Traditional risk factors fail to explain over half of CHD risk in overweight people

Traditional risk factors fail to explain over half of CHD risk in overweight people

11 September 2007

MedWire News: Blood pressure and cholesterol levels explain less than half of the excess risk for coronary heart disease (CHD) in people who are overweight or obese, results of a meta-analysis suggest.

"This implies that, even under the theoretical scenario that optimal treatment would be available against hypertension and hypercholesterolemia in overweight persons, they still would have an elevated risk of CHD," say the researchers.

Writing in the Archives of Internal Medicine, Rik Bogers (National Institute for Public Health and the Environment, Bilthoven, The Netherlands) and colleagues list several mechanisms that could contribute to the increased CHD risk in overweight people.

These include low-grade inflammation, endothelial dysfunction, a tendency toward coagulation, and left ventricular hypertrophy.

"Obviously, overweight is associated with increased risk of Type 2 diabetes mellitus," they add.

The findings emerge from a collaborative meta-analysis involving investigators from 31 prospective cohort studies, including large studies such as the Nurses' Health Study, the Norwegian Counties Study, and the Whitehall Study.

This provided data on 302,296 people who suffered 18,000 CHD events. CHD risk was assessed in relation to body mass index (BMI) categories for 14 cohorts and in relation to BMI as a continuous variable for 21 cohorts.

Overweight people (BMI 25.0-29.9) had a relative risk for CHD of 1.32, compared with normal-weight people, after accounting for age, gender, physical activity, and smoking status.

The corresponding relative risk in obese people (BMI ≥30.0) was 1.81.

Accounting for blood pressure and cholesterol levels reduced the relative risks for CHD to 1.17 and 1.49 for overweight and obese people, respectively, compared with normal-weight people.
Thus, blood pressure and cholesterol levels accounted for 47% and 40% of the excess CHD risk associated with overweight and obesity, respectively.

Each 5-unit increase in BMI increased CHD risk 1.29 fold before accounting for blood pressure and cholesterol levels, and 1.16 fold after allowing for these risk factors.

"Even moderate overweight is associated with increased risk of CHD," the researchers stress.

"Because high blood pressure and cholesterol levels are plausible intermediary factors in the causal pathways linking overweight and CHD, adjusting for them in epidemiological analyses certainly results in underestimating the total public health impact of overweight."

Arch Intern Med 2007; 167: 1720-1728