Some flavorings in electronic cigarettes (“e-cigarettes”), even without nicotine, can increase the risk of heart disease. Dr. Joseph Wu, director of Stanford University’s cardiovascular institute, and his team published a study in the Journal of the American College of Cardiology that found human cells exposed to e-cigarette flavors indicated blood vessel dysfunction. Overall, the type of cells studied that line healthy blood vessels showed signs of damage and were less able to form new blood vessels or heal wounds after being exposed. Another study looked at health records to conclude e-cigarette users had a higher risk of heart attack than people who neither vape nor use tobacco products. Dr. Wu warned that people who already have heart disease may think switching from tobacco to e-cigarettes is enough protection, but they are not completely safe from harm.