Warnings about the upcoming flu season seem to be adding insult to injury in the year of COVID. And yet, the familiar virus joins the unfamiliar COVID as yet another threat that could land people in the hospital.

As it turns out, poor sleep makes everyone more vulnerable to the ravages of flu. Researchers at the Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire, confirmed the danger in a recent study publicized in several media outlets such as the American Journal of Managed Care. 

Originally published in the Journal of Clinical Sleep Medicine, the study showed that adults with obstructive sleep apnea (OSA) who were not compliant with CPAP were found to be more likely to be hospitalized with influenza than those who used CPAP. 

“For the approximately 30 million American adults with OSA, disruptions in sleep caused by the condition may adversely impact immune system functioning, note the researchers,” writes Matthew Gavidia. “Amid the coronavirus disease 2019 (COVID-19) pandemic, this can have an extensive impact on risk of infection and adverse outcomes among this patient population. Moreover, the emergence of the flu season may further exacerbate this risk, as patients with OSA may require hospitalization amid surging rates of COVID-19 infection.” 

Patients conservatively treated without CPAP or nonadherent to CPAP therapy were at a nearly five-times greater risk of hospitalization than those adherent to CPAP. "These results would suggest that use of a treatment, CPAP, that improves sleep quality reduces the severity of influenza infection as determined by rate of hospitalization," said study author Glen Greenough, MD, associate professor of medicine, psychiatry, and neurology at the Dartmouth-Hitchcock Medical Center, in a statement. "This might suggest that treating sleep apnea and thereby improving sleep quality has a beneficial effect on the immune system."

Immune system benefits have indeed been touted as a major upside to OSA treatment, and while the study quoted above did not specifically track the use of oral appliances, clinicians such as Shad Morris, D.M.D., believes it stands to reason that such appliances also boost the immune response. “Whether it’s CPAP, oral appliances, or simply positional sleep therapy, treating OSA is the key common denominator,” says Morris, owner of Premiere Sleep Solutions, St. George, Utah. “These days, it’s hard to find a physiological variable that does not benefit from proper sleep.”