“What makes e-cigarettes so harmful to the heart and lungs is not just nicotine,” says Florian Rader, MD, MSc, medical director of the Human Physiology Laboratory and assistant director of the Non-Invasive Laboratory at the Smidt Heart Institute. “It’s the completely unknown bucket of manufactured products used to form vapors that is likely causing the most harm.”

Rader and his colleagues compared healthy people age 18-38 who either regularly smoked cigarettes or vaped for their nicotine fix. They then measured the smokers’ and vapers’ blood flow to the heart before and after indulging—both while at rest and after performing a handgrip exercise that simulates stress.

In smokers, blood flow increased modestly after cigarette inhalation but then decreased with subsequent stress. E-cigarette users, however, showed decreased blood flow after both inhalation at rest and handgrip stress. 

“Our results suggest that e-cigarette use is associated with coronary vascular dysfunction at rest, even in the absence of physiologic stress,” says Susan Cheng, MD, MPH, MMsc, director of Public Health Research at the Smidt Heart Institute, director of Cardiovascular Population Sciences at the Barbra Streisand Women’s Heart Center and the Erika J. Glazer Chair in Women’s Cardiovascular Health and Population Science. “These findings indicate the opposite of what e-cigarette and vaping companies have claimed about their safety profile.”