There is a lot of material available on the Internet. Correlation between
ELO and IQ was suposed >.6 in the past, but it is only close to .2 in some
studies. Regression curves shows prediction of modest higher IQ when higher
ELO, if you pass from 1200 to 2500 ELO, the predicted difference in IQ is
in average only 10 points, but due the little correlation, it is possible
that the average difference in IQ is not the cause of the average
difference in ELO, but perhaps, at least partially, the consequence. Chess
practice has demonstrated IQ improvements in childs and young people, but
with age, the effect seems to follow a decreasing tendence, as the ELO and
IQ measures, which tend to decrease with age. After some reading I am
concluding that Chess and board games practice can be good for making you
moderately smarter, at least below the IQ measures appretiation, and it is
independent of the mastering degree you reach, but don´t expect miraculous
transformatios if you are not a boy.