I can think about your question from several different angles. Ultimately, you can decide which aspects are most important to you (which may be something I mention and might not).
Medical School and Major
1. Medical school adcoms say that major doesn't matter. The biggest deals are gpa and mcat.
2. You will need to complete medical school prerequisites and prepare for the MCAT. These courses can be added on to almost any major, but may overlap with some science major requirements.
3. Most people who apply to medical school are science majors, but science majors are not necessarily preferred - sometimes adcoms want students from a variety of backgrounds and different majors.
4. Majoring in science may or may not help you with the MCAT, with medical school coursework, or in your future career. As a non-science major who scored above the 95th percentile in all science sections of the MCAT, I'm leaning toward it doesn't help with MCAT.
5. Majoring in a science, or field relevant to a medical specialty, may show early interest. Another way to show early interest in a specialty is to volunteer, work, or do research in that field.
6. You will probably need to get either 3 letters of recommendation from science professors or science professors input into a committee letter of recommendation for medical school. This may or may not be a factor in choosing a major. If you volunteer in a science professor's lab, visit them in office hours, or TA you can probably build a fine relationship regardless of your major.
7. As debatable as it is, my personal experience - as a tutor, mentor, and student - has been that science professors understand how important it is for a premed to get good grades. Sometimes professors in other majors are less sympathetic about the need for good grades.
8. Many majors are related to, or would compliment, some or all medical fields: Sports medicine, psychology, communications, education, physical fitness, marketing (transferable skills), etc.
9. IMO, it's often easier to do well in a major you like a lot. Undergrad is a special, often once in a lifetime, opportunity to study something in depth. IMO, you should pick something you truly like.
10. Money can be a limiting factor when applying for medical school. MCAT books, tutors if necessary, time off work, airplane tickets to medical school interviews, application fees can all be very expensive. Finances have kept people out of medical school before. Some people choose a major that they know is likely to get them a job and money. (Sometimes there's a gap, in time, between undergraduate school and medical school. This tends to be the case if you didn't take the MCAT during the summer of your junior year.) MCAT score and grades can boil down to whether or not you can financially afford quality tutoring, books, time off work, etc.
11. ADCOMs often want to see the full list of what you've accomplished every single year. Certain majors will make it easier to have an impressive job. (Of course, a job is just one way out of many ways, to show achievement.) Regardless of major, remember to keep track of all regular EC's, jobs, and achievements.
12. Whatever you major in, try to be distinct from most other applicants in some way. I've heard over and over again from ADCOMs and students that too much conformity is undesirable (aka the "clone" factor). If you wanted to be a very sports and psychology focused person, with a great personality, I think that could set you apart in a positive way. Perhaps you could be a peer-counselor (if your college has that), play sports, be a personal fitness trainer, or a coach as an extracurricular.
Good luck!
