Researchers suggest delivering vitamin D directly to the lungs could bypass the limitations of oral supplements in treating COPD and asthma.
RT’s Three Key Takeaways:
- Oral Supplement Inefficacy: Randomized controlled trials have consistently failed to show that oral vitamin D supplements improve lung function or reduce exacerbations in patients with chronic respiratory conditions.
- Enzymatic Barrier: Researchers suggest that oral vitamin D is inactivated by an enzyme in the lung’s blood vessels before it can reach the airway tissue where it is needed.
- Targeted Delivery Potential: Delivering vitamin D directly to the lungs via inhalation could bypass vascular inactivation, potentially offering a low-cost treatment to reduce inflammation and the frequency of flare-ups.
Researchers at the University of North Carolina (UNC) School of Medicine are proposing inhaled vitamin D as a new strategy for treating chronic lung diseases, according to a perspective published in Chronic Obstructive Pulmonary Diseases: Journal of the COPD Foundation.
Patients with COPD, asthma, and cystic fibrosis frequently have low vitamin D levels, which are linked to poor respiratory outcomes. While observational studies show a strong association between vitamin D deficiency and increased hospitalizations or reduced lung function, oral supplements have failed to demonstrate clinical benefits in randomized controlled trials.
“We think the reason is that oral vitamin D gets inactivated by an enzyme in the lung’s blood vessels before it ever reaches airway tissue,” said Kevin Schichlein, PhD, first author and postdoc in the Marsico Lung Institute, in a news release. “Delivering it directly to the lung through inhalation could bypass that problem entirely.”
Addressing the Delivery Disconnect
When vitamin D is taken orally, it is processed by the liver and enters the bloodstream. Researchers suggest that as the vitamin travels to the lungs, an enzyme in the blood vessel cells inactivates it before it reaches the air spaces. This prevents the compound from reaching the lungs in a high enough concentration to provide a therapeutic effect.
Direct delivery to the airways could allow the vitamin to reach its target while reducing the amount of the compound circulating through the rest of the body.
“Topical or inhaled delivery of vitamin D is already being explored for upper airway diseases with data from preclinical models and some preliminary clinical trials showing promising results,” said Ilona Jaspers, PhD, co-author and professor in pediatrics. “Moving to the lower airways could be a logical extension of these observations.”
Future Therapeutic Opportunities
The researchers emphasized that while observational data consistently link deficiency to adverse outcomes, the method of delivery is likely the reason clinical trials have failed to show improvements in quality of life or exacerbation rates.
“There has been a longstanding disconnect between the established harms of vitamin D deficiency and the failure of clinical trials of oral vitamin D supplementation to improve respiratory healthcare,” said M Bradley Drummond, MD, co-author and professor of medicine. “We believe this disconnect may reflect a suboptimal delivery method for vitamin D rather than its overall ineffectiveness.”
If clinical trials confirm that inhaled vitamin D is safe and effective in humans, it could serve as an affordable supplement to existing treatments. Because the compound is already well-characterized, the primary shift involves treating the lung as a local target.
“If inhaled vitamin D proves safe and effective in clinical trials, it could be a low-cost add-on to existing treatments for the millions of people living with chronic lung disease,” said Schichlein. “The compound itself is already well-characterized and inexpensive. The novelty comes from treating the lung as a local target rather than assuming a pill will eventually reach the lung.”
