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Some researchers believe people who are overweight but otherwise healthy don't have a higher-than-normal risk of heart disease. But a new report suggests extra weight can be harmful alone, regardless of whether people have a cluster of risk factors known as metabolic syndrome.
Metabolic syndrome is a group of conditions linked to heart disease. It includes a large waist circumference, high blood pressure, high triglycerides, low "good" cholesterol and diabetes.
Although each of those conditions is closely tied to extra weight, some researchers think metabolic syndrome and not the weight itself is what cause heart disease.
"There's been so much about that in the literature over the last many years, that it's only the ones with metabolic syndrome that are at risk," Dr Børge G. Nordestgaard said.
His research suggests the picture is more complicated.
Metabolic syndrome components
For their study, Nordestgaard and Dr Mette Thomsen of the University of Copenhagen recruited 71 527 Danish adults without heart problems.
The researchers weighed, measured and checked participants for the five components of metabolic syndrome.
People were considered to have metabolic syndrome if they had at least three of those conditions. 44% of the participants had a normal weight, 40% were overweight and 16% were obese when the study started.
Rates of metabolic syndrome ranged from one in ten among normal-weight people to close to two-thirds of obese participants.
Over the next three to four years, 634 people in the study had a heart attack and 1 781 were diagnosed with heart disease.
The research duo found people's chances of developing heart problems went up as their weight went up, whether or not they had metabolic syndrome.
Other contributing factors
Obese people without metabolic syndrome were almost twice as likely to have a heart attack as normal-weight people without metabolic syndrome, for instance.
The results suggest only a fraction of the extra heart risks seen among overweight and obese people can be explained by more of them having metabolic syndrome, the researchers write in JAMA Internal Medicine.
"There could be other factors in obesity and overweight that also contributes, like inflammation for example," Nordestgaard told Reuters Health. But, "I'm not saying these cardiovascular disease risk factors are not important," he said.
Blood pressure and cholesterol contribute to a person's chance of getting heart disease, Nordestgaard said. But the label of metabolic syndrome, which is used by some doctors as a clear dividing line, may not be what's critical.
"Whether you call someone as having or not having metabolic syndrome as kind of a yes/no variable, is not helpful clinically and it doesn't make sense biologically," Dr Meir J. Stampfer said.
Cumulative effect
Stampfer, from the Harvard School of Public Health, co-wrote a commentary published with the new study.
The idea that people aren't at risk unless they meet the criteria for metabolic syndrome is "really flawed", he told Reuters health."It's basically just that the metabolic syndrome is waiting to happen to those people. "Based on this study, extra weight and metabolic problems may have a "cumulative effect" on a person's risk of heart disease, Dr Jiang He told Reuters Health in an email.
He is the chair of the Tulane University School of Public Health and Tropical Medicine Department of Epidemiology in New Orleans and wasn't involved in the new study.
Researchers agreed that people should do what they can to control their weight. "Obesity is a preventable condition," he said.
Nordestgaard recommended that people who are overweight think about their diet and get more exercise to avoid future heart problems. "Any overweight or obesity puts you at increased risk of heart disease," he said.
