Being overweight or obese is usually considered a risk factor for heart disease. But overweight or obese heart disease patients may not be the ones most at risk of dying from a heart condition.
A recent study found that after procedures to restore blood flow in the coronary arteries, the risk of death from any cause, of death from heart disease and for heart attack was highest among patients who were underweight.
The researchers also discovered that the overweight and obese patients were less likely than patients of normal weight to die from heart disease.
The lead author of this study review was Abhishek Sharma, MD, from the Department of Medicine at Maimonides Medical Center in Brooklyn, New York.
The researchers reviewed 36 previously published studies on the risk of all-cause death, of death due to heart disease and for heart attacks after coronary revascularization procedures. These researchers separated patients by body weight or other estimates of body fat distribution.
Coronary revascularization is the process of restoring blood flow to the heart by removing or going around blockages in the coronary arteries, which provide oxygenated blood to the heart.
The studies were all published before July 31, 2013.
Follow-up periods in the various studies the authors reviewed ranged from less than a month to seven years, with an average period of two years. Each study had between 164 and 95,435 participants.
The researchers split the participants into categories according to their body mass index (height-to-weight ratio) for analysis.
The researchers set up the categories as follows: a body mass index (BMI) of less than 20 kilograms per square meter was considered underweight; between 20 and 24.9 kilograms per square meter was normal weight and used as the reference group; between 25 and 29.9 kilograms per square meter was overweight; between 30 and 34.9 kilograms per square meter was obese; and a BMI of 35 kilograms per square meter or more was considered severely obese.
The findings showed that the underweight participants had the highest risk for all-cause death, for death due to heart disease and for heart attack.
The authors of this study determined that those in the underweight category were 2.59 times more likely to die from any cause after undergoing a revascularization procedure than participants in the normal weight category.
Those who were overweight, obese or severely obese had reduced risks of death due to any cause.
According to the data, the overweight participants had a 28 percent reduced risk, the obese participants had a 27 percent reduced risk and the severely obese patients had a 22 percent reduced risk of dying due to any cause after having revascularization surgery.
Dr. Sharma and his colleagues determined that the underweight participants were 2.67 times more likely to die from heart disease after revascularization than participants of normal weight.
The overweight participants had a 19 percent decreased risk of death due to heart disease compared to the normal weight participants. The obese and severely obese participants’ risk was not affected.
The findings also showed that those who were underweight were 1.79 times more likely than the normal weight participants to have a heart attack after undergoing revascularization.
The overweight, obese and severely obese participants did not have an increased or decreased risk of heart attack, the researchers reported.
"At this stage we can only speculate on the reasons for this paradox," Dr. Sharma said in a press release.
"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. 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," Dr. Sharma said.
"Also, there could be a difference in the pathophysiology of cardiovascular disease in over- and underweight patients. A non-modifiable genetic predisposition may also play a role in underweight patients," he said.
This study was limited by a lack of data on participants’ co-occurring conditions, risk factors and the degree of heart disease in some of the studies.
Also, not all of the studies measured weight the same way, and the average follow-up time was relatively short.
This study review was published July 16 in Mayo Clinic Proceedings.
The Victoria and Esther Aboodi Assistant Professorship provided funding via grants given to Andrew J. Einstein, MD, PhD, FACC.