Checking my email first thing can really be a way to throw off an otherwise productive morning. I don't see the need for science-based research here.
Personally, I've always found that my most productive days occurred when I've gotten outside and run 2-3 miles before work. All of the post-run endorphins grant me an "I can work this thing out" approach to the curveballs the day throws at me. Checking the internet, meanwhile gets me sidetracked in good conversations, such as this one, that don't necessarily move me toward my days work goals.