Hidden in Plain Sight

How We Overlooked One of the Leading Drivers of Heart Disease

A new study published in JAMA found that lead exposure contributes to 3.5 million deaths each year, including nearly 30% of coronary heart disease mortality worldwide. Our 2018 study, which began more than a decade ago, was part of a broader effort to understand lead as a cardiovascular risk factor. The findings are striking—and raise a deeper question: how did we overlook something so large for so long?

In 1912, one of the most respected and influential physicians in the world made an observation that now reads like a warning. William Osler, writing in The Principles and Practice of Medicine, noted that chronic lead exposure played “an important role in the causation of arteriosclerosis.” It was a passing remark, tucked into a larger discussion. Easy to miss. Easy to forget.

And forget it we did.

Within a few decades, coronary heart disease would become the leading cause of death in the United States. Over the next century, we would search relentlessly for its causes—studying cholesterol, blood pressure, smoking, diet, and genes—while largely ignoring the possibility Osler had quietly flagged.

That omission matters more than we might like to admit.

A Puzzle Hidden in Plain Sight

Every medical student learns the modern story of heart disease. It is, we are told, a disease of lifestyle and metabolism—too much cholesterol, too much salt, too many cigarettes, too little exercise, perhaps the wrong genes.

There is truth in that story. Antihypertensive drugs reduce strokes and heart attacks. Statins lower cardiovascular risk. Smoking cessation saves lives. Clinical strategies work, and they are essential.

But the story is incomplete.

Coronary heart disease did not drift gradually into human experience. It surged. In the early decades of the 20th century, as industrialization accelerated, heart disease rose sharply. By mid-century, it had become the dominant cause of death.

Then, just as mysteriously, something changed.

In the 1970s and 1980s, heart attacks began to decline—rapidly and unexpectedly, at a scale that surprised even seasoned observers. Physicians took notice. In 1978, more than 80 scientists gathered at what became known as the Decline Conference to understand why nearly 190,000 fewer deaths had occurred than expected.

They had no shortage of explanations—changes in diet, early shifts in smoking, improvements in care. As Robert Levy, the director of the National Heart Institute, later wrote, “We have too many, rather than too few, possible explanations.”

And yet one category barely entered the conversation: environmental exposures.

The Story We Preferred

For most of the 20th century, we framed coronary heart disease as a disease of personal behavior. That framing—promoted by the Framingham Study—had a certain elegance. It was intuitive, actionable, and fit neatly into the clinical encounter. Physicians could measure cholesterol, prescribe medication, and counsel patients about smoking or diet.

It also had a subtle advantage. It located both the problem and the solution within the individual—and, in doing so, let industry and government largely off the hook.

What it did not do was explain why entire populations became sick at the same time. Why did heart disease rise so dramatically in the early 20th century? Why did it decline so sharply in the late 20th century? Why did it follow patterns that seemed to mirror industrialization more than individual choice?

To answer those questions, we need a different lens.

A Different Way of Seeing

The British epidemiologist Geoffrey Rose offered one. In A Strategy of Preventive Medicine, he drew a distinction between clinical strategies and population strategies. Clinical strategies focus on individuals—diagnosing and treating disease once it appears. Population strategies look upstream—identifying and removing the conditions that cause disease before it develops.

For hypertension, the contrast is clear. A clinical strategy prescribes medication. A population strategy asks why blood pressure is rising across millions of people at once. The clinical strategy treats one patient at a time. The population strategy tries to eliminate the need for treatment altogether.

Rose’s insight helps explain something we often overlook: when diseases become widespread, their causes are usually embedded in the environment, not just in individual behavior.

As I explored in an earlier essay, populations living outside industrialized environments rarely experience the steady rise in blood pressure and heart disease that we take for granted. When those same populations adopt modern conditions, the diseases appear—often within a generation.

That pattern is hard to explain without an environmental cause.

The Lead We Didn’t See

While heart disease was rising through the early 20th century, another trend was unfolding in parallel. Lead exposure was increasing.

Beginning in the 1920s, tetraethyl lead was added to gasoline. The additive improved engine performance and quickly became ubiquitous. As cars multiplied, so did lead—dispersed into the air, soil, and dust of cities and towns across the country.

By the 1960s, the average American had blood lead levels exceeding 130 parts per billion. That is an extraordinary level of exposure—1000 times that of preindustrial humans.

And yet, lead remained largely absent from the dominant narrative of heart disease.

Part of the reason was regulatory. Industry argued that lead should not be restricted without clear evidence of harm at the population level. That presumption—that chemicals are safe until proven otherwise—shaped both policy and scientific inquiry for decades.

When a risk factor is presumed safe, it is less likely to be studied, less likely to be measured, and less likely to be included in models of disease. It becomes, in effect, invisible.

A Natural Experiment

What followed was one of the most revealing natural experiments in public health. As lead was removed from gasoline, blood lead levels in Americans fell dramatically—from over 130 parts per billion in 1976 to about 30 in 1990, and eventually below 10 ppb today.

At the same time, something else happened. Hypertension declined.

In the mid-1970s, roughly one in three American adults had high blood pressure. By the early 1990s, that number had dropped to one in five. These were not trivial changes. They were exactly the kind Geoffrey Rose had anticipated: small shifts in the average producing large changes in the distribution.

Coronary heart disease followed a similar trajectory. As exposure declined, mortality fell. No single factor explains a complex disease, but the alignment was striking.

We had conducted a massive, unplanned experiment—and failed to recognize what it was showing us.

A Reframing

The latest Global Burden of Disease reported that lead exposure contributes to 3.5 million deaths annually, including nearly 30% of coronary heart disease mortality worldwide.

This is not a minor revision. It is a reframing.

Lead is no longer a peripheral concern. It is a central contributor to one of the leading causes of death. And it does not act solely through blood pressure. It acts directly on the artery—promoting oxidative stress, impairing endothelial function, and accelerating atherosclerosis.

In retrospect, Osler’s observation seems less like a curiosity and more like a missed opportunity.

Why We Missed It

How do you overlook a leading cause of death for more than a century?

Part of the answer lies in how we think about disease. We focus on what we can measure easily in individuals—cholesterol, blood pressure, behaviors. These are visible, actionable, and clinically useful.

Environmental exposures are different. They are diffuse, shared, and often operate at low levels across entire populations. Their effects are subtle in individuals but substantial in aggregate.

They are harder to see—and easier to ignore.

But the explanation goes further.

The media, including outlets like the New York Times, rarely highlighted the possibility that environmental exposures like lead were driving heart disease. The dominant narrative remained focused on diet, smoking, and medical care.

Industry played a role as well. Companies that produced lead had strong incentives to minimize its risks and emphasize uncertainty.

And our medical system—built around pharmaceuticals, procedures, and devices—naturally focused on treatment. It is far easier, and often more profitable, to treat disease than to prevent it by changing the environment.

Together, these forces shaped what we studied, what we measured, and ultimately, what we believed.

What We Get Wrong—and What We Need to Do

When we view heart disease solely as a problem of lifestyle and metabolism, prevention remains downstream. We treat high blood pressure, lower cholesterol, and intervene after disease has already developed.

These interventions are indispensable. They save lives every day.

But they cannot fully offset upstream exposure.

The epidemic itself was shaped by environmental conditions. Its prevention will require addressing those conditions.

That means broadening our approach. We need clinical strategies that treat individuals—and population strategies that reduce risk across entire communities.

We have seen what population strategies can achieve. Removing lead from gasoline reduced exposure for millions and was followed by declines in hypertension and heart disease. Clean air regulations improved life expectancy. Smoke-free laws reduced heart attacks within months.

These interventions did not depend on individual behavior change. They altered the environment. They made it harder to become sick, not easier.

The lesson is straightforward: if exposures are causing disease across entire populations, then reducing those exposures will prevent disease on a scale that treatment alone cannot match.

A Final Question

The story of lead and coronary heart disease is not just about one metal. It is about how we understand disease.

Again and again, we have failed to identify upstream causes because we have failed to look for them. We have overattributed disease to genetics and lifestyle while underestimating the role of environmental exposure.

This imbalance is not harmless. It delays prevention, allows harmful exposures to persist, and narrows the scope of what we consider possible.

The rise of coronary heart disease in the 20th century was not solely a story of personal habits. It was also a story of industrialization.

The decline in heart disease was not only the result of better treatment. It was also the result of reducing exposure.

We are still living inside that story. The question is whether we are willing to see it clearly. Because until we do, we will continue to treat disease—patient by patient—while overlooking the conditions that make disease inevitable.

And the most important opportunities for prevention will remain, as they have for more than a century, hidden in plain sight.