Marijuana users have higher levels of heavy metals in blood: study

Marijuana users have elevated levels of cadmium and lead in their blood and urine compared to those who abstain, a troubling new study found.  

Analyzing data from a group of more than 7,200 adults, researchers from Columbia University Mailman School of Public Health found that the 358 people who reported using marijuana within the past 30 days had 27% higher blood lead levels, compared to those who said they refrained from both marijuana and tobacco. 

The authors found marijuana users also had 21% high urine lead levels, in addition to 22% higher blood cadmium levels and 18% higher urine cadmium levels, compared to those who didn’t use either marijuana or tobacco. 

The researchers studied data from blood and urine samples collected between 2008 and 2015 as part of the National Health and Nutrition Examination Survey, which is conducted by the National Center for Health Statistics

They separated 7,254 participants into five categories: non-marijuana/non-tobacco use, exclusive marijuana use, exclusive tobacco use, and dual marijuana and tobacco use. They then measured five different metals in the individuals’ blood and 16 in their urine.

“Because the cannabis plant is a known scavenger of metals, we had hypothesized that individuals who use marijuana will have higher metal biomarker levels compared to those who do not use,” said Katlyn McGraw, a study author and a postdoctoral researcher at Columbia University.

“Our results therefore indicate marijuana is a source of cadmium and lead exposure,” she added.

There is no safe amount of lead exposure, according to the World Health Organization. Even low levels of exposure can affect children’s brain development, resulting in behavioral and learning problems. In adults, lead exposure can lead to elevated risks of high blood pressure, heart problems and kidney damage.

Cadmium is classified as a carcinogen by the WHO and exposure, even at low levels, over time through air and water or tobacco smoke can cause kidney disease and fragile bones.

“For both cadmium and lead, these metals are likely to stay in the body for years, long after exposure ends,” Tiffany Sanchez, an author of the study and an assistant professor of environmental health sciences at Columbia University, told NBC News. 

The study’s findings were published Wednesday in the journal Environmental Health Perspectives.