American Heart Association calls for more research on e-cigarettes

Research increasingly reveals the health risks associated with using e-cigarettes, and more studies are needed to understand the long-term effects of e-cigarettes on the heart and lungs, according to a new scientific statement published today in the American Heart Association's flagship journal, Circulation.

The new scientific statement, “The Cardiopulmonary Effects of E-Cigarettes and E-Cigarette Products,” details the latest usage data and trends, identifies current health impacts, highlights existing foundational and clinical scientific evidence surrounding e-cigarettes, and suggests research priorities to further understand the short- and long-term health effects of e-cigarette use.

E-cigarette products, also known as e-cigarettes, are battery-powered systems that heat liquid solutions or e-liquids to produce aerosols inhaled into the lungs. Most e-liquid formulations provide nicotine, which has been identified as having negative health effects and strong addictive properties. These products may also contain other substances, most commonly tetrahydrocannabinol (THC), the psychoactive component of cannabis, as well as methamphetamine, methadone, or vitamins. The liquids also include humectants (hygroscopic carriers such as propylene glycol and vegetable glycerin), which serve as solvents and produce water aerosols or vapor, flavorings, coolants like menthol, and metals and other chemicals from the heating coils.

E-cigarettes deliver many potentially harmful substances into the body, including chemicals and other compounds that users may not be aware of or understand. Studies have shown that nicotine-containing e-cigarettes are associated with acute changes in several hemodynamic parameters, including increased blood pressure and heart rate. Other studies have shown that even in the absence of nicotine, components in e-cigarettes, particularly flavorings, independently carry risks associated with heart and lung diseases in animals. The negative effects of e-cigarettes have been demonstrated through in vitro studies and studies of individuals exposed to chemicals in commercial products.

—Jason J. Rose, MD, MBA, Associate Professor of Medicine and Vice Dean for Innovation and Physician Scientist Development, University of Maryland School of Medicine

The writing committee emphasized the importance of the clinical diagnosis of “e-cigarette or vaping product use-associated lung injury” (eVALI). eVALI was first recognized as a disease by the Centers for Disease Control and Prevention in 2019, when approximately 2,800 e-cigarette users were hospitalized in less than a year. The statement cited this as an example to highlight the lack of knowledge regarding the risks of e-cigarettes and their components. In cases of eVALI hospitalization, vitamin E acetate was identified as a potential causative agent. This substance is used as a thickening agent in some e-liquids.

Research measuring the specific impact of e-cigarettes on heart attacks and strokes is limited. Many studies on e-cigarette use have been conducted in populations that also use or have used traditional combustible cigarettes. Additionally, large survey studies have focused on younger individuals, who have lower rates of heart attacks and strokes. The writing committee stated that long-term studies are needed on e-cigarette users of all ages, including those with existing cardiovascular diseases.

A recent analysis of the Adult Tobacco and Health Population Assessment (PATH) study found a statistically significant association between e-cigarette use reported by participants at the time of the study and the development of respiratory diseases (chronic obstructive pulmonary disease/COPD, chronic bronchitis, emphysema, or asthma) within the next two years. The PATH study is an ongoing research project that began in 2013 and is one of the first large tobacco research efforts conducted by the National Institutes of Health and the U.S. Food and Drug Administration.

Other studies cited in the statement indicate that the number of individuals who have ever used e-cigarettes or are currently using these devices has rapidly increased since 2010, with most users being current or former traditional smokers. Additionally, by 2016, data from the Behavioral Risk Factor Surveillance System indicated that approximately 10,000 adults who had never smoked combustible cigarettes were currently using e-cigarettes in the U.S.

The writing committee noted that e-cigarettes are reportedly the most commonly used tobacco product among young people, particularly high school and middle school students. The data cited in the statement indicates that nearly three-quarters of young e-cigarette users specifically report using flavored e-cigarette products. According to the statement, the high usage rates among young people make it crucial to assess the short- and long-term health impacts of these products.

“Young people are often attracted to the flavors in these products and may develop nicotine dependence from using e-cigarettes. There are significant concerns that young people perceive e-cigarettes as harmless because they are widely available and marketed to age groups that include many who have never used any tobacco products,” Rose said. “The long-term risks of using e-cigarettes are unknown, but if the risks of long-term use are similar to those of combustible cigarettes, or even if the risks are lower but still present, we may not observe them for decades. Equally concerning is that studies show some young e-cigarette users continue to use other tobacco products, and there is a correlation between e-cigarette use and substance use disorders.

Given the established high health risks of smoking combustible cigarettes, e-cigarette products have been evaluated as smoking cessation tools. The writing committee reviewed the limited research in this area and concluded that any potential benefits e-cigarettes may offer in helping people quit smoking or stop using tobacco products need to be clearly balanced against the known and unknown potential health risks of these products (including the known risks of long-term dependence on these products).

“E-cigarette companies promote their products as a way to quit traditional cigarettes. However, there is no strong evidence supporting this beyond any short-term benefits. The lack of long-term scientific safety data on e-cigarette use and the potential for young people to become addicted to e-cigarette products is one of the reasons the American Heart Association does not recommend using e-cigarettes for smoking cessation,” said Rose Marie Robertson, MD, the American Heart Association's Deputy Chief Science and Medical Officer and Co-Director of the Association's Tobacco Regulatory Science Center. “It is also important to note that e-cigarette products have not been approved by the U.S. Food and Drug Administration (FDA) for smoking cessation. The Association recommends combining multiple smoking cessation counseling sessions with FDA-approved doses and formulations of personalized nicotine replacement therapy, along with medications to help control cravings, to assist individuals in quitting combustible cigarettes. All of this needs to be understood in the context that quitting smoking often requires multiple attempts, and any failures should be viewed as learning experiences on the path to ultimately overcoming a powerful addiction.

The writing committee emphasized the urgent need for additional knowledge and research, particularly:

1. Future research should focus on obtaining knowledge about the serious and potential long-term effects of e-cigarettes on the heart, blood vessels, and lungs.

2. Research is needed on patients with existing cardiopulmonary diseases (such as coronary artery disease or COPD) to assess and compare outcomes between e-cigarette users and traditional smokers, as well as outcomes between e-cigarette users and non-smokers (referred to as dual users).

3. More in-depth research is needed on common chemical components in e-cigarettes and their effects on lung and heart health.

4. Clinical studies are needed to investigate the risks and potential benefits of e-cigarettes as substitutes for traditional combustible cigarettes.

5. Since the long-term health effects of e-cigarettes may take decades to manifest, more molecular and laboratory research is needed to help determine the biological effects of e-cigarette use.

“As e-cigarettes and other vaping systems have only been around in the U.S. for about 15 years, we do not have enough information about their long-term health effects, so we must rely on short-term studies, molecular experiments, and animal studies to try to assess the real risks of using e-cigarettes,” Jason Rose added. “We need to expand this type of research because the adoption of e-cigarettes is growing exponentially, especially among young people, many of whom may have never used combustible cigarettes.

The scientific statement was written by a volunteer writing group representing the American Heart Association's Council on Cardiopulmonary, Critical Care, Perioperative and Resuscitation; Epidemiology and Prevention; Cardiovascular Radiology and Intervention; Lifestyle and Cardiometabolic Health; Peripheral Vascular Disease; Stroke; and Atherosclerosis, Thrombosis and Vascular Biology. The American Heart Association's scientific statements promote awareness of cardiovascular disease and help facilitate informed healthcare decisions. Scientific statements outline the current understanding of a topic and which areas require further research. While scientific statements provide information for guideline development, they do not offer treatment recommendations.