As the use of e-cigarettes continues to rise, concerns about their long-term effects on health have persisted. Now, a new study finds that smokers who switch to e-cigarettes only - much like those who switch to nicotine replacement therapy only - have fewer carcinogens and toxins in their bodies after 6 months, than those who continue to smoke combustible cigarettes.

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The study adds to growing evidence that e-cigarettes are a much safer alternative to smoking conventional tobacco cigarettes.

The Cancer Research UK-funded study is published in the Annals of Internal Medicine.

According to the World Health Organization, tobacco use kills around 5 million people who smoke per year, and more than 600,000 non-smokers who are exposed to second-hand smoke.

At least 250 of the 4,000 chemicals in tobacco smoke are known to be harmful, including 50 that are known to cause cancer (carcinogens).

Electronic cigarettes (e-cigarettes) are battery-operated devices that deliver nicotine that is flavored, as well as other chemicals through vapor instead of smoke.

In the United States, there are more than 250 brands of e-cigarette on the market. Some look like traditional combustible cigarettes, cigars, or pipes that deliver nicotine by burning tobacco, while others look like everyday items such as USB memory sticks and pens. The newer, refillable devices may look different.

Study analyzes intake of chemicals

While e-cigarettes are often promoted as safer alternatives to traditional, combustible cigarettes, the authors of the new study note that there has not been much research on the long-term health effects of e-cigarettes.

Some reports suggest that e-cigarettes cause as much harm as combustible cigarettes, but the study authors note that they are based on research that does not reflect real-world exposure of e-cigarette users.

The new study is the first of its kind because it analyzes intake of potentially harmful chemicals.

Previous studies have measured potential toxicity of e-cigarettes by analyzing chemicals in the products and the vapor they produce.

E-cigarettes may be a useful long-term quitting aid

From saliva and urine samples, the researchers measured the intake of potentially harmful chemicals in various groups of people, including: former smokers who used e-cigarettes only for 6 months; former smokers who used licensed nicotine replacement therapy (NRT) only for 6 months; and smokers who continued to smoke combustible cigarettes.

Fast facts about giving up smoking
  • Research shows that few people are aware of the specific health risks of tobacco use
  • Most smokers who are aware of the dangers want to quit
  • Counseling and medication can more than double the chance of successful quitting.

Learn about giving up smoking

The results showed that while their levels of nicotine remained much the same, former smokers who had used e-cigarettes only or NRT only for 6 months had significantly lower levels of toxic chemicals and carcinogens in their bodies than the people who continued to smoke combustible cigarettes.

However, participants who used e-cigarettes or NRT while continuing to smoke combustible cigarettes did not show the same large reduction, suggesting that there must be a "complete switch" to see a significant reduction in exposure to toxins.

Lead author Dr. Lion Shahab, a lecturer in the department of epidemiology and public health at University College London in the United Kingdom, says that their study confirms that e-cigarettes (like NRT) are far safer than smoking, and adds that:

"We've shown that the levels of toxic chemicals in the body from e-cigarettes are considerably lower than suggested in previous studies using simulated experiments. This means some doubts about the safety of e-cigarettes may be wrong."

He and his colleagues suggest that e-cigarettes may be a useful long-term aid to smoking cessation for people who struggle to quit using other methods. However, they warn that the health benefits will only accrue if users stop smoking combustible cigarettes completely.

"This study adds to growing evidence that e-cigarettes are a much safer alternative to tobacco, and suggests the long-term effects of these products will be minimal."

Alison Cox, director of cancer prevention, Cancer Research UK

Learn how smoking 20 cigarettes per day for a year could mean 150 lung cell mutations.