, and Fatigue During Menopause

Twenty-five years of data exist so you don't have to guess. That's the whole point of research like this — and the whole reason we build every guide on this site the same way: check it against the real evidence, then tell you the truth about what it says.