People who quit smoking and then took up vaping were more likely to develop lung cancer than those who did not vape, according to the study conducted in South Korea.
"This is the first large population-based study to demonstrate the increased risk of lung cancer in e-cigarette users after smoking cessation," said Yeon Wook Kim, who led the study at Seoul National University Bundang Hospital.
Ex-smokers who vape at higher risk of lung cancer
The researchers examined 4,329,288 individuals in South Korea, who had a history of conventional smoking. They took readings at two time points: 2012-2014, 2018, and in a follow-up in December 2021.
By the time of the follow-up reading, the researchers found that 53,354 individuals had developed lung cancer and 6,351 had died from lung cancer in the intervening period.
Former cigarette smokers who took up e-cigarettes were at a greater risk of a lung cancer diagnosis and cancer-related death than ex-smokers who had quit and avoided e-cigarettes as well.
"Our results indicate that when integrating smoking cessation interventions to reduce lung cancer risk, the potential harms of using e-cigarettes as an alternative to smoking must be considered," Kim said.
Are vapes less harmful than tobacco cigarettes?
E-cigarettes heat a liquid that becomes a vapor you inhale. They sometimes contain tobacco, which is the main harmful part of cigarettes that causes cancer.
However, e-cigarettes contain other potentially harmful chemicals, albeit at lower levels than tobacco cigarettes.
"Dangerous chemicals found in vaping products that can damage lungs include acrolein, formaldehyde, diacetyl, and ultrafine particles that can be deeply inhaled. Vaping products can also include heavy metals such as lead," said Ashley Merianos, an associate professor at the University of Cincinnati in the US.
Many health care professionals and organizations believe e-cigarettes are substantially safer than smoking tobacco. Vaping is also recommended as a tool to help quit smoking cigarettes.
Experts have said e-cigarettes are safe in the short to medium term, but it's unlikely they are risk-free in the long term.
Merianos said there were many unknowns about vaping, especially those concerning long-term human health effects.
"Budding evidence suggests that vaping may be linked to lung problems, including asthma. Additionally, the limited studies we have indicate that secondhand aerosol exposure is associated with respiratory symptoms and illnesses," Merianos told DW, adding that it was possible secondhand exposure to aerosols from vaping products could also be harmful.
Do e-cigarettes cause cancer?
E-cigarette liquids can contain very low concentrations of numerous chemicals that are known to cause cancer. A heavy user may inhale these chemicals multiple times a day, every day, for many years.
But is there evidence that vaping directly causes cancer? No, not really — it's currently unknown what extent of exposure is sufficient to cause cancer.
On the one hand, studies show that vaping short-term, for less than two years, is not associated with a rise in cancer diagnoses.
But this latest study from South Korea is one of several more recent studies indicating that vapes may increase the risk of developing cancer later in life, at least for people who used to smoke conventional cigarettes.
A study published in March 2024 found that vape users and cigarette smokers had similar changes to DNA of cells in their mouth.
Such changes have elsewhere been linked to future development of lung cancers in smokers, but do not prove that people who vape will necessarily develop cancer.
Merianos said researchers lack the overall evidence to make conclusions about the long-term health effects of vaping, including cancer outcomes.
The science is also inconclusive about whether vaping is harmful to some people more than others, for example in pregnant women or in children.
