Bear in mind that the "dirty little secret" in med school is that the grades in the clinical years, especially the first year, barely count --they have very little bearing on your future. It's foundation, and some of that stuff is fair game for step 1, but how you do isn't going to make or break you career-wise as much as the rotations later in med school.
So if you majored in it in college and then re-covered it in med school you just got foundation for the foundation. You won't get much of a leg up but even if you did, so what -- the guy who learned it in med school and did better on Step 1 is still going to get better interviews, even if you aced that first year course.
So this is why you should major in what you enjoy, even if it has little to do with what you'll be doing in med school. Especially if it has little to do with what you'll be doing in med school. In fact, it might pay to take courses in college you won't be retaking in more detail later so you get the benefit of learning more things. Major in business with a minor in spanish and you'll be far better off as a physician, career-wise.