The heart-disease epidemic vanishes upon closer inspection. It’s based on the proposition that coronary heart disease was uncommon until it emerged in the 1920s and grew to become the nation’s number-one killer. The epidemic was a “drastic development—paralleled only by the arrival of bubonic plague in fourteenth-century Europe, syphilis from the New World at the end of the fifteenth century and pulmonary tuberculosis at the beginning of the nineteenth century,” the Harvard nutritionist Jean Mayer noted in 1975. When deaths from coronary heart disease appeared to decline after peaking in the late 1960s, authorities said it was due, at least in part, to the preventive benefits of eating less fat and lowering cholesterol.

The disease itself is a condition in which the arteries that supply blood and oxygen to the heart—known as coronary arteries because they descend on the heart like a crown—are no longer able to do so. If they’re blocked entirely, the result is a heart attack. Partial blocks will starve the heart of oxygen, a condition known as ischemia. In atherosclerosis, the coronary arteries are lined by plaques or lesions, known as atheromas, the root of which comes from a Greek word meaning “porridge”—what they vaguely look like. A heart attack is caused most often by a blood clot—a thrombosis—typically where the arteries are already narrowed by atherosclerosis.

The belief that coronary heart disease was rare before the 1920s is based on the accounts of physicians like William Osler, who wrote in 1910 that he spent a decade at Montreal General Hospital without seeing a single case. In his 1971 memoirs, Paul Dudley White remarked that, of the first hundred papers he published, only two were on coronary heart disease. “If it had been common I would certainly have been aware of it, and would have published more than two papers on the subject.” But even White originally considered the disease “part and parcel of the process of growing old,” which is what he wrote in his 1929 textbook Heart Disease, while noting that “it also cripples and kills often in the prime of life and sometimes even in youth.” So the salient question is whether the increasing awareness of the disease beginning in the 1920s coincided with the budding of an epidemic or simply better technology for diagnosis.