I had to temporarily give up any serious violin playing for my medical/surgical training. For that matter, I've given up tons of sleep too. I trained (residency) in the era before they limited the time in the US to 88 hours of work per week (80 hours plus a allowable 10%).
I don't know if playing an instrument has anything do with being smart. There are probably theories of playing while you're very young and it develops certain parts of the mind (ie - music playing ability).
For me, I know that my music has hurt my grades many many times. When I was in high school, my parents would try to make me stop practicing (violin) so that I would focus more on school work. And I still remember the comment said to me: " if you only worked as hard on your school work as you do on the violin, you might actually get good grades." Heck, I graduated Validictorian anyway (got lucky?). Many of the top students in medical school didn't play any instruments at all. They have always been super focused on grades and studying and had no time for music, I guess. The exception is another surgeon I know who graduated #1 from her medical school, that wanted to play piano as a child but her parents wouldn't let her have lessons, so she taught herself how to play (because there was a piano lying around in her house). She stopped playing piano in highschool/college/medschool/residency/fellowship because she didn't have time and didn't have access to a piano. Well, let's just say she made up for lost time by getting the Steinway B that sits in my house. However, she and I have to fight over time on that piano.