You may have seen tobacco giant Philip Morris's claim that it wants to top selling cigarettes.

If so, they'll be leaving a business that leads a full 15 percent of Americans to engage in a simple, self-destructive habit that literally shaves years off their lives. 

Science suggests that 60 percent of people who try smoking go on to become daily smokers, according to a new study conducted by medical researchers in the U.K. Meantime, researchers recently found that a daily smoking habit cuts seven years from the average lifespan. 

So, just in time for the tobacco giant's skeptically-received claim (it turns out their goal is actually to replace traditional cigarette sales with e-cigaretters and vapes) here's the research, the results, and the small sliver of good news at the end.

First, the seven years...

First, a British health study that examined the biodata and lifespans of more than 600,000 people found that two sets of choices people made had the most negative impact on their lifespans: the decision to smoke, and the decisions they made that caused them to become overweight.

This wasn't just theoretical. Because they studied so many people, they were able to correlate exactly how much longer--or shorter--people lived based on their smoking habits or girth. The study was published last October in the journal, Nature.

"Our study has estimated the causal effect of lifestyle choices. We found that, on average, smoking a pack a day reduces lifespan by 7 years, whilst losing one kilogram of weight will increase your lifespan by two months," said Dr Peter Joshi, a chancellor's fellow, Usher Institute of Population Health Sciences and Informatics.

And then, the 60 percent...

Meantime, in the second study we're looking at, researchers at Queen Mary University of London studied the information that more than 215,000 people in the U.S., the U.K., and Australia had provided about their health habits in other studies. 

The data showed that somewhere between 60.9 percent and 76.9 percent of people who tried a cigarette even just once wound up becoming daily smokers, "at least temporarily." (The researchers went with the lower figure, 60 percent, due to differences in the collection of data in the pools they were working with.)

"This is the first time that the remarkable hold that cigarettes can establish after a single experience has been documented from such a large set of data," said lead researcher and professor Peter Hajek of the Wolfson Institute of Preventive Medicine. (The study was published late last year in the journal Nicotine & Tobacco Research.

(As an aside, that's a customer conversion rate that almost any marketer would kill for. Too bad the product ultimately kills the customer.)

The good news (and the not-so-good news)

None of this sounds very promising--both for people who try cigarettes, and for the overwhelming majority who wind up at least temporarily hooked.

So let's temper it with two positive developments.

The first is that the percentage of people who ever try cigarettes in the first place has fallen sharply in recent years. (Maybe that trend is why it's easier for companies like Philip Morris to say they're quitting the business.)

The second is that even if you do begin to smoke, the "seven years" study also found that people who successfully quit can get most or all of their time back.

The problem? Only about 20 percent of people who develop a smoking habit and try to quit are actually successful.

And that's considered a big improvement over the 15.7 percent of successful quitters during the past decade.

So how long does it take to make that first mistake--to smoke a cigarette just one time? Five minutes maybe? 

It turns out that the best answer you can have to that question is to be the person who's never actually it, and has to google it.

And if you ever smoked occasionally, or casually, and walked away without looking back or longing? Count yourself among the lucky ones. And enjoy your seven years.