Besides increasing a person's risk for severe complications from influenza, including hospitalisation and even death, obesity might also play a role in how flu spreads, a new study has found.

The findings, published in The Journal of Infectious Diseases suggested that obese adults with flu symptoms and laboratory-confirmed influenza shed influenza A virus for 42 per cent longer than adults with flu who were not obese. "This is the first real evidence that obesity might impact more than just disease severity," said Aubree Gordon, from the University of Michigan in the US.

With rates of obesity rising around the world, the new findings, if supported by future studies, suggest that obesity may play an increasingly important role in flu transmission. Obesity can alter the body's immune response and lead to chronic inflammation, which increases with age in addition to making breathing more difficult, thereby affecting influenza risk, severity, and transmission potential, the study authors noted.

After analysing data collected from nearly 1,800 people in 320 households in Managua, Nicaragua, the team investigated the effect of obesity on the duration of viral shedding over three influenza seasons from 2015 to 2017. Among obese individuals infected with flu who were only mildly ill or had no symptoms, the difference was greater: these obese adults shed influenza A virus for 104 per cent longer than non-obese adults with flu.

However, the differences seen in the duration of viral shedding were only limited to influenza A viruses, one of two types of flu viruses that can cause epidemics in humans. Researchers found no association with obesity and the duration of shedding of influenza B virus, which typically causes less serious illness in adults and does not cause pandemics. Obesity also did not appear to impact the duration of viral shedding among children included in the study.