Breathing training may improve your quality of life and decrease the amount of medication you need, but isn't likely to control your asthma alone.
Researchers from the Department of General Practice and Primary Care at the University of Aberdeen in Aberdeen, UK performed a randomized controlled trial--a type of research trial designed to see if one method is more effective than another method--to determine if formal breathing training improves quality of life and actual asthma control. Respiratory therapists provided breathing training for one group of patients, while nurses provided standard asthma education to the other group. The intervention consisted of specific abdominal (belly) and nasal breathing techniques. Participants were encouraged to practice the exercises for at least 10 minutes each day.
After six months, quality of life scores were significantly improved in the group performing breathing training exercises compared to the group receiving traditional asthma education. Additionally, measures of anxiety and depression were also decreased among the respiratory training group. However, while the breathing training was associated with slightly better reported control of asthma symptoms, measures of actual, objective asthma control like peak expiratory flow rate were not significantly different between the groups.
While this study did not demonstrate a decreased need for asthma medication, other studies have shown a decrease in both rescue inhaler use and inhaled steroids. Breathing training may benefit patients whose asthma impairs their quality of life. Importantly, the intervention was relatively brief and differences persisted for six months without additional training
So what is the take home message for me and my asthma? Breathing training may not decrease your need for medication, but it may significantly improve your ability to live with your asthma and decrease anxiety or depression related to asthma. Importantly, breathing exercises are not hard to learn, won't cost you anything, and can be learned in a short time period.
For more information, check out a series of videos that demonstrate how to do breathing exercise that were shown in a 2006 article to improve not only quality of life, but also asthma control.
Mike Thomas et. al. Thorax (2008). Breathing exercises for asthma: a randomised controlled trial. Published Online First: 3 December 2008.

Oh, interesting! I have bookmarked the page with the videos.