In an article written in the medical journal "Thorax" by Dr. N.J. Wareham et al of Medical Research Council in Cambridge, UK reveals that modification of diet can reduce onset of asthma.  It is reported that people who suffer with asthma tend to consume less fruits and have decreased intake of Vitamin C and manganese.  It was also reported that blood levels of vitamin C were lower in people with asthma than their healthy counterparts. 

 So eat your raw meal each day, take your enzymes for good absorption of vitamins and minerals  and eat more vitamin C foods.  I have seen vitamin C to be extremely good for asthma.  I have actually seen it stop wheezing associated with an episode of asthma almost immediately.