Nearly two-thirds of U.S. adults are overweight and therefore at higher risk for heart disease, other illnesses and death, according to background information in the article. "Because of the high prevalence of overweight and the expected future increases, it is essential to gain precise insight into the consequences of overweight for health and into the metabolic pathways that link the two," the authors write.
Rik P. Bogers, Ph.D., of the Centre for Prevention and Health Services Research, National Institute for Public Health and the Environment, Bilthoven, the Netherlands, and colleagues combined data from 21 previous studies of overweight and heart disease that included a total of 302,296 participants.
A total of 18,000 heart events or deaths occurred among these participants during the studies. After the researchers factored in age, sex, physical activity levels and smoking, moderately overweight individuals had a 32 percent increased risk of heart disease compared those who were not overweight. Obesity increased their risk 81 percent over those of normal weight.
The researchers then adjusted the figures further for blood pressure and cholesterol levels. This reduced the excess risk associated with being moderately overweight by 47 percent, to 17 percent, and with obesity by 40 percent, to 49 percent. For every five units an individual's body mass index increased, the risk for heart disease increased 29 percent before adjusting for blood pressure and cholesterol and 16 percent after adjustment.
"Hence, the present study indicates that adverse effects of overweight on blood pressure and cholesterol levels could account for about 45 percent of the increased risk of coronary heart disease, and that there is still a significantly increased risk of coronary heart disease that is independent of these effects," the authors write.
"This implies that, even under the theoretical scenario that optimal treatment would be available against hypertension and hypercholesterolemia in overweight persons, they would still have an elevated risk of coronary heart disease."
They propose several other mechanisms by which being overweight could increase the risk of heart disease, including constant low-grade inflammation, problems with blood vessel function or an imbalance in blood chemicals that could lead to more clotting.