Overweight and obese patients are less likely to die in hospital after a heart operation than patients who are a normal weight, according to a study published in the journal Circulation and led by researchers from the University of Leicester.

Researchers funded by the British Heart Foundation (BHF), collected data about 401,227 adults in the UK and Ireland who had undergone cardiac surgery between 1st April 2002 and 31st March 2013.

Patients’ body mass index (BMI) was categorised into six groups; underweight (BMI under 18.5 Kg/m2), normal weight (BMI 18.5–25), overweight (BMI 25–30), obese class I (BMI 30–35), obese class II (BMI 35–40), and obese class III (BMI over 40).

When they looked at how well these patients fared in hospital after their surgery the team, at the University of Leicester, found that overweight and obese patients were less likely to have died than patients who were a normal weight, while patients who were underweight had a higher risk of dying.

Overall, 11,511 patients died whilst in hospital. 4.4 percent of patients of normal weight died, whereas only 2.8 percent of overweight and 2.7 percent of obese class I patients died whilst in hospital. The analysis also showed that 8.5 percent of patients who were underweight died.

The researchers also allowed for factors that might influence the results – such as the likelihood that only younger obese patients, or those with fewer pre–existing medical conditions, would have been offered operations, meaning that they would also be more likely to survive. However, the analysis found that older obese patients, and those with complications of obesity, including hypertension, diabetes and coronary artery disease, had greater protection.

The researchers also reviewed data from 557,720 further patients included in studies across Europe, the United States and Asia, finding similar results.

Now, the team hope to go on to look at how exactly being overweight or obese protects patients who undergo surgery.

BHF Professor Gavin Murphy, BHF Professor of cardiac surgery at the University of Leicester, said: “Obesity is a reason often given for not offering patients surgery. With this study we show that, for cardiac patients at least, being obese should not be a reason to turn patients away from surgery.”

“These results also raise questions as to whether there may be attributes of obesity that directly protect patients. Understanding these processes may open the door to new prevention strategies or treatments.”

Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation, said: “Survival rates for heart surgery are now extremely high, thanks to many years of research.

“We always recommend a healthy waistline, which significantly reduces lifetime risk of heart disease and therefore a person’s risk of needing cardiac surgery. However, this large study strongly suggests that being overweight can give patients added protection when facing major heart surgery, reducing their chance of complications or death before leaving hospital.

“To properly understand why, we need to fund more research in to the mechanisms involved. This could lead to new strategies to improve survival rates in normal and underweight patients following surgery.”

Whilst this study is the largest of its kind looking at the link between obesity and surgery survival rates, it only looked at the survival rates of patients whilst they were still in hospital and cannot therefore be used to predict the long–term survival of surgery patients.