To say or to keep my mouth shut

So I have this friend. She has been my friend since I was 9 years old. I have to say that I cherish our friendship, although we both have our own lives and families and only get together a few times a year. We talk about once a month or so - always with promises to get together soon, but i have to say that the times are getting further and further apart. Let me just say that my friend has always struggled with her weight, and I believe because of that her self esteem. You wouldn't really know that she struggles with her self esteem though because it's not something she ever talks about. My friend has always been a bit heavier and when she was growing up her stepdad would continually make comments of the rude variety about her size, her eating habits or whatever- it didn't help. Friend met her first boyfriend in grade nine. He was a few years older. They liked to party, hang out and eat. Years later, when they married, they were both the heaviest I had ever seen them. I suppose looking around at people nowadays, this is a pretty common thing. But in my small confined community of family and friends it is not. A few years after they had their first child, both husband and wife decided to get healthy. I started going to the gym on a tri-weekly basis with my friend and we were having a lot of fun. We were in our late twenties and we had lots of time to do what we needed to get in the best of shape. Friend was overjoyed when she no longer had to shop at plus sized stores. things were good in the world. Shortly after I got married, started having kids of my own, moved out of the neighbourhood and thus don't see my friend on a daily basis anymore. My friend switched careers within the same healthcare field and is now working in a weight control help centre. Oddly enough the new place of work has had an opposite effect on her as both her and her husband have been putting on weight again. Last year my friend called me completely distressed. (Have I mentioned friend very rarely lets any of her true feelings out? She is a bottle waiting to burst!) She had her husband at the doctors office. The dr. told her that they needed to get husband to the hospital right away. Apparently they discovered during a routine procedure, that his blood pressure was through the roof. I mean practically at stroke level. I couldn't believe the news. So, what was the diagnosis? What was the course of action? Lifestyle change of course. No more booze, no more red meat. plenty of excersize etc. and of course, pharmaceuticals. So husband took the pharmaceuticals (of course) and for a month or so laid off the booze and bad food. That was it. I never heard about it again. Every conversation was about the last restaurant they ate at or the drinks they had etc etc. Never again did I hear a peep about the illness or blood pressure or the lifestyle adjustments they were supposed to make. Now I spoke with friend the other day. She mentions a dr.'s appointment that she has gone to for sleep apnea. I am troubled by this. I ask her, and she says she has been having trouble sleeping and she has gone to a sleep disorder clinic and they tell her that she has sleep apnea, but not to worry because it doesn't have anything to do with weight. (At this point I don't know what to say because it is fairly common knowledge that sleep apnea is associated with weight and it can be cured with weight loss- something I am sure that she knows, but is somehow either avoiding or denying) Of course it is now 2 months later and I have not heard anything about this ailment again. It's as if it has totally disappeared. Plus she has been having issues over the past couple of years with swollen ankles and now her knees are starting to bother her as well.
The real purpose of this post is to A) be cathartic and B) figure out whether or not I should mention something or just let it lie.
In the past I have always let things lie. My thought behind this was that if she wanted to discuss things, she would bring them up and I would provide an ear to listen. I know that she knows I will always be an ear for her and that I wouldn't judge her. I know this because shortly after my first child was born there was an issue where she either thought her husband cheating or he actually was cheating. We don't know for sure, but there was a rough spot in her marriage there and she called and we spoke for a time. of course, true to nature, this too was soon passed over and never spoken of again shortly after a few poignant conversations.
I don't know if I need to add that this is not my personal method of dealing with things. I am the "up front" and transparent type of person. I like to confront, discuss and deal with things either before or as they occur, so I am at a loss even in terms of understanding the passivity of her nature.
What is one to do?
Am I a good friend to stay in silence?
Just my thoughts on this issue. I don't want to be apathetic, but I don't want to intrude where I don't belong either.