Before I open a diseased coronary artery during bypass surgery, I often run a gloved finger gently along its surface as it lies on the beating heart. What I feel tells me a great deal. Instead of a soft, flexible vessel, the artery feels irregular, with hard nodules beneath my fingertips, almost like tiny beads embedded in the vessel wall. Those bumps are calcium deposits, signs of a long process that has stiffened and narrowed what should be a living, responsive artery.

The author performing a heart surgery.

Bill Frist, MD

Then I take the scalpel and make a careful incision into the artery.

Inside, the contrast is stark. A healthy artery is smooth and supple, its inner lining delicate, almost translucent. Here, the surface is roughened and distorted. Pale yellow plaques protrude into the channel where blood should flow freely. Some are soft and waxy. Others are hardened and calcified, fixed in the wall almost like stone. What should be a wide-open passage carrying life-sustaining blood to the heart muscle has been reduced to a narrow channel, barely able to sustain flow.

As I looked down into that opened artery, something unexpected happened. My mind jumped from the vessel before me to a much larger living world beyond it. The pathology in the surgical field no longer felt confined to the operative field. It seemed connected to a broader pathology in nature itself, the loss of balance in the natural world, intensified by human activity and carried back into the body as disease. I found myself asking a new question: how much of what I was seeing inside that artery was being shaped by the broader world beyond it?

The purpose of the operation is clear: restore full blood flow to the heart muscle. In coronary artery bypass surgery, we create a new pathway for blood to reach the heart. We sew a segment of vein from the leg, or sometimes an artery from the chest, into place to reroute blood around the blockage. The graft quite literally jumps over the diseased portion of the artery.

It is a remarkable operation. Blood flow is restored. The heart muscle is protected.

But the disease itself remains.

We bypass the obstruction. We do not remove the underlying disease that created it.

Unless those deeper causes are addressed, the pathology progresses. And only by addressing them can we hope to prevent what we have become so skilled at bypassing.

That was the beginning of the journey. And it led to the first question.

What caused this artery to become diseased in the first place?

For most of my professional life, medicine answered that question in familiar terms: age, blood pressure, cholesterol, diabetes, genetics.

Those matter. They still do.

But over time, I began to see that the story was much larger. The heart does not fail in isolation. It is influenced, day after day and year after year, by the natural world and the human-shaped world around it.

Once I began to see that, the lens widened again. And the next question followed naturally.

If the cause does not lie in the heart alone, where does it lie?

The answer, I came to believe, lies predominantly in the world out beyond the heart: in the natural world, in the human-shaped world, and in the ways we live within both.

In the air we breathe.

In the food we eat.

In the water we depend on.

In the soil beneath our feet.

In the heat we endure.

In the stress we carry.

In the systems we build and inhabit.

Over the same decades that I was operating on hearts every day, the world out beyond the heart was changing. The climate was warming. Heat waves were intensifying. Wildfires were becoming more frequent. Oceans, too, were warming and becoming more acidic. Natural habitats were being degraded or lost. Food systems were shifting toward more processed and less nourishing patterns. The deeper truth was not simply that change was occurring, but that it was accelerating. In the span of my own life and work, the pace of disruption had quickened in ways that made the connection harder and harder to dismiss. These were not isolated developments. They were signs of a broader disruption in the delicate balance of the living world.

At first, these seemed like two separate concerns: concerns about the natural world outside us, and concerns about human health inside us.

But over time, they no longer felt separate to me.

The disruption of harmony in the natural world was not separate from the disorder taking shape in the human body. It was helping drive it. The degradation outside was being carried inward and expressed as biologic disorder inside.

Inflammation rose.

Vascular function shifted.

Hormonal systems changed.

The delicate equilibrium on which health depends began to erode.

What I was seeing in the artery was not merely a local problem. It was the anatomic expression of a broader disruption.

That recognition changed the way I think about human health and mental health. For years, I had focused on repair. And repair matters. Rescue matters. Bypass surgery matters. But bypass surgery only restores blood flow; it does not remove the deeper disease. The pathology progresses unless we address the forces that produced it.

Once the world beyond the heart came into view, I needed to understand the pathway. And that led, naturally, to the next question.

How, exactly, does the world around us reach the heart and the rest of the body?

The answer begins with circulation.

The arteries and veins form the immediate living environment of the heart. They deliver oxygen and nutrients. But they also carry the signals and exposures of the world beyond the body.

Particles inhaled into the lungs.

Chemicals absorbed from food and water.

Microbes entering through the skin.

Signals generated by heat, smoke, stress, and unstable conditions.

All of it enters the bloodstream. The circulation is also the body’s distribution system, carrying these signals and exposures not only to the heart but to the lungs, kidneys, brain, adrenal glands, and every other organ, each affected in its own way.

And once there, it reaches one of the body’s most vulnerable and consequential surfaces: the vascular endothelium.

This thin inner lining of blood vessels helps preserve balance. When healthy, it protects. When injured, disease begins.

Inflammation rises.

Plaque forms.

The vessel stiffens.

By the time the disease is visible to my surgeon’s eye, much of the damage has already been done. Early endothelial dysfunction is now understood to precede more advanced atherosclerosis.

Once that pathway became clearer, the next question became inevitable.

What, then, are the major forces in the living world around us that drive this process?

Air pollution is one of the most visible.

Fine particulate matter inhaled into the lungs triggers inflammation, oxidative stress, endothelial injury, and increased clotting. Over time, it accelerates atherosclerosis. At times, the effects are immediate. Days with worse air quality are followed by increases in heart attacks, arrhythmias, and hospitalizations.

That is no longer speculative. The American Heart Association concluded that particulate exposure is associated with higher risk of myocardial infarction, stroke, arrhythmias, heart failure, and cardiovascular death. A New England Journal of Medicine review described air pollution as a major global cardiovascular risk factor and estimated that pollution was responsible for 9 million deaths worldwide in 2019, with about 61.9 percent of those deaths due to cardiovascular disease.

Smoking belongs here too. It is often described as a behavior, but it is also direct inhaled pollution, carrying toxic particles and chemicals into the bloodstream and accelerating the same disease process.

And then comes climate change.

Simply put, climate change is a cardiovascular stress multiplier.

Heat places direct strain on the heart. Blood thickens. Heart rate rises. Fluid is lost. The system works harder under more difficult conditions.

But warming does more than that. It amplifies the harms already acting on the body.

It magnifies pollution.

Hotter air traps pollutants.

Wildfires increase smoke.

Ozone rises.

On the hottest days, the heart is already under strain at the very moment pollution levels are rising.

The two reinforce one another.

Heat and pollution do not merely coexist. Inside the body, they intensify one another’s harm, amplifying inflammation, endothelial injury, and cardiovascular strain.

Wildfire smoke adds another layer.

Unstable weather adds still more strain.

Unstable weather patterns can also reach the heart through mental and emotional stress. Wildfires, storms, displacement, and interruptions in access to hospitals and care heighten anxiety and uncertainty. Those experiences raise stress hormones, including cortisol, and place still more strain on the cardiovascular system.

What is changing is not simply the presence of these forces, but their frequency, their intensity, and their overlap. Large international studies have linked temperature extremes with higher cardiovascular mortality. A 2023 Circulation study found that extreme heat and fine particulate pollution together were associated with greater myocardial infarction mortality, with the highest risk when both occurred simultaneously. The National Oceanic and Atmospheric Administration has also reported that recent years rank among the warmest on record globally and across the United States. Other studies have linked wildfire smoke exposure to increases in cardiovascular hospitalizations, ischemic heart disease events, and out-of-hospital cardiac arrest.

The natural world also reaches the heart through something even more familiar.

The food we eat.

What we now understand is that what we eat influences inflammation, endothelial function, blood pressure, metabolism, and plaque formation. Over time, it helps determine whether arteries remain open and resilient or gradually become diseased.

But the story of food does not begin on the plate. It begins much earlier—in soil, water, farming practices, and the systems that produce what we consume each day.

Food is both behavior and exposure.

When I testified before Congress on the emerging Food Is Medicine movement, I reflected on a simple realization from my own career: in all my years of medical practice, I wrote thousands of prescriptions, yet I never once wrote a prescription for food.

That is beginning to change.

What we now understand is that food is not simply fuel. It is information. It is exposure. It is a driver of biology.

And because it is shaped upstream—by soil, water, and the systems that produce it—the health of the food system and the health of the population are inseparable. The American Heart Association’s dietary guidance and the randomized PREDIMED trial support the central role of diet quality in cardiovascular outcomes, and newer work increasingly frames food systems as both a human-health issue and a planetary issue.

And once the causes came into focus, one final question remained.

If disruption and degradation in the living world help create disease, can restoring and protecting the natural world help prevent it?

What we now understand is that it can.

One of the most powerful ideas emerging in science and public health is something called nature-based solutions.

That term may sound abstract, but the idea is straightforward. It means using natural systems—forests, wetlands, grasslands, healthy soils, urban trees, rivers, coastlines, and other ecosystems—to address human challenges such as climate change, pollution, extreme heat, flooding, food insecurity, and declining health.

In practical terms, it can mean restoring wetlands, protecting forests, improving soil, designing greener cities, restoring habitats, and preserving biodiversity. These, we now know, can cool neighborhoods, filter pollution, lessen stress, strengthen resilience, and help restore the living systems on which health depends.

These are not aesthetic choices. They are biological interventions. They change the conditions in which the human body must function. And in many cases, they are among the most cost-effective and scalable health interventions available to us.

One vivid example comes from the Green Heart Project in Louisville, Kentucky. Researchers at the University of Louisville, with support from the National Institutes of Health and The Nature Conservancy, set out to test a simple but powerful idea: if we improve the physical world around people, can we also improve what is happening inside their bodies?

To explore that question, they planted more than 8,000 trees and shrubs in selected neighborhoods, including areas near major roadways where residents were exposed to traffic, heat, and other urban stressors. In other words, they used nature itself as an intervention. They then measured biological markers of cardiovascular risk in the people living there.

One of those markers was high-sensitivity C-reactive protein, a well-established indicator of systemic inflammation and cardiovascular risk. Reported findings showed that residents living in the greener neighborhoods had roughly 13 to 20 percent lower levels of this marker than residents in nearby comparison areas. The full peer-reviewed outcomes literature continues to evolve, so these findings should be interpreted with appropriate care. But the direction is clear: improve the natural world around people, and you may begin to improve the biology within them.

That is a profound shift.

It suggests that nature is not simply something we protect for its own sake.

It is also something that helps protect us.

And it points toward an idea that has become clearer to me with each passing year: nature is medicine.

Not in a sentimental sense.

In a biologic sense.

Nature can cool the places where people live.

Nature can filter pollution.

Nature can reduce stress.

Nature can strengthen resilience.

And, as this project suggests, nature can help lower some of the inflammatory burden carried within the human body.

This is one of the reasons I have come to care so deeply about nature, habitat, and climate, and one reason I have chosen to focus much of my work through The Nature Conservancy.

Nature, in this sense, is not scenery.

It is part of the infrastructure of health.

Once we understand that the health of the heart is inextricably tied to the health of the world around it, we are called to a broader responsibility.

If degraded air, damaged ecosystems, unhealthy food systems, polluted water, and a destabilized climate are contributing to disease inside the human body, then protecting and improving the world around us is no longer peripheral. It becomes central to protecting human health itself—our individual health, our family’s health, and the health of the communities in which we live.

And the benefits are not distant.

They are immediate.

They are personal.

They are unfolding in the body now.

They are measured in the air we breathe, the heat we endure, the food we eat, the stress we carry, and the biology unfolding inside us every day.

Why I am optimistic

For many people, conversations about climate change, biodiversity loss, and the natural world are framed almost entirely in terms of danger, decline, and sacrifice. That is understandable.

But it is incomplete.

There are real reasons for concern.

There are also real reasons for optimism and hope.

I am optimistic for three reasons.

First, the science and the tools have advanced dramatically.

We have more tools today than at any point in history to reduce pollution, strengthen resilience, protect nature, and improve health at the same time.

And we have the chance to do so in a way that honors the generations of children and grandchildren who will follow us.

The science has advanced dramatically over the past decade. Public understanding and support are improving. In some areas, especially nuclear, the policy and regulatory environment is beginning to move in the right direction. Gallup reported in 2025 that support for nuclear energy in the United States had risen to 61 percent, a near record high. The ADVANCE Act became law in 2024, and the Nuclear Regulatory Commission has since been pursuing reforms intended to improve licensing efficiency while maintaining safety.

Advances in technology, artificial intelligence, parallel computing, and supercomputing are accelerating discovery and deployment across energy, agriculture, and natural systems.

We can accelerate cleaner forms of energy that reduce the pollution burden carried into our lungs, blood vessels, and hearts. That includes wind and solar, but also nuclear, hydrogen, and, in time, fusion. Each can play a larger role as energy demand rises with economic growth, industrial modernization, artificial intelligence, and large data centers. Cleaner energy is a climate strategy. It is a health strategy too. Fossil fuel pollution does not remain outside us. It is inhaled, absorbed, circulated, and internalized. It damages the endothelium, injures the bloodstream, and places harmful stress on the heart, the lungs, and the brain.

That is a crucial point.

This is not a choice between human progress and the health of the natural world. We do not need to slow growth, innovation, jobs, or prosperity. Indeed, strong economic growth and prosperity are at the heart of the American Dream. But we must guide them with greater wisdom, toward systems that do less harm and create more resilience.

Second: scale. We can now act at scale in ways that were not possible even a decade ago.

We are no longer limited to small, isolated efforts.

New financial mechanisms—such as Project Finance for Permanence, nature bonds, and green bonds—are unlocking billions of dollars for long-term protection and restoration of natural systems. These approaches allow governments, investors, nonprofits, and communities to work together, aligning capital with conservation at a scale that was previously unimaginable.

We can now think, and act, at scale.

Recent initiatives such as Enduring Earth bring this into focus, helping protect vast landscapes and ecosystems across multiple countries through coordinated partnerships and long-term financing. And we now have organizations that operate from local to global. The Nature Conservancy, for example, works in more than 80 countries. Organizations such as the World Wildlife Fund and Conservation International are doing the same. These partnerships matter. They bring together science, capital, policy, and local knowledge in ways that allow real progress.

This is not government alone.

It is shared responsibility, shared resources, and shared action.

Third, and perhaps most importantly, nature has restorative power.

When pressure is reduced, nature recovers.

I saw this firsthand four weeks ago at Palmyra Atoll. When invasive rats were removed and the stressors on the system were lifted, the ecosystem began to rapidly restore itself. Seabirds returned. Native trees flourished. Nutrient cycles reconnected. Coral systems strengthened. Fish populations rebounded. The system began to move back toward balance

The same principle applies more broadly.

When we stop degrading natural systems, they begin to recover.

And there is a parallel in the human body.

When blood flow is restored to the heart, the muscle recovers. When a splinter is removed, inflammation resolves and healing begins. The body is built to restore balance when the forces causing injury are reduced.

Nature is the same.

That is a profoundly hopeful idea.

Damage is real.

But repair is possible.

And prevention is better still.

For me, once that connection became clear, something as vast as planetary health no longer felt distant or abstract. It became immediate and personal.

It is about your heart.

Your health today.

Your family’s health.

Your child’s future.

I have focused here on the heart and the coronary artery because that is where my own life in medicine was spent. But the heart is only one example. The same outside world that affects the coronary arteries also affects the lungs, kidneys, brain, immune system, hormonal system, and every other tissue the circulation touches.

The heart does not experience the natural world as scenery.

It experiences it as biology.

This is why protecting nature, preserving biodiversity, reducing pollution, strengthening resilience, and addressing climate change matter so deeply to human health.

We cannot treat our way out of a disease that we continue to create.

If we want healthier hearts, we must look upstream.

The heart depends on the world around it.

And if we want healthier hearts, healthier families, and healthier communities, we must care for the natural world that sustains them.