A new study in a number of states in America has established a direct link between legalisation of cannabis sativa consumption and rising incidence of asthma, especially in children and young adults.

About six million children in the United States have asthma, according to the US Centers for Disease Control and Prevention.

The study found that Black and Hispanic children in the United States are at significantly higher risk of developing asthma than white children.

Boys under the age of 13 have an increased prevalence of asthma than girls of the same age.

A study by researchers at the Columbia University Mailman School of Public Health and The City University of New York noted an increase in the prevalence of asthma among older children in states where lawmakers have made the recreational use of cannabis legal.

This study, according to its authors, is the first to look at the changes in laws regarding cannabis at the state level and the incidence of asthma in children. The researchers’ findings were published in the journal Preventive Medicine.

“No one has really written anything or done any studies on this,” Renee Goodwin, an adjunct associate professor in the department of epidemiology at Columbia Mailman School of Public Health, a professor at The City University of New York, and a co-author of this study, told Medical News Today.

For their study, the researchers used data from the National Survey on Children’s Health (NSCH), a representative sample of the population of minor children in the United States.

The researchers used NSCH data to compute the prevalence of caregiver-reported paediatric asthma. Figures were made for the years 2011-2012, 2016-2017 and 2018-2019.

The sample consisted of 227,451 US children. The mean age was slightly more than 8. Of the children, nearly 51 per cent were male and nearly 60 per cent were identified as non-Hispanic white, nearly 17 per cent as Hispanic, and 12 per cent as non-Hispanic Black.

The researchers computed that the prevalence of pediatric asthma was nearly 9 per cent in 2011-2012. That number dropped to 8 per cent in 2016-2017 and to 7.8 per cent in 2018-2019.

“Overall, while reductions were generally greater in states without cannabis legalisation or with recent [legalization of medical marijuana], the rate of reductions were not statistically different by [whether or not a state had legalised recreational use or medicinal use of cannabis],” the researchers write in the paper about their study.

Among youth ages 12 to 17, the prevalence of asthma increased in states with cannabis legislation, particularly in states that had legalised the recreational use of marijuana.

Overall, increases in pediatric asthma were significantly greater among children who identified as non-Hispanic minorities in states where cannabis was legal for recreational and medicinal use compared to states where cannabis is not legal.

The greatest increase in pediatric asthma overall in states where the recreational use of cannabis is legal is among Hispanic youth. The researchers caution in the paper that their findings do not establish a direct link between marijuana laws and increases in the prevalence of pediatric asthma.

Dr Brian Christman, a volunteer spokesperson for the American Lung Association and professor and vice-chair for clinical affairs and associate programme director for the Medicine Residency Program at Vanderbilt University in Tennessee, pointed to the declining numbers of the prevalence of pediatric asthma shown in the study.

He attributes the change, in part, to public health work around cigarette smoking and second-hand smoke.

“What it’s telling us is that that we’ve done a great job on tobacco control,” he told MNT. “And so across the line, in most states, asthma prevalence in kids has just been going down, which is great.”

The fact that the prevalence of asthma increased among youth ages 12 to 17 in states with cannabis legislation reflects that “apparently, it’s being used in the home around adolescent children who have the higher incidence of asthma in the paper, and this is irritating their airways.”

Christman stressed that the study, which he was not involved in, had a large number of participants.

“The numbers are not massive, but when you see a couple of percentage changes and you’re talking about hundreds of thousands of people, it’s probably important,” he said.

Goodwin told MNT she undertook this study because she noticed how quickly different states were moving to legalise the recreational use of marijuana, despite the fact that she feels there needs to be more and better public health messaging regarding cannabis.

“There’s a perception that cannabis smoke is different from or harmless compared to cigarette smoke,” she said.

Goodwin pointed out that pediatricians have a checklist of questions they should ask about children’s homes. However, the list doesn’t include a question about whether or not anyone in the home smokes cannabis indoors, she said.

“There is no guidance for parents and there’s no guidance for clinicians,” Goodwin said.

Parents who smoke cannabis are better off smoking outside, Christman told MNT.

“To be considerate of your family, particularly with children when they have growing and developing lungs,” he said. “Or you can have long-term effects by this kind of exposure.”

A 2021 study, where Goodwin also served as a co-author, found that in states where recreational use of cannabis is legal or where medical marijuana is legal, adults living in households with children were more likely to have used cannabis in the previous month and were more likely to use cannabis daily compared to households in states where cannabis is not legal.

The highest prevalence of cannabis use in this study was among those between the ages of 18 and 25 in states where recreational use of cannabis is legal and those who identified as non-Hispanic, Black in states with legalised recreational use.

If more parents are using cannabis, Goodwin said, they need to know whether second-hand exposure to cannabis smoke is dangerous. However, more research needs to be done on the subject, according to Goodwin.

“State legislatures are acting in the absence of scientific data,” she said.

A 2016 study did find, however, that one minute of exposure to cannabis second-hand smoke substantially impairs endothelial function (the lining of blood vessels) in rats for at least 90 minutes. Another earlier study confirmed the presence of known carcinogens and other chemicals implicated in respiratory diseases in the smoke of marijuana cigarettes.

“There is mounting data that it is not harmless and has perhaps even more harmful effects than tobacco,” Goodwin said.

Public health education has convinced some parents to go outside to smoke tobacco cigarettes because they know second-hand smoke isn’t good for kids, Goodwin pointed out.

With cannabis, the law may make going outside tricky, depending on the state. Possession of cannabis may be legal in some states, but it may be illegal to consume it in public. That could make parents reluctant to step outside their apartment building to smoke, according to Goodwin.

• A Medica News Today report