Do a business degree, then you will study both; I would recommend majoring in finance though.
I had to do three mandatory econs for my business degree (intro microeconomics, intro macroeconomics, intermediate microeconomics), which give you a pretty good start on what economics is all about. I've completed all of my finance classes now for the degree, and I'll be doing a few econ classes next year to finish up my remaining credits.
Finance will provide you with a great deal of the background info that you need in order to approach the markets, just remember to think critically about what you are learning. There is also quite a bit of overlap between some undergrad level finance classes and economics.