Could Higher BMI Have Protective Effects for the Heart?

Decades of evidence have established a link between high body mass index (BMI) and heart disease, but a new study in Mayo Clinic Proceedings suggests that higher BMI may actually have protective effects for the heart.

“Obesity has been considered a risk factor for the worst clinical outcomes following cardiovascular procedures like percutaneous coronary intervention and coronary artery bypass graft,” says lead study author Abhishek Sharma, MD, a cardiology fellow at the State University of New York Downstate Medical Center in Brooklyn, NY. “However, our results suggest that higher BMI has a protective effect after coronary revascularization procedures.”
_________________________________________________________________________________________________________________________________________________________________

RELATED CONTENT
New Study Questions “Obesity Paradox”
Obesity Paradox Called into Question
_________________________________________________________________________________________________________________________________________________________________

Sharma and his colleagues performed a meta-analysis of 36 studies that looked at the outcomes of patients with coronary artery disease who underwent coronary revascularization procedures, including percutaneous coronary intervention (PCI) and coronary artery bypass graft (CABG).

They wanted to investigate the relationship of BMI with the rates of total mortality, cardiovascular mortality, and myocardial infarction after these procedures.

After a mean follow-up period of 1.7 years, the data showed that:

• Underweight patients (BMI less than 20kg/m²) had a 1.8- to 2.7-fold increased risk of heart attack and all-cause and cardiovascular mortality.

• Overweight patients (BMI of 25kg/m² to 30kg/m²) had the lowest cardiovascular mortality risk.

• Obese patients (BMI of 30kg/m² to 35kg/m²) had a 27% lower risk of all-cause mortality than those with a normal BMI (20kg/m² to 25kg/m²).

• Severely obese patients (BMI higher than 35kg/m²) had a 22% lower risk of all-cause mortality.

At this stage, Sharma says they can only speculate reasons for this paradox. “One explanation may be that overweight patients are more likely to be prescribed cardioprotective medications, such as beta blockers and statins, and in higher doses than the normal-weight population,” he says. “Further, obese and overweight patients have been found to have large coronary vessel damage, which might contribute to more favorable outcomes. This population may have a higher metabolic reserve, which might act protectively in chronic conditions like coronary artery disease.”

Additionally, he suggests that there could be a difference in the pathophysiology of cardiovascular disease in over- and underweight patients, and that a non-modifiable genetic predisposition may also play a role in underweight patients having the highest risk of total mortality, cardiovascular mortality, and myocardial infarction.

Sharma and his colleagues are conducting further studies to investigate the existence of this paradox in various other cardiovascular diseases and different patient populations. They also plan to take a deeper look at this association and explore potential underlying mechanisms in upcoming prospective studies.

—Colleen Mullarkey

Reference

Sharma A, Vallakati A, Einstein AJ, Lavie CJ, Arbab-Zadeh A, Lopez-Jimenez F, et al. Relationship of body mass index with total mortality, cardiovascular mortality, and myocardial infarction after coronary revascularization: Evidence from a meta-analysis. Mayo Clin Proc. 2014 Jul 8. pii: S0025-6196(14)00384-X. [Epub ahead of print]