Dietary supplements, such as the vitamin B supplement show above, are typically sold in pill form. (Photo credit: Wikipedia)
The BBC News reports that taking vitamin D supplements in addition to asthma medication appears to reduce the risk of severe asthma attacks, citing a review of the evidence.
Source: Vitamin D ‘significantly reduces severe asthma attacks’ – BBC News
With no downside risk from taking vitamin D supplements, it would appear beneficial for asthma suffers, especially those that do not get regular exposure to the sun. However, the benefits are marginal and no substitute for regular medication.