A new study based on analysis of data from the 2007-2010 National Health and Nutrition Examination Survey (NHANES) analyzed by researchers at Emory University’s Woodruff Health Sciences Center Division of Pulmonary, Allergy and Critical Care Medicine has revealed an association between recent marijuana use and airway inflammation symptoms, but moderate lifetime use not associated with clinically significant changes in lung function. This study is described as the largest cross-sectional analysis of the relationship between marijuana use and measures of lung health to date.

NHANES is an ongoing nationally representative survey conducted through the National Center for Health Statistics. The analyzed data included survey questions and standardized spirometry — the latter a screening tool used by physicians to find and diagnose indications of pulmonary disease, and to measure lung function by measuring the volume of air an individual can expel from his or her lungs (called “forced vital capacity”, or FVC) and the volume of air forced out in the first second of the maneuver (forced expiratory volume, or FEV1).

The research results are published online ahead of print in December, 2014 in the Annals of the American Thoracic Society, and will also be published in an upcoming print edition.

The paper, entitled: “Effects of Marijuana Exposure on Expiratory Airflow: A Study of Adults who Participated in the U.S. National Health and Nutrition Examination Study“ (Annals ATS. First published online 18 Dec 2014 as DOI: 10.1513/AnnalsATS.201407-333OC ), is coauthored by Jordan A. Kempker, MD, MSc, clinical research fellow in the Division of Pulmonary and Critical Care Medicine in Emory University School of Medicine in Atlanta, Georgia, with Eric G. Honig, MD, and Greg S. Martin, MD, MSc — both also professors in Emory’s Division of Pulmonary and Critical Care Medicine.

The paper coauthors explain that their study’s objectives were to determine any association between recent and long-term marijuana smoke exposure with spirometric parameters of lung function and symptoms of respiratory health in a large cohort of U.S. adults. The study they analyzed is a cross-sectional study of U.S. adults who participated in the 2007-2008 and 2009-2010 National Health and Nutrition Examination Survey cycles, examining data from standardized spirometry and survey questions performed during these years.

They found that among the combined 2007-2010 cohorts, 59.1 percent had used marijuana at least once in their lifetime and 12.2 percent had used the drug in the past month, and that increasing frequency of marijuana usage over the prior month was associated with higher incidence of self-reported respiratory symptoms such as bronchitis (coughing, wheezing, etc.) but found no clinically significant changes in lung function as measured by spirometry.

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Moreover, among nearly 3,000 adult participants providing data regarding lifetime marijuana use patterns, cumulative exposures of fewer than 20 joint-years (one joint year = smoking an average of one joint per day for a year) were not associated with deleterious lung function changes, as measured by the FVC and FEV1.

While exposures greater than 20 joint-years were found to be associated with measurable and clinically significant lung function changes, the latter displayed a pattern different from patterns observed in persons with chronic obstructive lung disease (COPD) associated with tobacco use, and consequently are of uncertain clinical significance to overall lung health.

“While over 20 joint-years is significantly associated with a change in lung function, it is inconclusive whether or not this represents early lung function impairment similar to long-term tobacco use,” says study lead author Jordan A. Kempker in an Emory Woodruff Health Sciences Center release, who explains that the results observed may also be attributable to the relatively low volumes of smoke inhaled by marijuana smokers compared to tobacco smokers, noting that the latter cohort are generally at risk of pulmonary disease after 20 pack-years of exposure (one pack-year = smoking an average of one pack of cigarettes a day for a year) representing substantially significantly more smoke exposure than 20 marijuana joint-years.

“Furthermore, smoking marijuana seems to increase symptoms of respiratory irritation, such as bronchitis, and our study was inconclusive about whether those effects are permanent, says Dr. Kempker. “We also did not study the association of marijuana smoking with the development of cancer,”

The coauthors contend that given the inconclusive science on long-term effects of marijuana exposure on lung function, combined with increasing tetrahydrocannabinol composition of marijuana over time, and increasing legal accessibility of the herb in both medical and recreational contexts, continued investigation into these effects is needed. They conclude: that, “With current marijuana smokers reporting a mean joint-year exposure of 15.8 joint-years, these data represent important public health implications. With the shifting political climate in the U.S. these are important public health concerns that necessitate further inquiry into this growing field. Future research directions may potentially target study populations in those states in the U.S. where marijuana is now legally consumed and it will now be more feasible to longitudinally follow users consumption patterns, pulmonary function and symptoms.”

The research was supported by the National Institutes of Health.

Sources:
Emory University Woodruff Health Sciences Center
Annals of the American Thoracic Society

Image Credits:
Emory University