Being overweight may protect people from cardiovascular mortality, researchers, including one of Indian-origin, have claimed.

High body mass index (BMI) is associated with multiple cardiovascular diseases. However, emerging data suggest that there is an "obesity paradox" - that being overweight may actually protect patients from cardiovascular mortality.

Investigators have confirmed that the risk of total mortality, cardiovascular mortality, and myocardial infarction is highest among underweight patients, while cardiovascular mortality is lowest among overweight patients, according to two reports published in the journal Mayo Clinic Proceedings.

Abhishek Sharma, Cardiology Fellow at the State University of New York Downstate Medical Center in Brooklyn, New York, and colleagues conducted a meta-analysis of 36 studies.

They determined that low BMI (less than 20 kg/m2) in tens of thousands of patients with coronary artery disease who underwent coronary revascularisation procedures was associated with a 1.8- to 2.7-fold higher risk of myocardial infarction and all-cause and cardiovascular mortality over a mean follow up period of 1.7 years.

Conversely overweight and obese patients had more favourable outcomes. Cardiovascular mortality risk was lowest among overweight patients with a high BMI (25-30 kg/m2) compared to people with a normal BMI (20-25 kg/m2).

In obese and severely obese patients with a BMI in the 30-35 and over 35 kg/m2 range, all-cause mortality was 27 per cent and 22 per cent lower than people with normal BMI.

"At this stage we can only speculate on the 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," Sharma said.

In the second study, investigators led by Carl Lavie, Medical Director of Cardiac Rehabilitation and Preventative Cardiology at the John Ochsner Heart & Vascular Institute, Ochsner Clinical School, at the University of Queensland School of Medicine in New Orleans examined the "obesity paradox" from another perspective.

They evaluated the effects of body composition as a function of lean mass index (LMI) and body fat (BF) on the correlation between increasing BMI and decreasing mortality.

They estimated BF and LMI in nearly 48,000 people with a preserved left ventricular ejection fraction of more than 50 per cent and examined the survival advantages of obesity across strata of these body compositions.

This large observational study showed that higher lean body mass was associated with 29 per cent lower mortality, and while higher fat mass also exhibited survival benefits, this advantage disappeared after adjustment for lean body mass, suggesting that non-fat tissue bears the primary role in conferring greater survival.