New research suggests obesity may be a factor in the transmission of the influenza virus.
In a study conducted in Managua, Nicaragua, obese adults spread the influenza virus for significantly longer than non-obese individuals. The findings have significant ramifications, given that worldwide obesity has nearly tripled since 1975, according to the World Health Organization.
Epidemiologist Aubree Gordon at the University of Michigan started looking into the correlation between obesity and the flu nine years ago. Gordon explained that "during the 2009 influenza pandemic, it became quite clear that obese individuals were at higher risk for severe influenza. And more recently, some studies have shown that obese individuals don't respond as well to the influenza vaccine."
Gordon collaborated with the Nicaraguan Ministry of Health on a three-year research program that followed 1,783 individuals in 320 households. The researchers visited homes where at least one member reported symptoms of influenza. Researchers collected samples every few days for two weeks, tracking infected individuals and others in the home who agreed to enroll in the study.
When Gordon and her colleagues analyzed the samples, they found that obese adults shed the influenza virus 42 percent longer than non-obese adults — or about a day and a half longer period of shedding the virus.
Weaker immune system
Previous research found that obesity led to chronic inflammation and a poorer functioning immune system. Will Green, a doctoral candidate at the University of North Carolina's School of Public Health who was not involved in the study, explained how the immune system works to combat the virus.
"There's an innate first responder. They're the ones that immediately show up to fight. And then there's the adaptive T- and B-cell memory response. You need both pieces, but the adaptive response is really the one that's been shown to be impaired in obesity," Green said.
Because obese people have a weakened immune system, there were concerns that the obese people in the study were shedding more of the virus simply because they were sicker. However, scientists imposed strict controls by studying only those adults who were infected but had few symptoms.
"In people who were either asymptomatic — having no symptoms — or just had one minor symptom, obese adults still shed for significantly longer than non-obese adults," Gordon said. "In fact, they shed [viral DNA] for about twice as long.
"I think this is another piece of evidence that obese individuals really have an altered immune system, and they're having trouble potentially clearing the infection, which could lead to higher severity," Gordon added.
Nikhil Dhurandhar, chair of nutritional sciences at Texas Tech University, cautions that further research is needed. He told VOA that scientists still don't understand how much the duration of viral shedding is linked to infection rates.
"Is it a huge amount of virus that is getting excreted? Is it very little?" Dhurandhar asked. "And also, what we don't know is how infectious that is."
Green also noted that if shedding the virus means that obese people either remain sick or infectious longer, "you can also equate that to the greater loss of work time and higher health care costs."
Gordon and her colleagues' study, published in The Journal of Infectious Diseases, highlights a risk of obesity that isn't going away anytime soon.
As Gordon told VOA, "Obesity is a growing epidemic, unfortunately, and becoming a huge problem worldwide."