I still think “increased sun exposure correlates with decreased all cause mortality” makes a better headline, but then maybe that’s why I’m not an editor.

The word 'correlates' in a title is borderline click bait-y due to possible intended confusion with 'causes'. Also it has little value. Consider the equivalent "decreased all cause mortality correlates with increased sun exposure". The word play is crazy. 'May' captures the relation and is correct philosophically.