Cardiologists have long known that obesity increases the risk of death from heart failure, but a new study shows that being even slightly overweight--as little as four pounds over--also increases the risk substantially.
That increased risk, furthermore, arises from being overweight itself rather than from fat's effect on hypertension and diabetes. A 15-year study on nearly 6,000 people shows that being overweight alone is responsible for 11% of cases of heart failure in men and 14% of cases in women, a team from the Boston University School of Medicine reports in today's New England Journal of Medicine.
"Most of the time, we think of extreme obesity as a cause of heart failure," said Dr. Robert H. Eckel of the University of Colorado Health Sciences Center, a spokesman for the American Heart Assn. "But these people were not extremely obese.... This is another good reason to lose weight. And even if you can't lose weight, don't gain any more because that would put you in a higher risk group."
The new findings are alarming because obesity has reached "epidemic levels" in the United States and is still increasing, said Dr. Claude Lenfant, director of the National Heart, Lung and Blood Institute, which sponsored the study.
An estimated 61% of adults in this country are considered overweight, according to the study. In particular, 13% of young children and 14% of adolescents are now overweight.
"The results of this study are a wake-up call to a public health problem that we may be addressing 10 to 50 years from now when these obese youngsters become old enough to be at risk of heart failure," said Dr. Daniel Levy of Boston University.
An estimated 2 million to 3 million Americans suffer from heart failure, which occurs when the heart is unable to pump sufficient blood to meet the body's needs. Symptoms include shortness of breath, fatigue and edema (water retention) in the ankles and feet. High blood pressure and diabetes are major risk factors for heart failure. In such cases, the walls of the left ventricle--the heart's main pumping chamber--get thicker and the heart gets flabby and weak, making it difficult to climb stairs, or even to tie one's shoes.
The death rate from heart failure, moreover, has remained constant over the last four decades, even while the death rate from heart disease has dropped by 60%, Lenfant noted.
The new results were obtained from the participants of the Framingham Heart Study, a landmark epidemiological study that began in 1948.
Dr. Ramachandran S. Vasan of Boston University and his colleagues followed 5,881 men and women for 15 years, monitoring their weight and the development of heart failure. One-third of the women and half the men were overweight. About 16% of both sexes were considered obese.
"The debate has been whether it is obesity or other factors associated with it that is causing the risk," said Dr. Greg Fonarow of the UCLA School of Medicine. "What this study is trying to get at is whether obesity in and of itself is a true risk and a true contributor to the development of heart failure. According to them, it is."
A limitation of the study was that virtually all of the participants were Caucasian. Obesity is a major problem among other ethnic groups, but this study was not able to address those issues.
The team grouped the subjects by their body mass index or BMI, which is the person's weight in kilograms divided by the square of their height in meters. A BMI calculator is available at www.nhlbisupport.com/bmi/bmicalc.htm. People are considered normal if their BMI is less than 25, overweight if it is from 25 to 29.9 and obese if it is 30 and above.
The team concluded that, independent of all other factors, each 1-point increase in BMI caused a 5% increase in risk for men and a 7% increase for women. For an individual who is 5 feet 10 inches tall, a 1-point increase is equal to 6 pounds.
Overall, they concluded, the risk of heart failure was 34% higher in those who were overweight and doubled in those who were obese.
"Even after we accounted for the effects of all the other risk factors, there was an independent effect of adiposity [being overweight] on heart failure," Vasan said.
Heart failure is "a grim prognosis, a bad condition to have," he said. "This should be an impetus for people who do not have an optimal BMI to move in that direction."
The team is not sure how obesity increases the risk, Vasan added. Some laboratory studies have shown that obese rats, for instance, have deposits of fatty particles in heart muscle cells that lead to cell death, a phenomenon called lipotoxicity. Or, he added, the extra weight may simply make the heart work too hard.
Eckel cautioned that other factors are even more important in raising the risk of heart failure, including age, a previous heart attack, valve disease and high blood pressure. This combination of factors can raise the risk much higher in the obese.