@Kathy in my general experience with social media you can pretty much count on the 90:9:1 rule being pretty true.
About 90% are just reading, 9% are somewhat active and then 1% are hyperactive and really running at the core of the community.
This tends to hold true online but really everywhere else too. Just think about your neighborhood or a small town and you'll find most people just live in their homes, some are more socially active, and then there are the few hyper-actives.
As far as TuDiabetes Manny can provide more insight but this is just a general rule. With 21,000 members there may be 10x that in readers and a core of 2,000 or so very active members. Would be interesting to see if Manny can verify close to that. It proves true in the communities that I run more or less, but this is a much larger community and also so emotionally passionate vs a community based around being tall or having a mohawk hairstyle.