Some Greek scientists have recently called for further studies on the safety of electronic cigarettes, saying scientific knowledge about the object was "very limited".
Electronic cigarette, or the so-called e-cigarette, first manufactured in China and sold mostly through the internet.
The cigarette is a battery-powered equipment that emit a blast or a harmless smoke nicotine into the lungs and is intended to replace normal cigarettes and help smokers break their habit.
These products became the center of legal upheaval in the United States between the maker and the U.S. Food and Drug Agency (FDA), which regulates drugs and want to stop the electronic cigarettes are imported into the U.S..
But the interpretation of the three reports was mixed. New Zealand study of electronic cigarettes should be advised states because it is safer than smoking tobacco, and the study of Greek speaks of a more neutral stance.
"The limited information given in these three reports represents all the knowledge we currently have about e-cigarette," wrote Andreas Flouris and Dimitris Oikonomou, from the Institute of Human Performance and Rehabilitation in Greece, in the British Medical Journal.
"This may be one reason why the struggle ... between the FDA and the makers of electronic cigarettes have been so heated," he said.
A U.S. judge last week issued a ruling prohibiting the administration of U.S. President Barack Obama is trying to ban imports of electronic cigarettes, saying the move was part of "aggressive efforts" by the FDA to regulate "tobacco products for pleasure".
Tobacco is the leading cause of preventable death in the world, killing more than 5 million people per year. A report by the World Lung Foundation last August said smoking could kill one billion people this century if trends hold.
Flouris and Oikonomou said that while "smoking strategy choices are always welcome in an effort to reduce the threat to public health" caused by tobacco, security is also important ".
"Chemical analysis required a more active, followed by extensive research that involves the study of animals and, ultimately, clinical trials in humans,"