(CNN) The associations between vaping cannabis and respiratory health symptoms haven't been fully known before — but one new study has revealed a key discovery.
The study, which published Tuesday in the journal JAMA Network Open, found that vaping cannabis at any frequency was linked with symptoms of bronchitis and wheezing in young adults around 19 years old.
Toward the end of 2019, mysterious cases of lung injury associated with using e-cigarettes or vaping products — described by the US Centers for Disease Control as EVALI (which stands for e-cigarette or vaping product use-associated lung injury) — broke out.
More than 2,800 people from all 50 states, Washington DC, Puerto Rico and the US Virgin Islands had been hospitalized for or died from EVALI by mid-February of 2020, according to the CDC.
That was shortly before the spread of coronavirus, which can also harm a person's respiratory health if that person gets infected with coronavirus and then develops the respiratory disease Covid-19.
"With (Covid-19) happening, we just kind of knew that people who had vaped nicotine or had vaped cannabis were presenting a unique respiratory illness that wasn't really well understood," said the study's first author Jessica Braymiller, a postdoctoral researcher at the Tobacco Center of Regulatory Science at the University of Southern California.
"The pandemic has really underscored the importance of understanding what could make respiratory symptoms worse."
Since lungs are one primary organ severely affected by the virus, people who smoke and vape may be at higher risk for serious illness and death from Covid-19, health experts have said.
In an online questionnaire for the current study, more than 2,000 young adults who had recently graduated from Southern California high schools reported their history of vaping and smoking behaviors, and respiratory health symptoms.
Participants who had vaped cannabis any number of times from within the last month to their overall lifetime had a stronger link to symptoms of bronchitis (daily cough, congestion and phlegm) in comparison to people who had never vaped cannabis. The more times those participants had vaped cannabis in the last month, the stronger the risk was.
Vaping cannabis on three or more days in the past 30 days was associated with twice the risk of wheeze, and with experiencing whistling in one's chest during the past year — which is a high-pitched sound that, when heard while breathing, can indicate that your airways have narrowed or become inflamed. However, there were no significant associations between vaping nicotine and wheeze.
The study "continues to show the findings that inhalation leads to airway inflammation manifested" as cough, mucus and wheeze, Dr. Albert Rizzo, chief medical officer of the American Lung Association, told CNN in an email.
"More research is needed to determine if these relatively short term observations are harbingers of chronic changes and the development of chronic lung diseases," Rizzo, who wasn't involved in the study, said.
The study "makes a good effort" at trying to identify the risks of the types of inhaled exposures, Rizzo said — but there are a lot of potential differences in terms of the quality and quantity of devices people use, the ingredients and how long people vape.
For example, some aerosolized forms of cannabis oil, such as those that are more concentrated, are more likely to cause respiratory health issues when inhaled.
Different ways of vaping can increase the dose and exposure a person receives from whatever they are vaping.
And vitamin E acetate — an additive in some THC-containing e-liquids linked with e-cigarette and vaping-associated lung injuries of the 2019 outbreak — could have been present in the THC that some participants vaped, the study said. THC is tetrahydrocannabinol, the main psychoactive ingredient in cannabis.
The authors didn't have these details in their study — but said that longer studies on the links between cannabis vaping and respiratory symptoms, and on people who vape cannabis or nicotine only, are needed.
"The main takeaway is that using any kind of e-cigarettes has adverse effects for teenagers' health. Particularly so for putting cannabis in e-cigarettes," said Thomas Wills, professor and director of the Cancer Prevention in the Pacific Program at the University of Hawaii Cancer Center.
"Using cannabis obtained from illicit sources raises" the additional risk of developing EVALI, Wills, who wasn't involved in the study, added.
Although EVALI cases have declined, Wills said "cases are still being noted among young people and a lot of these patients have to be put on ventilators. This is really something you don't want."
There are a lot of scientists who still don't know about the effects of vaping on lung health, "whether it is nicotine or cannabis products," Rizzo said.
"The best course of action to benefit your health is to refrain from the use of any tobacco products since we have abundant data on its health effects ... the answers are not in as yet regarding the long term effects of vaping cannabis products."
Why vaping cannabis or nicotine would maybe cause different symptoms isn't yet fully known, USC's Braymiller said. But "it could be that the chemical constituents of the e-liquids are different."
"When you vape anything really, there's this e-liquid that is in the device that is heated up and aerosolized and then inhaled," she added. "There could be chemical differences in nicotine e-liquids versus cannabis e-liquids. And we would need more of toxicology or chemical studies to understand those differences a little bit better."
All things considered, if you're concerned about your health, "you should not vape," Rizzo said. "Per the CDC, it is felt that individuals who smoke and possibly vape, might be at risk for increased complications if COVID-19 infection occurs."
You should be aware of or monitoring for other symptoms such as fever, fatigue and loss of smell, he added, which could help you determine whether you should be tested for a coronavirus infection.
Parents of youth who use cannabis should "subtly" ask their children whether they are smoking combustible marijuana or including cannabis in e-cigarettes, Wills said.
"Any individual that has or develops the above symptoms, especially in this time of COVID-19, should discuss the symptoms with their health care provider," Rizzo said.