For decades, heart disease has had the dubious honor of being the leading killer of Americans. Most heart-related deaths happen among the elderly, by far the largest at-risk group for cardiovascular disease. But a new study finds that an alarming portion of heart failure cases are occurring in a much younger group - under age 50 - and overwhelmingly among African Americans.
In the first large-scale study to document the extent of the race gap in heart disease, researchers report that one in 100 black adults develop heart failure in their 30s and 40s - a rate 20 times higher than that of similarly aged white men and women. In fact, the heart failure rate among young black adults was more like that of white men and women in their 50s and 60s. "What these data point out is that it's important to recognize that disease patterns differ in different populations," says Dr. Kirsten Bibbins-Domingo, one of the study's authors and co-director of the Center for Vulnerable Populations at the University of California, San Francisco, and San Francisco General Hospital. "We would have completely missed this at-risk group had we only been looking at older age groups. We would have also missed them if we had not been studying African Americans in large numbers." (See the top 10 medical breakthroughs of the past year.)
The new report, published in the March 19 issue of the New England Journal of Medicine, is a large government-funded survey that began in 1985. The aim of the study was to document the frequency of heart disease among young adults, so researchers recruited more than 5,000 volunteers from four cities and tracked them for 20 years, measuring their blood pressure, weight, cholesterol, fasting blood sugar and kidney function. These tests were repeated six times over the two-decade period.
The black adults who developed heart disease early had at least one of four risk factors - high blood pressure, being overweight, chronic kidney disease or low levels of "good" cholesterol (high-density cholesterol, or HDL). Blood pressure and heart risk rose in step: for each 10 mm increase in diastolic blood pressure (the bottom number of the ratio), the risk of having heart failure in their 40s doubled. For each 5.7 increase in body mass index (BMI), a ratio of weight and height, the risk of developing heart failure increased by 40%. And each 13.3 mg/dL drop in HDL levels also boosted the risk of heart disease by 40%.
But the largest risk factor for heart failure among this group was chronic kidney disease, a condition that is often triggered by untreated diabetes and obesity. Black adults with chronic kidney disease experienced a stunning 20-fold jump in their risk of heart failure, compared with black adults without kidney disease. "Here we have tangible evidence that heart failure in the young is a real dilemma," says Dr. Clyde Yancy, president-elect of the American Heart Association.
Although young black adults in the study were more likely than whites to have risk factors for heart disease - on average, the baseline blood pressure of blacks who went on to develop heart disease was 10 mm higher than that of whites - Bibbins-Domingo and her co-investigators also showed that this population did not get appropriate medical treatment for their conditions, if any at all. At the beginning of the study, 75% of black participants with hypertension were not taking medication for their condition; 10 years later, 57% still remained untreated. (The study did not provide a corresponding figure for white hypertension patients, but past research has documented a well-known disparity in treatment.)
"The number of individuals with controlled blood pressure is embarrassingly low," says Yancy. "That indicates a problem not only of understanding the biology of blood pressure, and why it occurs more frequently in young African Americans, but also why we aren't intervening more aggressively and effectively to treat it. Does it represent some form of bias? Of stereotyping? Or lack of access to care?"
It is probably a combination of all of those factors that prevents adequate treatment of hypertension in the black community, and the end result is that African Americans are more likely to develop further risk factors for heart disease, none of which are being treated aggressively enough to protect this population from early illness. "Our ability to intervene early and appropriately is limited," says Yancy. "That is something that we need to change because I think it's a crisis." Studies like this one that document the problem could be an important first step in sounding the alarm.