Is Hormone Replacement Therapy Safe for the Heart? The Timing Hypothesis and Cardiovascular Risk in 2026

Even as the science evolved, many women had a hard time getting that study out of their heads. Today, much of the fear surrounding MHT and cardiovascular health is based on interpretations that are more than 20 years old. Modern research tells a very different story, especially when we take timing and formulation into account.

The current medical consensus is clear. When started early, modern MHT is not only safe for the heart for most women, it can actually protect it.

Does MHT increase heart disease risk?

For most healthy women under age 60 or within 10 years of menopause, MHT reduces heart disease risk by around 30%-50%. This is known as the “Timing Hypothesis.” Early initiation supports blood vessel health and improves cardiovascular biomarkers, while starting MHT decades later requires a different risk assessment.

The Timing Hypothesis and the 10-Year Window

The Timing Hypothesis explains why when you start MHT matters as much as whether you start at all.

Estrogen plays a key role in cardiovascular health. It helps maintain flexible blood vessels, reduces inflammation, and supports healthier cholesterol patterns. During perimenopause and menopause, declining estrogen levels remove this protection, which is why women’s heart disease risk rises sharply after menopause.

In Alloy’s interview on menopause and heart health, cardiologist Dr. Jayne Morgan explains it this way:

“Estrogen has cardioprotective factors to it. It also has anti-inflammatory properties. Chronic inflammation is a causative factor for the progression of hardening of the arteries, which can lead to heart attacks.”

When estrogen therapy is started while the endothelium, the inner lining of the blood vessels, is still relatively healthy, it helps preserve vascular function. Large analyses now show that women who begin MHT within 10 years of their final menstrual period or before age 60 experience significantly lower rates of coronary heart disease and overall mortality compared to women who never use hormone therapy.

That’s the population that was largely misrepresented in early interpretations of the WHI data.

When the Risk Profile Changes After 60 or 70

Starting MHT later in life is not the same clinical situation.

For women who are more than 20 years past menopause, some degree of arterial plaque may already be present. Estrogen doesn’t cause plaque, but its effects on older, more rigid arteries can differ from its effects on healthy vessels.

That’s why contemporary guidelines emphasize individualized screenings rather than blanket rules. There is no strict age cutoff, but women starting MHT after 70 generally require more careful cardiovascular evaluation.

Modern MHT Looks Very Different Than Legacy Therapy

Much of the lingering fear around blood clots and stroke comes from older oral estrogen pills. Oral estrogen passes through the liver first, which increases clotting factors and explains the elevated clot risk seen in earlier studies.

Modern transdermal estrogen, which can be delivered through patches, gels, creams, or sprays, bypasses the liver entirely. Current evidence shows that transdermal estrogen doesn’t increase the risk of blood clots or stroke compared to baseline.

Progesterone choice also matters. Older synthetic progestins were associated with negative cardiovascular effects, including increased blood pressure. Micronized, body-identical progesterone has a neutral effect on blood pressure and does not counteract estrogen’s vascular benefits, which makes it the preferred option for women concerned about heart health.

The Lipoprotein(a) Connection and 2025 Research

One of the most important developments in understanding MHT and heart disease risk involves Lipoprotein(a), often called Lp(a). Lp(a) is a genetically determined cholesterol particle that increases the risk of heart attack and stroke in women. It is not routinely tested and does not respond well to lifestyle changes.

New research published in 2025, including work by Nudy et al. and data presented at The Menopause Society’s annual meeting shows that estrogen-based hormone therapy can lower Lp(a) levels when started during perimenopause or early postmenopause. 

This finding helps explain why estrogen cardioprotection is strongest when therapy is initiated early and reinforces the importance of biomarker-based cardiovascular assessment.

It is also important to note that the reduction in Lp(a) is greater for oral estrogen than transdermal estrogen due to oral estrogen’s impact in the liver.  This highlights the importance of an individual risk-based assessment and discussion with your provider to determine your ideal MHT regimen.

It is also important to note that the reduction in Lp(a) is greater for oral estrogen than transdermal estrogen due to oral estrogen’s impact in the liver. This highlights the importance of an individual risk-based assessment and discussion with your provider to determine your ideal MHT regimen.

Frequently Asked Questions About MHT and Heart Health

• Does MHT cause heart attacks?

Absolutely not! In fact, modern research shows the opposite for most healthy women. When MHT is started within 10 years of menopause, it’s associated with a 30%-50% reduction in heart disease risk.

• Is there an age limit for starting MHT?

There is no hard cutoff, but benefits are greatest when MHT is started before age 60. Women starting MHT after 70 should undergo individualized cardiovascular screening due to the possibility of existing arterial plaque.

• Does MHT cause blood clots?

Older oral estrogen pills carry a small increased clot risk. Transdermal estrogen does not, because it is absorbed through the skin and bypasses the liver.

• How does MHT affect blood pressure?

Unlike older synthetic progestins, micronized progesterone has a neutral effect on blood pressure, making it a safer option for cardiovascular health.

The Bottom Line

Much of what women have been told about MHT and heart disease risk is rooted in outdated interpretations of older studies. Current 2025 clinical standards paint a far more reassuring picture.

A secondary analysis published in JAMA Internal Medicine confirms that hormone therapy does not increase cardiovascular disease risk in women ages 50 to 59. For many, it reduces it.

As Dr. Morgan emphasizes in her Alloy interview, understanding estrogen’s role in heart health is critical as women age:

“Prior to menopause, women have half the risk of heart disease compared to men. Once we lose estrogen, that protection changes.”

Don’t let decades-old myths dictate your cardiovascular future. If you’re in perimenopause or early postmenopause, talk with one of the menopause-expert physicians at Alloy about whether you’re still within the optimal window for cardioprotection.