A 2009 study of Norwegians found that heavy smokers—those who puff at least 20 cigarettes per day—were 2.5 times more likely to die over a 30-year period than nonsmokers. But the cardiovascular risks associated with smoking aren't just seen in chain smokers.
The more nuanced message that doesn't always get across is the risk that the occasional smoker is exposed to. Even 10 minutes of secondhand smoke exposure may affect cardiovascular function. Just because you might not smoke a pack a day or even a week doesn't mean you're in the clear. "There is no safe level of exposure" to tobacco smoke, says Yancy.
Bottom line To protect against heart disease (not to mention cancer, stroke, and reproductive problems), the goal is to smoke exactly zero cigarettes.
(credits to YahooNews)