In the long history of understanding, diagnosing, and treating heart disease, the Framingham study of 1948 remains a benchmark. Before the study, despite decades of research and observation, doctors didn’t know what caused heart disease or why people were dying from heart attacks.
What was known was that “diseases of the heart” had become the leading cause of death among Americans, killing more than 460,000 in 1948 alone. To frame it another way, 418,000 Americans (mostly soldiers) died during World War II in or as a result of combat. In the three years after the war, heart disease had killed more than three times as many Americans—and the rate of death was increasing at an alarming clip.
A group of medical researchers proposed a definitive longitudinal (over time) study of people to determine once and for all the factors behind the epidemic of heart disease. The researchers chose the town of Framingham, Massachusetts, because it was close to their research centers based in Boston. The town was chosen not because it was special but instead because its population profile seemed to match that of most of the country: it had a foundation of longtime residents, a fairly recent infusion of new immigrants, and an emerging middle class.
In 1948, Framingham had a population of about 28,000. Remarkably, 5,209 residents volunteered for the original heart study, which, by the way, continues today with 15,000 volunteers from a population of 63,000, including many who are first- and second-generation offspring of the original volunteers.
When the study began, what seem today to be such obvious risk factors for coronary artery heart disease—for example, the correlation between cigarette smoking and high blood pressure—were still unknown. Incredibly, some medical professionals believed an elevated blood pressure might even be good for you. The eminent U.S. cardiologist Paul Dudley White in 1937 suggested that “hypertension may be an important compensatory mechanism which should not be tampered with, even if we were certain that we could control it.” By the 1950s many doctors still thought that unless it was severe, hypertension was a relatively benign condition.
Equally incredible was the popular notion that filtered, versus nonfiltered, cigarettes lowered the risk of heart disease. (That wasn’t definitively disproven by the Framingham study until the 1970s.)
But of all the results of the famed Framingham study, none were more important than its findings about cholesterol and specifically that high levels of low-density lipoprotein (LDL) cholesterol may be a major cause of clogged and narrowed arteries (arteriosclerosis). Before Framingham, it was generally thought these conditions were normal parts of aging, occurring universally as people became older, and there was nothing much to be concerned about. After Framingham, researchers could clearly see from the data that the volunteers who had high LDL cholesterol levels also had the highest incidence of heart disease and suffered the most from its severest forms, including heart attack and cardiac arrest. It’s because of the Framingham volunteers and the research team who studied them that we now know that people with high cholesterol have about twice the risk of heart disease as people with lower (normal) levels of cholesterol and LDL.
Cholesterol is a waxy, fat-like substance. Your body needs some cholesterol. It’s essential for making the cell membrane and cell structures and is vital for synthesis of hormones, vitamin D, and other substances, but it can build up on the walls of your arteries and lead to arterial heart disease and stroke when you have too much in your blood.
Low-density lipoprotein cholesterol is known as bad cholesterol (because it clogs the arteries). High-density lipoprotein (HDL) cholesterol is known as good cholesterol (because it’s essential for cell membrane synthesis), and high HDL levels in the blood are associated with fewer heart attacks and strokes.
High blood cholesterol is a condition that causes the levels of certain bad fats, or lipids, to be too high in the blood. This condition is usually caused by lifestyle factors, notably diet, but as we learned in the last chapter, heart disease can be inherited, and so can a proclivity for higher than normal LDL cholesterol levels. Genetic studies have found that related family members tend to have similar levels of LDL and HDL cholesterol. Less commonly, high cholesterol is caused by other medical conditions or some medicines.
The Framingham findings were so important because the problem of excessive cholesterol, which leads to clogged arteries, is pervasive: nearly one in every three Americans has LDL cholesterol levels that are unhealthy. That is, more than 102 million American adults (age twenty or older) have total cholesterol levels at or above 200 mg/dL, which is above healthy levels. More than 35 million of these people have levels of 240 mg/dL or higher, which puts them at higher risk for heart disease. Combine this with high levels of triglycerides, the most common type of body fat, and, well, then you have the recipe for heart attack, stroke, and silent heart disease.
Use the chart in table 7.1 to determine with your doctor whether your cholesterol levels are safe.
Table 7.1.
| Desirable Cholesterol Levels | |
|---|---|
| Total cholesterol | Less than 200 mg/dL |
| LDL (“bad” cholesterol) | Less than 100 mg/dL |
| HDL(“good” cholesterol) | 60 mg/dL or higher |
| Triglycerides | Less than 150 mg/dL |
Here’s the kicker to the whole problem of cholesterol: Like silent heart disease itself, high blood cholesterol does not cause specific symptoms. However, your doctor can do a simple blood test to check your levels. The National Cholesterol Education Program recommends that adults get their cholesterol checked every five years.
Within the cells, cholesterol is the precursor molecule in several biochemical pathways. For example, in the liver, cholesterol is converted into bile, which is then stored in the gallbladder. Bile is made up of bile salts, which help in making the fats more soluble and easier to absorb. Several animal fats are sources of cholesterol. Animal fats are complex mixtures of triglycerides and contain lower amounts of cholesterols and phospholipids.
Major dietary sources of cholesterol include cheese, egg yolks, beef, pork, poultry, and shrimp. Cholesterol is not found in plant-based foods; however, plant products such as flax seeds and peanuts may contain cholesterol-like compounds called phytosterols, which are beneficial and actually help in lowering cholesterol levels.
Saturated fats and trans fats in food are the worst culprits in raising blood cholesterol. Saturated fats are present in full-fat dairy products, animal fats, several types of oil, and chocolate. Trans fats are present in hydrogenated oils. These do not occur in significant amounts in nature and are found mainly in fast foods, snack foods, and fried or baked goods.
We’ll take an even deeper dive into the differences between saturated and unsaturated fats in Chapter 10.
Now, before we close, we’ll tackle one more myth about high-cholesterol levels: it’s only a problem for adults. While it’s true that the vast majority of those who suffer from high LDL cholesterol are adults with a skew toward middle-aged and older adults, increasingly we’re finding the problem is affecting youth.
Two recent studies published in the Journal of the American Medical Association found that heart disease risk factors—including elevated LDL cholesterol levels—increasingly were showing up in children. Additional research compiled in the Bogalusa Heart Study found that childhood cholesterol measurements predicted future artery thickness.
The Bogalusa Heart Study is like the Framingham Heart Study in that both have tested a population over several decades, but it is different in several important ways. First, the town of Bogalusa in southern Louisiana is racially mixed between whites and blacks, while Framingham was almost entirely white. Second, the study purposefully includes children. Finally, the population studied is largely rural (versus Framingham’s suburban population), and it is the only controlled, longitudinal study of its kind located in the South.
Headed by Tulane University medical professor Gerald Berenson, MD, the team of researchers began collecting data in 1972, making it the longest-running biracial health study in the world. The study has generated thousands of peer-reviewed articles. “We started our study with school-age children, from 5 to 17 years old. Because of the results we went down to preschool age, 2.5 to 5.5 years old,” said Berenson in an interview in Global Health Magazine. Ultimately, the Bogalusa team sought birth records to try to answer questions about birth weight and risk of heart disease and diabetes. A majority of the people who began participating in the study as schoolchildren continued to come back to the Bogalusa clinic for follow-up health checks as first years and then decades rolled by, creating a generation of heart health data.
Key findings of the study include the following:
•The major etiologies of adult heart disease, atherosclerosis, coronary heart disease, and essential hypertension begin in childhood. Documented anatomic changes occur by five to eight years of age.
•Cardiovascular risk factors can be identified in early life.
•The levels of risk factors in childhood are different from those in the adult years. Levels change with growth phases, notably in the first year of life, during puberty and adolescence, in the transition to young adulthood, and in adulthood.
•Autopsy studies clearly indicate atherosclerosis and hypertension begin in early life.
The take-home message from Bogalusa? Adult heart disease is now beginning in childhood for many individuals, and elevated LDL cholesterol levels are a primary culprit in this new phenomenon. Dietary control of cholesterol, LDL and HDL, should be addressed at all ages.