Doctor Audrey Poon, working under senior author Professor Qutayba Hamid of McGill University, recently published an extensive review on vitamin D and severe asthma, including the reasons vitamin D may have a treatment effect in some patients with existing severe asthma.
I want readers to post at the end of this blog about their experiences with vitamin D and severe asthma.
Here are some of the key things on what is known about vitamin D and severe asthma.
On severe asthma in general
- Individuals with severe asthma make up between approximately 5 to 15% of the asthma population. Demographically, these patients use emergency medical care 15 times more often and are 20 times more likely to be hospitalized than patients with the milder forms of asthma.
- Patients with severe asthma are difficult to control with medication, require high dosages of medication, continue to experience persistent symptoms and asthma exacerbations in spite of aggressive therapy, and they are more likely to have irreversible airflow obstruction associated with airway remodeling.
On vitamin D-asthma observational studies
- Observational studies have demonstrated an involvement of vitamin D deficiency in severe asthma. Taken together, data from observational studies are suggesting a protective role of vitamin D in severe asthma.
- In a study of moderate and severe asthmatic individuals who were vitamin D insufficient (defined as less than 30 ng/ml), those who exhibited steroid resistance had a significantly lower frequency of T regulatory cells (Treg cells help the body distinguish self from non-self and prevent the body from attacking itself). Furthermore, in these individuals serum 25(OH)D level was strongly associated with Treg cell number.
- In a childhood cohort of mild to moderate persistent asthma who received inhaled corticosteroid, lung function improvement was the greatest in the vitamin D sufficient group (defined as greater than 30 ng/ml) as compared to the vitamin D-deficient group (defined as less than or equal to 20 ng/ml).
On mechanisms of vitamin D in asthma
- Vitamin D regulates transcription of several genes that are involved in airway remodeling in airway smooth muscle cells.
- The anti-inflammatory effect of vitamin D in airway smooth muscle cells has been demonstrated by the observation that treatment of vitamin D suppressed the secretion of inflammatory cytokines (IL-5, IL-6, IL-8 and tumor necrosis factor-α).
- Vitamin D should exert its anti-proliferative and anti-inflammatory effects in existing asthma by modulating cell cycle, transcription, and translation of genes involved in inflammation and airway remodeling.
- Vitamin D may synergistically promote the anti-inflammatory action of glucocorticoids by recruiting eosinophils away from the site of inflammation via up-regulation of a gene (CXCR4).
- Evidence exists suggesting that vitamin D would decrease scarring (fibrosis) and promote remodeling in the airways of asthmatic individuals.
On clinical trials
- In an ongoing study, children with severe asthma taking vitamin D in addition to steroid therapy had a lower percentage of asthma attacks compared to the steroid only group.
- In the next two years, several large clinical trials of vitamin D supplementation to prevent asthma and related morbidity will be complete, according to the United States Clinical Trial registry.
- In severe asthma, three trials are in the planning stage to see if vitamin D supplementation would reduce asthma exacerbation rates in moderate to severe asthmatic adults. That is, they will see if vitamin D is effective treatment for existing asthma.
What all this seems to imply is that not only may vitamin D help prevent asthma, but it may have a treatment effect in existing severe asthma. If you have severe asthma and decide to try vitamin D, make sure you use it as add-on therapy. That is, take vitamin D in addition to your regular asthma meds, not in place of your asthma meds.
If you have asthma, or have had asthma, especially severe asthma, please blog about your experience with vitamin D and asthma.
Lastly, check out our patient friendly summary on vitamin D and asthma and be sure to share with your friends.