Chewing gum of various kinds has been used for thousands of years.(further historical info,) In the last 100 years or so, various academic research projects have suggested that chewing gum can enhance various aspects of human cognitive behaviour. In particular, increasing attention and concentration.

The reasons behind these apparent enhancements are unknown.

A 2012 review study which looked at 26 previous research papers, concluded that "[…] gum chewing should not be considered as a learning aid or cognitive enhancer."

The present review reveals that there are clear indications that gum chewing can improve various aspects of cognitive functioning including memory, attention and both executive and intellectual functioning. However, it has to be stressed that there is also clear evidence that chewing gum during cognitive tasks can adversely affect task performance. Furthermore, a number of well-controlled studies failed to find any effects of gum chewing on cognition."

Source : Gum chewing and cognition: an overview. Neuroscience and Medicine, 3(3), 243 - 250.

Note that a number of the recent studies which found positive results for gum chewing were directly financed by chewing gum manufacturers. example