MONDAY, Nov. 1, 2004 (HealthDayNews) -- Apparently healthy obese people are suffering silent heart damage that sets the stage for serious cardiac problems, a new Australian study finds.
Using advanced ultrasound technology, the researchers found the blood-pumping left ventricle of severely obese persons had a significantly weakened ability to contract and expand.
And smaller but still significant weaknesses in blood-pumping ability were found in people with lesser degrees of obesity or overweight, the study said.
"We detected subtle changes that we think are steps along the way to developing heart failure," said study author Thomas H. Marwick, a professor of medicine at the University of Queensland.
The research appears in the Nov. 2 issue of Circulation.
Heart failure is a progressive and potentially fatal loss of the heart's ability to pump blood. Some 550,000 new cases of congestive heart failure are diagnosed in the United States each year. It is the primary cause of approximately 50,000 deaths annually and a contributing cause in more than 200,000 other deaths.
One key finding in the new study was these first signs of future heart failure were detected in obese persons who had no existing heart disease and were free of high blood pressure and diabetes, two major risk factors for heart failure. They also had a normal ejection fraction, the conventional measure of blood-pumping ability.
The study included 33 individuals of normal weight, with a body mass index (BMI) less than 25. (Body mass index is a ratio of weight to height and is used to determine if a person is healthy weight, overweight or obese.) There were also 26 overweight participants, with a BMI between 25 and 29.9; 37 participants with mild obesity, a BMI between 30 and 34.9; and 46 severely obese people, with a BMI of 35 or higher.
The study showed "a direct relationship" between the degree of obesity and the loss of pumping ability, Marwick said.
He and his colleagues have started trials to see if the heart-weakening effect can be reversed. The working hypothesis is that obesity does its damage by limiting the body's ability to respond properly to insulin, the hormone that allows the body to convert blood sugar to energy for cells. "We suspect other causes, but insulin resistance is a likely and plausible mechanism," Marwick said.
One trial is designed to determine whether exercise training can reduce insulin resistance. "We think it should be effective; no data yet," Marwick said.
Several other mechanisms may also be at work in obese individuals, said Dr. Ann Bolger, associate professor of medicine at the University of California, San Francisco, and a spokeswoman for the American Heart Association.
"We know that the larger the body is, the harder the heart has to work, so it builds itself up," she said. "This comes at a cost. The properties of the heart wall have to change for the worse, and what you have basically is an overworked heart."
Extra fat tissue also causes increased production of hormones that can lead to scarring of heart muscle, Bolger said.
"Finally, obesity can cause sleep apnea, which has a tremendous effect on the heart," she said.
The Australian results should be taken as a warning by people who are overweight but regard themselves as otherwise fit, Bolger said.
"Someone says, 'I feel fine.' When I've had heart tests, the heart seems normal,' " she said. "What this study says is that you can't bank on that. Even if you are young and healthy, obesity causes changes in heart muscle that get worse with time."
The American Heart Association has more on why obesity is bad for the heart.