Washington: Are you trying e-cigarettes or other nicotine replacement therapies to overcome addiction to cigarette smoking? Be warned, as they are not as safe as you might have assumed, said a study.

Small dosages of nicotine found in cigarette substitutes could be harmful to human musculoskeletal system, due to overuse, the study said.

"E-cigarettes are marketed as safe alternatives to cigarette smoking, however, the harms associated with their overuse have not yet been widely investigated," said senior study author Herman Cheung, a professor at University of Miami in the US.

Interestingly, the findings show that nicotine can be beneficial at low dosages. For example, exposure to low dosages of nicotine promotes collagen production and skin wound repair.

Yet at higher dosages, cells involved in the wound and skeletal healing processes actually become ineffective.

That is why overuse of nicotine-replacement therapies, which still contain small amounts of nicotine, can present a health risk, the researchers said.

"It has been widely documented that smokers, compared to non-smokers, experience prolonged delays in bone healing, after a bone fracture," Cheung said.

"We believe that nicotine significantly affects the potential for stem cell proliferation, migration and osteogenic differentiation - the potential of a cell to become a bone cell," he said.

"We think that these effects cause delays to bone healing," Cheung noted.

For the study, the researchers investigated and summarised the last five years of studies, on the effect of nicotine on wound and skeletal healing processes in humans.

The findings appeared in the Global Journal of Medical Research.