A new study reveals that one in three young adults may be at risk for severe COVID-19 complications, and smoking appears to be a major contributor to that risk. Researchers from the University of California, San Francisco studied more than 8,000 participants between the ages of 18 and 25 and found that 32% of the total study population was medically vulnerable to severe illness with COVID-19. They published their findings in the Journal of Adolescent Health.

But, according to CNN, that percentage dropped dramatically to only 16% when those who smoked either cigarettes or e-cigarettes were factored out of the analysis, thus dropping medical vulnerability in that age group by half.

“Recent evidence indicates that smoking is associated with a higher likelihood of COVID-19 progression, including increased illness severity, ICU admission or death,” Sally Adams, lead author of the study, said in a press release. “Smoking may have significant effects in young adults, who typically have low rates for most chronic diseases.”

According to the study, white adults in the 18-25 age category had the greatest vulnerability to COVID-19.

“Our finding of lower medical vulnerability of racial/ethnic minorities compared with the white subgroup, despite controlling for income and insurance status, was unexpected,” said the authors. They pointed out that their results contradict many studies showing that racial and ethnic minority groups are at greater risk for illness and death from the coronavirus.

The New York Times reported that Dr. Jonathan Winickoff, director of pediatric research at the Tobacco Research and Treatment Center at Massachusetts General Hospital, warned that smoking and vaping can exacerbate the symptoms of COVID-19 and urged smokers to stop. He said that bringing cigarettes or other devices to your mouth increased the risk of infection. He added that smokers often cough more often. “That’s a recipe for increased spread,” he told the Times.

Studies have demonstrated that smoking weakens the immune system as well as damages lung function. While research on vaping is limited, some studies suggest it causes inflammation in the lungs.