Following a 50-year concerted effort by U.S. regulators to help Americans drop their tobacco habit, the proof is in the pudding of their success based on a Morbidity and Mortality Weekly Report released late last year.

Source: Centers for Disease Control and Prevention.

In its report the Centers for Disease Control and Prevention noted that there are now just 42.1 million people aged 18 and up that are lighting up compared to 45.1 million in 2005. This marks an all-time record low in terms of the percentage of adults (17.8%) that smoke. Furthermore, the number of heavy smokers is on the decline. Just 7.1% now smoke 30 or more cigarettes per day compared to 12.7% in 2005. Smokers in the 20-29 cigarette per day category also saw a decline.

Innovative products do their part
This drop in tobacco users is great news, as smoking has been linked to an increased risk for heart disease and lung cancer. Part of this drop can be attributed to improved education of the American public that's highlighted the dangers of smoking, especially with America's youth. The other component is improved access to smoking cessation agents.

One of the most popular products that Americans are using to help kick the habit is electronic cigarettes. An electronic cigarette heats a flavored liquid containing nicotine into a vapor which is then inhaled by the user. The presumption is that simply inhaling the nicotine vapor and liquid is much healthier than inhaling tobacco smoke, which is known to contain a number of carcinogens.

Source: Flickr user Jon Williams.

Per a CDC study in September, 8% of adults had at one time used an electronic cigarette. The rapid rise of electronic cigarettes allowed Lorillard (NYSE:LO.DL) to garner about half of all U.S. e-cigarette market with its Blu brand, which is actually being divested due to Lorillard's purchase by Reynolds American (NYSE:RAI). Electronic cigarettes are viewed by tobacco companies as a solid hedge against a five-decade decline in adult smoking rates.

But, it turns out the benefits of electronic cigarettes may actually be outweighed by their risks.

Electronic cigarettes: Not as great as first advertised?
According to a study released just three weeks ago by National Jewish Health, a nonprofit hospital organization focused on improving patients' respiratory health, the liquid used in electronic cigarettes has been linked to a considerably higher risk of respiratory viral infections. What's more, it didn't matter whether or not nicotine was present in the liquid solution. The findings showed it was the liquid vapor itself that can damage epithelial cells in users' airways and lead to an increased risk of viral infections.

Source: Flickr user Manymeez.

The study utilized human epithelial cells at one end of a sterile container and an electronic cigarette at the other. Scientists noted that within minutes of being exposed to the electronic cigarette vapor, an immune response was witnessed in the epithelial cell samples as measured by an increase in IL-6 protein levels. Further, this increase in IL-6 protein levels lasted for up to 48 hours. The implication is that vaping liquid damages the cells in our airways almost immediately by causing inflammation, and its effects aren't gone for up to two days later.

Worries are mounting
The truly scary thing for electronic cigarette users and manufacturers is that this latest study from National Jewish Health is just one of many growing concerns about electronic cigarette usage.

For starters, there's pressure building regarding the way that electronic cigarette manufacturers and liquid vapor producers are marketing their product. With more than 400 flavor combinations, some of which seem geared toward a younger generation (e.g., bubble gum, mango, and caramel apple), consumers have to wonder whether these companies are truly trying to get users off cigarettes, or if they're trying to hook a new generation of young adults on nicotine. To be fair, an argument could be made for both sides here with many newer companies trying to completely disassociate themselves from cigarettes by utilizing crazy flavors. However, it's clear that e-cig producers' marketing tactics are under fire.

Source: Flickr user Lindsay Fox.

The bigger concern here might be the eventual involvement of the Food and Drug Administration. Everything will depend on whether or not the FDA decides to classify electronic cigarettes and their liquids as tobacco products or not. If they are eventually reclassified as tobacco products they'll be fully regulated, right down to each new vaping flavor that's introduced.

Why might the FDA regulate the electronic cigarette industry? Actually, there are a few reasons. First, we don't really know a lot about the long-term health effects of e-cigs (and National Jewish Health's study isn't helping their cause). Secondly, and adding to the point above, there's concern that minors' access to electronic cigarettes could be too easy if they aren't regulated. Finally, it's a simple matter of quality control. No one really has any clue if new vaping liquid flavors are of the same quality as prior vaping liquid. Having the FDA step in would ensure that the quality of liquid remains consistent. In addition, we'd also have a better idea of what's in the liquid.

Here's what I'm doing
Considering the growing evidence that's working against the long-term safety and proliferation of electronic cigarettes, my inclination for the time being, as an investor, is to stick to the sidelines.

Even though e-cig usage appears to have ballooned from five years ago, it's really plateaued over the past year on the heels of new safety studies and questionable marketing tactics. I find it very plausible that the FDA is going to step in and regulate the electronic cigarette industry sooner than later, if not for the purpose of regulating the production of the vaping liquid, then for the sake of ensuring that minors don't have access to the product.

We obviously still have a lot of data to pour through over the long-term, which could dramatically change the way we currently view electronic cigarettes. However, the way things stand now, the risks of investing in this sector appear to greatly outweigh its potential rewards.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.