Rap star Heavy D died unexpectedly last week at 44 from what looked to be, according to his cousin, a “touch of pneumonia,’’ which had been diagnosed by a doctor the day before he collapsed in front of his Beverly Hills, Calif., home. “He had what appeared to be like flu-like symptoms,’’ Ed Winter, from the Los Angeles County Coroner’s Office, told the New York Daily News. “He was taking medication, so we want to see what the levels were.’’

Although the autopsy of Heavy D, whose real name was Dwight Arrington Myers, was completed on Wednesday, the coroner’s office declined to release a cause of death until a toxicology report had been completed.

Heavy D’s excessive weight, however, was likely to have played a role in his early death. Weighing in at 344 pounds when he died, Heavy D was morbidly obese, which made him more susceptible to a host of health problems - not just the likely culprits such as heart disease, diabetes, and liver disease.

If pneumonia does indeed turn out to be the cause of death, obesity would have to be listed as a contributor, according to Dr. Benjamin Suratt, associate division chief of pulmonary and critical care medicine at the University of Vermont/Fletcher Allen Health Care hospital. “We really do believe obesity makes people do worse with lung diseases,’’ he said, “and we’re now sorting out why that is.’’

During the H1N1 pandemic, obese individuals were more likely than thinner folks to die from the flu virus or develop severe respiratory complications. “Obesity really blunts the body’s ability to cope with these sorts of lung infections,’’ Suratt said.

His own research examining the immune systems of obese mice found that certain white blood cells act sluggish in the presence of foreign invaders compared with how they act in mice who are not overweight. And the fat animals were more likely to die of pneumonia after being infected with the bacteria, which multiplied unchecked by the immune system.

That same scenario plays out in hospitals throughout the country, where overweight patients face a higher risk of both contracting pneumonia during a hospital visit and of dying from the condition if they are admitted with it.

Besides lazy immune cells, other factors appear to play a role in what researchers have found to be a complex interplay between body weight and respiratory illness. As weight increases, Suratt explained, fragile lung tissue gets compressed into a smaller volume due to increased pressure from fat tissue in the chest wall. These smaller lungs are less capable of fending off viruses and bacteria - especially when they are nearly flattened completely when an obese patient lies in bed.

“If Heavy D died of a garden-variety pneumonia,’’ said Suratt, “it could be that he wasn’t able to fight it off due to his lungs not being able to fully expand and his immune system not having been fully functional.’’

While the rapper’s actual cause of death may not be known for several weeks, the one-third of Americans who are obese could benefit from more research into the processes by which excess body weight interferes with the body’s ability to fend off infections. “We don’t know if we should lower the threshold for admitting obese patients into intensive care units,’’ Suratt said, “or whether they’d benefit from different antibiotics or different doses.’’

Oddly, though, obese patients are actually better able to fend off life-threatening emergency complications that can sometimes result from lung infections, such as acute respiratory distress syndrome or septic shock. “We all assumed they wouldn’t when we started studying this three years ago, but we were surprised to see those at the extreme end of obesity were more likely to recover from these things than someone who was moderately overweight,’’ said Suratt, or someone who is at a healthy weight.

That said, the risk of the infection itself far outweighs the added protection against rare complications, so those at or close to a healthy weight still have far better odds of beating a lung infection than those who are obese.