There's no doubt that smoking kills; researchers have long linked this deadly habit to heart disease, cancer and other diseases such as COPD and emphysema. That's why millions have turned to vaping as a supposedly better alternative.

According to Vapingdaily.com, about 40 million U.S. adults - or 15 percent - smoke cigarettes.

Meanwhile, the Centers of Disease Control and Prevention reports about 3.7 percent use e-cigarettes daily. That's approximately 11 million adults who are vaping, and industry experts say that the industry will grow to $5.1 billion in retail sales in the United States in 2018, according to The New York Times.

Much of the available hype on e-cigs has been linked to their so-called safety. Vaping involves puffing on vaporized liquid nicotine instead of inhaling burned tobacco. But lately, research has demonstrated that vaping comes with its own set of health risks.

Recently the University of California San Francisco conducted a large study of the health risks of both cigarette smokers and vapers and came up with startling results.

According to Business Insider, Stanton Glantz, the lead author of the study and director of the Center for Tobacco Control Research and Education, published statistics indicating that people who vape every day may face twice the risk of a heart attack compared with people who neither vape or smoke at all.

The research also says that daily conventional cigarette smokers face three times the risk of a heart attack while people who both vape and smoke—called dual users—face nearly five times the risk.

Glantz's paper, published in the American Journal of Preventive Medicine, is one of the first studies of its kind to show a significant health risk of e-cigarettes.

“We're the first people to show this long-term impact of e-cigarettes, and given that it's consistent with what we know biologically about how vaping affects the heart, we wanted to get this out there,” he told Business Insider.

Animal studies have shown that vaping could stiffen the heart and blood vessels, potentially creating an increased risk of heart disease and heart attacks.

Oddly enough, vaping has been touted to help people stop smoking, but Glantz says that the largest population of e-cig users are those who make smoking and vaping a daily habit. These are the people most at risk for heart attacks.

“E-cigarettes are widely promoted as a smoking cessation aid but for some, they actually make it harder to quit, so most people end up doing both,” he says.

Several nonprofit anti-tobacco agencies strongly oppose e-cigarettes, especially Juul, the $15 billion San Francisco startup company that manufactures the most popular e-cig in America.

Recently Israel became the first country to ban Juul devices entirely, citing health concerns linked with their high nicotine content. In a statement, Israel's' Health Ministry said the devices pose “a grave health risk.”