Body-mass index (BMI) and diabetes have increased worldwide, whereas global average blood pressure and cholesterol have decreased or remained unchanged in the past three decades. The authors of this paper measured how much of the effects of BMI on coronary heart disease and stroke are mediated through blood pressure, cholesterol, and glucose, and how much is independent of these factors.
They pooled data from 97 prospective cohort studies that collectively enrolled 1·8 million participants between 1948 and 2005, and that included 57 161 coronary heart disease and 31 093 stroke events. They estimated the hazard ratio (HR) of BMI on coronary heart disease and stroke with and without adjustment for all possible combinations of blood pressure, cholesterol, and glucose.
The Hazard Ratio for each 5 kg/m2 higher BMI was 1·27 for coronary heart disease and 1·18 for stroke after adjustment for confounders. Additional adjustment for the three metabolic risk factors reduced the HRs to 1·15 for coronary heart disease and 1·04 for stroke, suggesting that 46% of the excess risk of BMI for coronary heart disease and 76% for stroke is mediated by these factors. Blood pressure was the most important mediator, accounting for 31% of the excess risk for coronary heart disease and 65% for stroke. The percentage excess risks mediated by these three mediators did not differ significantly between Asian and western cohorts (North America, western Europe, Australia, and New Zealand). Both overweight (BMI ≥25 to <30 kg/m2) and obesity (BMI ≥30 kg/m2) were associated with a significantly increased risk of coronary heart disease and stroke, compared with normal weight (BMI ≥20 to <25 kg/m2), with 50% of the excess risk of overweight and 44% (41—48) of the excess risk of obesity for coronary heart disease mediated by the selected three mediators. The percentages for stroke were 98% for overweight and 69% for obesity.
They concluded that Interventions that reduce high blood pressure, cholesterol, and glucose might address about half of excess risk of coronary heart disease and three-quarters of excess risk of stroke associated with high BMI. Maintenance of optimum bodyweight is needed for the full benefits.
The Global Burden of Metabolic Risk Factors for Chronic Diseases Collaboration (BMI Mediated Effects) The Lancet, Early Online Publication, 22 November 2013
Metabolic mediators of the effects of body-mass index, overweight, and obesity on coronary heart disease and stroke: a pooled analysis of 97 prospective cohorts with 1·8 million participants