I'm reading less of JAMA these days. They recently changed the font they use in some sections of the journal, and it's not easy on my eyes.
There are two basic types of font: serif and sans serif. "Serif" is Latin for "tail," and "sans" is Latin for "without."
Sans serif ("without tails") fonts include Arial, Helvetica, and Verdana.
Note: no little tails hanging off the edges of these letters.
Serif (with "tails") fonts include Times New Roman, Georgia, and Courier.
Note: the little dashes or squiggles on the tops of the w, along with the extra lines on the N and the T.
(Here's Arial's w, N, and T for comparison.)
Sans serif fonts are easier to read far away; your brain doesn't have to work as hard to make out the letters without those tails. When I teach presentation skills workshops, one of the points I focus on is that projected material should always be in sans serif font. (Try observing what happens to your interest and fatigue level during the next PowerPoint presentation you see with serif font.)
Interestingly, computer screens seem to be just far enough away that most people prefer a sans serif font. Look at the fonts on your favorite web sites, and, chances are, they will be sans serif.
Those tails, though, theoretically make reading close-up easier and less fatiguing on the eyes. (Try observing what happens to your interest and fatigue level while reading the next printed material you come across in a sans serif font.) I must admit that most of the studies done regarding readability disagree with me regarding serif fonts for reading, but my personal experience has shown a definite preference for serif fonts on printed materials. JAMA is the only journal of the Top 10 impact factor medical journals, by my cursory review, to use sans serif font for some of its articles, so perhaps others share my bias toward serif fonts for close-up readability.
Not only did JAMA change several of its printed sections to a sans serif font last year, but they also dramatically reduced their font size throughout the whole journal. I know that journals are trying to cut costs and stay relevant in an increasingly online world, but I am much less likely to read print material with eye-taxing font styles and sizes. I actually prefer reading paper to the glare of a computer or tablet LCD screen, and I hope that print journals will find a way to continue delivering at least some content in a reader-friendly manner.
Take some time to observe fonts, both on big screens and close-up. Which seem most comfortable to you?