Does Being Underweight Increase Your COVID-19 Risk?

Everybody knows that being obese puts a person at higher risk of COVID-19 complications. This is why people above a certain BMI are given priority for monoclonal antibody treatments, according to the U.S. Department of Health and Human Services (HHS). The Centers for Disease Control and Prevention (CDC) notes that obesity triples a person's risk of COVID-related hospitalization, which may be because obesity hinders immune function and lung capacity. In fact, nearly one-third of COVID-related hospitalizations have been attributed to obesity.

A far less common discussion is whether being below a healthy weight can put a person at risk for COVID-19 complications. Part of this may be because being underweight is a relatively uncommon problem, affecting only 1.5% of American adults (per CDC). This is definitely rare, considering two-thirds of American adults are above a healthy weight (per NIH), but that doesn't mean underweight people are any less vulnerable to COVID-19.

A March 2021 study (via CDC) of nearly 150,000 American adults with COVID-19 found that the best outcomes were seen in people at the higher end of a healthy weight. The worst outcomes were reported in people with obesity, but underweight people didn't have the lowest risk, either. Underweight COVID-19 patients were 20% more likely to be hospitalized compared to patients with a healthy weight. This increase was particularly pronounced among patients younger than 65, for whom being underweight increased hospitalization risk by 41%. According to the CDC, this association may be due to undetected medical conditions, insufficient nutrients, or lowered immune response.

An English study published in The Lancet reinforced these findings, and added that frailty could be another reason underweight people are more likely to be hospitalized for COVID-19. Even when hospitalized, a recent Chinese study (via Frontiers in Nutrition) found that underweight patients were more likely to get secondary infections.

After coming to similar conclusions, the authors of a Korean study (via PLOS One) argued that COVID-19 joins cardiovascular disease as a reason it is so important for people to try to maintain a healthy weight.