Being obese or overweight has been associated with greater risk of coronary heart disease and stroke compared to individuals of normal weight. It has not always been clear to what degree this greater risk is a result of medical conditions associated with obesity such as high blood pressure, high cholesterol, or diabetes, compared to the impact of being overweight or obese when the risks associated with these other health conditions are taken into account.
To answer this question, a team of researchers conducted an extensive review of 97 studies that followed individuals over time, which included a total of 1.8 million participants. Pooling these studies, the researchers determined the hazard ratios for the range of factors that could contribute to heart attacks and strokes in overweight and obese populations. Before taking into account the impact of high blood pressure, cholesterol, and glucose (a marker for diabetes), each increase of 5 kg./m2 (approximately 1 lb./ft2) of body mass index (BMI) was associated with a 27 percent greater risk for coronary heart disease and an 18 percent increase in risk for stroke. Once these other three factors were taken into account, the risk associated with each increase of 5 kg./m2 in BMI was associated with a 15 percent increase in risk of coronary heart disease and a 4 percent increase in the risk of stroke. This suggests that 46 percent of the risk of coronary heart disease for the overweight or obese is related to these three factors, and that 76 percent of stroke risk is related to these factors. Of these three factors, high blood pressure accounted for the greatest amount of this risk, accounting for 31 percent of the extra risk for coronary heart disease and 65 percent of the extra risk of stroke. The percentage of excess risk for these factors did not differ between individuals in Asia, Europe, or North America.
Looking at being overweight and obese separately, 50% of the added risk of being overweight on coronary heart disease was associated with high blood pressure, high cholesterol, or high glucose, and these factors were associated with 98 percent of the added risk for stroke. However, for obese individuals, only 44 percent of the risk of coronary heart disease and 69 percent of the risk of stroke was accounted for by these three factors.
Taken together, these findings led the researchers to conclude that, although addressing high blood pressure, cholesterol, and diabetes can address about half of the excess risk of coronary heart disease and three-quarters of the excess risk of stroke, the interventions with the greatest benefits will be those that focus on maintaining a healthy body weight. This is particularly the case for obese individuals, for whom these three factors contribute to a smaller proportion of the risk of coronary heart disease and stroke. Unfortunately, the success of interventions designed to maintain optimal body weight has been limited compared to the more effective clinical and lifestyle interventions that address blood pressure and cholesterol levels. However, while obesity and its treatment remains a major public health challenge, control of blood pressure and high cholesterol can substantially lessen the effects of the global obesity epidemic.
The Global Burden of Metabolic Risk Factors for Chronic Diseases Collaboration (BMI Mediated Effects). 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. The Lancet. (2013). DOI: 10.1016/S0140-6736(13)61836-X