Diacetyl - A Critical Safety Review of the Science Defining the Environmental Inhalation Hazards Association with Chronic Lung Disease

Abstract

In the last two decades scrutiny of several retrospective occupational studies on performed by NIOSH in the early 2000’s on ambient indoor air exposures to the flavoring chemical diacetyl and more complex butter flavoring formulations has led to a reported association between diacetyl and severe irreversible lung disease, primarily bronchiolitis obliterans. A group of laboratory rodent studies, performed primarily by associated researchers, followed in the next two decades with the intent to determine a plausible physiological mechanism for bronchiole scarring applicable to the human respiratory tract. Recently, a renewed interest in diacetyl as a flavoring constituent of vaping liquids and marijuana and inhalation exposures has emerged. This paper reviews the universe of published literature to date in relation to whether diacetyl or butter flavors containing diacetyl causes occupational or environmental lung disease, more specifically BO (i.e., general causation) and whether specific levels of inhaled diacetyl or butter flavors containing diacetyl are associated with chronic lung disease. The review included numerous journal articles, government reports, etc. Based upon the evidence, while the literature reflects a statistical association between both diacetyl and butter flavoring diacetyl mixtures and lung disease, there is sufficient evidence to conclude that general causation between exposure to diacetyl concentrations measured in the ambient air environments studied to date and chronic lung disease does not exist.