I take 500mg vitamin c (plus a multi-vitamin) daily -- it helps with the inflammation in my body. My ankle feels better (I have a fractured talus, with avascular necrosis) but it also helps with my breathing. NOTHING is going to CURE my asthma -- I'm not that naive -- but, some things help make it less an issue for me . . . vitamin C is one of those things.
I've been taking C-1000's in large doses everyday for about 4 months and I used to have to use my inhaler every single day and now I never need to use it. If you take about 5000mg-10,000mg a day for a week or two it should start to help alot, then you can drop down to 3000mg a day.