May 2, 2011 -- A new study shows that people with coronary artery disease who carry extra fat around their waists appear to have an increased risk of dying compared to people who store their body fat elsewhere.
The study pooled and reanalyzed data on nearly 16,000 people with coronary artery disease from around the world. It found that those who were centrally obese, as measured by waist-to-hip ratio and waist circumference, had up to twice the risk of dying compared to those who didn’t pack fat around their midsections.
Researchers say the increased risk applies even to people who are otherwise normal weight, but have central obesity.
The study showed that the risk of death could be elevated even in people who don’t look very big.
“The waist might not be too large, but the distribution might still be abnormal,” says study researcher Francisco Lopez-Jimenez, MD, director of the cardiometabolic program at the Mayo Clinic in Rochester, Minn.
About 40% of the people in the study were considered normal weight, with a body mass index (BMI) under 25.
In these normal-weight patients, risks were elevated at waist sizes as small as 33 inches for men and 31 inches for women, if they also stored more fat around their midsections compared to their hips.
“A good chunk of the patients had a waist circumference that would be considered normal by all means, but the waist-to-hip ratio was abnormal,” says Lopez-Jimenez. “People tend to say if the BMI is fine, if the waist circumference is normal, then don’t worry about it. Well, if somebody is very skinny but the distribution of fat is abnormal they are at increased risk.”
Dangers of Abdominal Obesity
A growing body of evidence suggests that fat that’s stored in the abdomen may elevate the risks for heart disease, diabetes, and a host of other metabolic problems, including polycystic ovary syndrome in women, which is a cause of infertility.
“Abdominal fat is known to be more metabolically active than subcutaneous fat, the fat under the skin,” says Lopez-Jimenez.
Belly fat produces inflammatory chemicals and releases free-fatty acids into the blood. It also contributes to insulin resistance.
“That’s a fat that has been linked to high blood pressure, has been linked to diabetes, abnormal cholesterol, triglycerides,” Lopez-Jimenez says. “People with more visceral fat also tend to accumulate more fat in the liver.”
Thicker Waistlines and Heart Disease
Researchers sifted through the medical literature to find studies that focused on measures of central obesity -- waist circumference and waist-to-hip ratio -- and the risk of premature death in patients with heart disease.
Six studies, representing 15,923 patients from the U.S., France, Denmark, and Korea, were included in the final analysis.
The average age of study participants was 66. There were more men than women included in the study, 59% and 41%, respectively.
All participants had been diagnosed with coronary artery disease, which was defined as a previous history of heart attack or a procedure to open blocked arteries, like angioplasty or heart bypass. The minimum follow-up was six months.
There were 6,648 people in the normal-weight group, which was composed of people with BMIs that ranged from 18.5 to 24.9.
There were 2,396 in the obese group, who had BMIs over 30.
Across the different studies, participants were followed from six months to 16 years, with the midpoint follow-up at 2.3 years; 5,696 people died.
After adjusting their data to control for the influence of other things known to influence death risk, like age, gender, smoking, diabetes, high blood pressure, and heart failure, researchers found that those with the highest waist-to-hip ratios were, on average, about 70% more likely to have died during follow-up than those with less belly fat. Those with a high waist circumference were about 30% more likely to have died during follow-up.
Researchers estimated that abdominal obesity was responsible for about one in three deaths in the study. Among normal-weight study participants, central obesity appeared to explain about one in five deaths in men and about half of deaths in women.
Researchers say they aren’t sure why having more belly fat appears to be worse for women than men, but they can make some guesses.
“Women tend to have wider hips than men, which we think is generally protective,” says Lopez-Jimenez, “so I think for a woman to have an abnormal waist-to-hip ratio is because the constitution is quite different than her peers,” he says.