Bronchiectasis is a disease caused by localized, irreversible increase in the diameter of part of the bronchial tree caused by previous destruction of the muscle and elastic tissue. It is classified as an obstructive lung disease, along with emphysema and chronic bronchitis. Involved bronchi are dilated, inflamed, and easily collapsible, resulting in airflow obstruction and impaired clearance of secretions.
Bronchiectasis may result from previous infections, immunodeficiency or infection with aspergilla. A causative factor is found in about half of cases, but in only 15% is a firm cause amenable to specific treatment discovered. The high percentage of patients with unknown etiologies reflects our poor understanding of the disorder. Both mortality and hospitalization rates studies indicate that the incidence of bronchiectasis is increasing.
Many adult patients describe chronic productive cough and unresolved infection during childhood, symptomatic improvement in late adolescence, and then deterioration from the age of 50 years. The disease is characterized by productive cough and repeated respiratory infections, the frequency of which varies widely, but which usually requires antibiotics. More severe exacerbations often require hospital admission and prolonged courses of antibiotics. Bronchiectasis increases mortality and has an enormous impact on quality of life.
Until recently, healthy lungs were considered sterile. However, it appears the lungs are inhabited by a diverse range of bacteria (microbiotia), present in low concentrations. Significant differences in the lung microbiotia between healthy and COPD patients have been described. The microbiotia of the healthy lung often bacterial sequences similar to normal upper respiratory flora but a more pathological association is the case in bronchiectasis. For example, in a recent study, 75% of patients with bronchiectasis also had chronic sinusitis.
Dr Jim Bartley and colleagues of the University of Auckland recently summarized the reasons vitamin D may be helpful in preventing and treating bronchiectasis.
They made the following points:
- The innate immune system provides an immediate defense against infection. Innate immunity includes both extra and intracellular components and vitamin D influences innate immune function through both systems.
- Vitamin D upregulates antimicrobial peptides (AMP), which are molecules synthesized and released by the lining of the lungs and white blood cells. AMP target the lipoprotein microbial cellular membrane, a membrane that distinguishes microbial cells from human cells.
- Nitric oxide (NO) is produced as bursts lethal to microbes within white blood cells after those white cells engulf the microbe. Activated vitamin D induces intracellular NO synthesis by white blood cells.
- Certain cells of the immune system called dendritic cells process microbial material and present that material to other cells of the immune system, including killer T cells. Vitamin D appears to modulate dendritic cell presentation.
- Activated vitamin D stimulates the development of T regulatory lymphocytes (cells that help distinguish good self from foreign non-self) via a direct effect on lymphocytes resulting in them developing into T regulatory cells.
- Immunoglobulin G levels, which are a marker of lung disease severity in bronchiectasis patients, are inversely correlated with 25(OH)D levels.
- Patients with bronchiectasis who were vitamin D deficient were more frequently chronically colonized with bacteria, had a lower lung function tests, had more frequent pulmonary exacerbations, and had higher inflammatory markers.
The authors concluded,
“Bronchiectasis is a chronic, debilitating disease that causes significant morbidity and mortality. Basic science indicates that vitamin D could reduce the frequency of respiratory infective exacerbations, as well as airway inflammation. Low 25(OH)D levels are seen in adult patients with bronchiectasis. Theoretically, vitamin D3 supplementation could be useful in patients with bronchiectasis.”