I've never built an mhealth startup, but I have spent a lot of time researching and implementing gamified product experiences. I would suggest the following resources:

1) Anything Gabe writes + videos online
http://www.gamification.co/gabe-zichermann/

2) Anything Nir writes + watch his videos online
http://www.nirandfar.com/
On Clarity: https://clarity.fm/nireyal

3) Anything Amy Jo Kim writes + talks
http://amyjokim.com/
On Clarity: https://clarity.fm/amyjokim

These are the 3 people I turn to .. they're brilliant

Not directly related to your question, but I would be careful about passing user health data to the Game Center. I don't have enough details about your product, but here in the States there are strict privacy requirements dictated by HIPAA when it comes to protected health information (PHI). You may not want to tie a user account (in game center) to health activity depending on exactly how it's going to be used and whether it would fall under PHI as defined by HIPAA.

Also, as a diabetic myself, the idea sounds pretty cool. If someone could gamify my regular blood sugar testing I'm sure I'd be more compliant with my testing schedule :)

Hi. I remember working on a project with a large pharma company around gamification for diabetics, and the core issue sounds similar.

The real question is what can I do with the points? In Crush they were mainly used for more lives to keep that addiction going. Sometimes for bonuses to get through a level. Are you doing the same purchase for the points, or is it mainly a leader board scale. Yours could be used to create and upgrade an avatar / virtual pet, which can be used to increase the self image of your players.

If those points are then also given later by a much more strenuous activity, i.e. x pounds, it may throw the game balance off. Multipliers could be used for the weight loss, to rebalance that grinding. Think about the behavioral feedback loop you want to reinforce with the player, and add the gratification at those peak moments of the cue, routine and reward.

Feel free to call if you would like to discuss the problem in more depth.